Quantum to classical crossover of Floquet engineering in correlated quantum systems - Sentef, Michael A.; Li, Jiajun; Künzel, Fabian; Eckstein, Martin (Physical Review Research, 2020)
Light-matter coupling involving classical and quantum light offers a wide range of possibilities to tune the electronic properties of correlated quantum materials. Two paradigmatic results are the dynamical localization of electrons and the ultrafast control of spin dynamics, which have been discussed within classical Floquet engineering and in the deep quantum regime where vacuum fluctuations modify the properties of materials. Here we discuss how these two extreme limits are interpolated by a cavity which is driven to the excited states. In particular, this is achieved by formulating a Schrieffer-Wolff transformation for the cavity-coupled system, which is mathematically analogous to its Floquet counterpart. Some of the extraordinary results of Floquet engineering, such as the sign reversal of the exchange interaction or electronic tunneling, which are not obtained by coupling to a dark cavity, can already be realized with a single-photon state (no coherent states are needed). The analytic results are verified and extended with numerical simulations on a two-site Hubbard model coupled to a driven cavity mode. Our results generalize the well-established Floquet engineering of correlated electrons to the regime of quantum light. This opens up a pathway of controlling properties of quantum materials with high tunability and low energy dissipation.
CRIS-Team WoS Importer:2021-01-22

Quantum witness of a damped qubit with generalized measurements - Bojer, Manuel; Friedenberger, Alexander; Lutz, Eric (Journal of Physics Communications, 2019)
We evaluate the quantum witness based on the no-signaling-in-time condition of a damped two-level system for nonselective generalized measurements of varying strength. We explicitly compute its dependence on the measurement strength for a generic example. We find a vanishing derivative for weak measurements and an infinite derivative in the limit of projective measurements. The quantum witness is hence mostly insensitive to the strength of the measurement in the weak measurement regime and displays a singular, extremely sensitive dependence for strong measurements. We finally relate this behavior to that of the measurement disturbance defined in terms of the fidelity between pre-measurement and post-measurement states.
CRIS-Team WoS Importer:2019-07-09

Quarks and letters. Naturwissenschaften in der Literatur und Kultur der Gegenwart - Heydenreich, Aura; Mecke, Klaus (De Gruyter, 2015)
Fragen und Antworten der Hirnforschung, Quantenmechanik oder Evolutionstheorie gehen in Romane ein, und Physiker oder Biologen verwenden rhetorische Sprachbilder, um ihre Erkenntnisse zu vermitteln oder sogar erst zu generieren. Dass literarische und wissenschaftliche Interessen sich nicht nur überschneiden, sondern im Kern eins sind, das war zu Keplers, Lichtenbergs oder Goethes Zeiten noch selbstverständlich. Sie wieder allgemein so sichtbar zu machen, wie sie es für zahlreiche Autoren der Gegenwartsliteratur – etwa Richard Powers, Thomas Lehr oder Raoul Schrott – stets geblieben ist, daran arbeiten in einer ungewöhnlichen Kooperation die Erlanger Departments für Physik und für Germanistik im Forschungszentrum ELINAS. Die Beiträge der Reihe widmen sich einerseits naturwissenschaftlichen Themen in literarischen Texten – etwa in Romanen des Amerikaners Richard Powers, der Chinesin Can Hue oder des Deutschen Raoul Schrott. Sie beleuchten andererseits aber auch, welche Rolle Ästhetik in Literatur undNaturwissenschaften spiel

Quench dynamics in one-dimensional optomechanical arrays - Raeisi, Sadegh; Marquardt, Florian (Physical Review A, 2020)
Nonequilibrium dynamics induced by rapid changes of external parameters is relevant for a wide range of scenarios across many domains of physics. For waves in spatially periodic systems, quenches will alter the band structure and generate new excitations. In the case of topological band structures, defect modes at boundaries can be generated or destroyed when quenching through a topological phase transition. Here, we show that optomechanical arrays are a promising platform for studying such dynamics, as their band structure can be tuned temporally by a control laser. We study the creation of nonequilibrium optical and mechanical excitations in one-dimensional arrays, including a bosonic version of the Su-Schrieffer-Heeger model. These ideas can be transferred to other systems such as driven nonlinear cavity arrays.
CRIS-Team WoS Importer:2020-02-28

QuTiP-BoFiN: A bosonic and fermionic numerical hierarchical-equations-of-motion library with applications in light-harvesting, quantum control, and single-molecule electronics - Lambert, Neill; Raheja, Tarun; Cross, Simon; Menczel, Paul; Ahmed, Shahnawaz; Pitchford, Alexander; Burgarth, Daniel; Nori, Franco (Physical Review Research, 2023)
The "hierarchical equations of motion"(HEOM) method is a powerful exact numerical approach to solve the dynamics and find the steady-state of a quantum system coupled to a non-Markovian and nonperturbative environment. Originally developed in the context of physical chemistry, it has also been extended and applied to problems in solid-state physics, optics, single-molecule electronics, and biological physics. Here we present a numerical library in Python, integrated with the powerful QuTiP platform, which implements the HEOM for both bosonic and fermionic environments. We demonstrate its utility with a series of examples consisting of benchmarks against important known results and examples demonstrating insights gained with this library for this article. For the bosonic case, our results include demonstrations of how to fit arbitrary spectral densities with different approaches, and a study of the dynamics of energy transfer in the Fenna-Matthews-Olson photosynthetic complex. For the latter, we both clarify how a suitable non-Markovian environment can protect against pure dephasing, and model recent experimental results demonstrating the suppression of electronic coherence. Importantly, we show that by combining the HEOM method with the reaction coordinate method we can observe nontrivial system-environment entanglement on timescales substantially longer than electronic coherence alone. We also demonstrate results showing how the HEOM can be used to benchmark different strategies for dynamical decoupling of a system from its environment, and show that the Uhrig pulse-spacing scheme is less optimal than equally spaced pulses when the environment's spectral density is very broad. For the fermionic case, we present an integrable single-impurity example, used as a benchmark of the code, and a more complex example of an impurity strongly coupled to a single vibronic mode, with applications to single-molecule electronics.
CRIS-Team Scopus Importer:2023-04-14

Radial distribution function for semiflexible polymers confined in microchannels - Mecke, Klaus; et al. (EPL - Europhysics Letters, 2007)
An analytic expression is derived for the distribution G(R) of the end-to-end distance of semiflexible polymers in external potentials to elucidate the effect of confinement on the mechanical and statistical properties of biomolecules. For parabolic confinement the result is exact, whereas for realistic potentials a self-consistent ansatz is applied, so that G(R) is given explicitly even for hard-wall confinement. The theoretical result is in good quantitative agreement with fluorescence microscopy data for actin filaments confined in rectangularly shaped microchannels. This allows an unambiguous determination of persistence length LP and the dependence of statistical properties such as Odijk's deflection length lambda on the channel width D. It is shown that neglecting the effect of confinement leads to a significant overestimation of bending rigidities for. laments. Copyright (C) EPLA, 2007.

Radial Growth in 2D Revisited: The Effect of Finite Density, Binding Affinity, Reaction Rates, and Diffusion - Bihr, Timo; Sadafi, Fabrizio-Zagros; Smith, Ana-Suncana; Klupp Taylor, Robin; Seifert, Udo (Advanced Materials Interfaces, 2017)
Dendrite growth of metal patches on colloidal particles shows a variety of structures depending on the preparation conditions. The morphology of these patches suggests a cross-over from a reaction to a diffusion limited growth, implicating diffusion on the particle surface. Interestingly, the morphological and optical characteristics of the patches continuously change between two limiting behaviors. To understand this growth process, extensive simulations are performed, studying the fractal dimension and the dynamics of growth of a patch on a particle of a finite size, as a function of the initial density and the binding affinity of diffusing tracers. Several important growth regimes are characterized that enable to optimize the pathway for the synthesis of optically active, patchy particles.
Keywords: LIMITED AGGREGATION; CELL-ADHESION; FRACTAL AGGREGATION; COLLOIDAL SYNTHESIS; NANOSPHERES; DIMENSIONS; SIMULATION; NUCLEATION; PARTICLES; STABILITY

Radiofrequency ice dielectric measurements at Summit Station, Greenland - Aguilar, Juan Antonio; Allison, Patrick; Besson, Dave; Bishop, Abby; Botner, Olga; Bouma, Sjoerd; Buitink, Stijn; Cataldo, Maddalena; Clark, Brian A.; Couberly, Kenny; Curtis-Ginsberg, Zach; Dasgupta, Paramita; et al. (Journal of Glaciology, 2023)
We recently reported on the radio-frequency attenuation length of cold polar ice at Summit Station, Greenland, based on bi-static radar measurements of radio-frequency bedrock echo strengths taken during the summer of 2021. Those data also allow studies of (a) the relative contributions of coherent (such as discrete internal conducting layers with sub-centimeter transverse scale) vs incoherent (e.g. bulk volumetric) scattering, (b) the magnitude of internal layer reflection coefficients, (c) limits on signal propagation velocity asymmetries ('birefringence') and (d) limits on signal dispersion in-ice over a bandwidth of ∼100 MHz. We find that (1) attenuation lengths approach 1 km in our band, (2) after averaging 10 000 echo triggers, reflected signals observable over the thermal floor (to depths of ∼1500 m) are consistent with being entirely coherent, (3) internal layer reflectivities are ≈-60-70 dB, (4) birefringent effects for vertically propagating signals are smaller by an order of magnitude relative to South Pole and (5) within our experimental limits, glacial ice is non-dispersive over the frequency band relevant for neutrino detection experiments.
CRIS-Team Scopus Importer:2023-10-20
Keywords: Arctic glaciology; ice physics; radio-echo sounding

Raman response in antiferromagnetic two-leg S=1/2 Heisenberg ladders - Schmidt, Kai Phillip; et al. (EPL - Europhysics Letters, 2001)
The Raman response in the antiferromagnetic 2-leg S = 1/2 Heisenberg ladder is calculated for various couplings by continuous unitary transformations. For leg couplings above 80% of the rung coupling a characteristic 2-peak structure occurs with a point of zero intensity within the continuum. Experimental data for CaV2O5 and LayCa14-yCu24O41 are analyzed and the coupling constants are determined. Evidence is found that the Heisenberg model is not sufficient to describe cuprate ladders. We argue that a cyclic exchange term is the appropriate extension.

Raman response of magnetic excitations in cuprate ladders and planes - Schmidt, Kai Phillip; et al. (Physical Review B, 2005)
A unified picture for the Raman response of magnetic excitations in cuprate spin-ladder compounds is obtained by comparing calculated two-triplon Raman line shapes to those of the prototypical compounds SrCu2O3 (Sr123), Sr14Cu24O41 (Sr14), and La6Ca8Cu24O41 (La6Ca8). The theoretical model for the two-leg ladder contains Heisenberg exchange couplings J(parallel to) and J(perpendicular to) plus an additional four-spin interaction J(cyc). Within this model Sr123 and Sr14 can be described by x:=J(parallel to)/J(perpendicular to)=1.5, x(cyc):=J(cyc)/J(perpendicular to)=0.2, J(perpendicular to)(Sr123)=1130 cm(-1) and J(perpendicular to)(Sr14)=1080 cm(-1). The couplings found for La6Ca8 are x=1.2, x(cyc)=0.2, and J(perpendicular to)(La6Ca8)=1130 cm(-1). The unexpected sharp two-triplon peak in the ladder materials compared to the undoped two-dimensional cuprates can be traced back to the anisotropy of the magnetic exchange in rung and leg direction. With the results obtained for the isotropic ladder, we calculate the Raman line shape of a two-dimensional square lattice using a toy model consisting of a vertical and a horizontal ladder. A direct comparison of these results with Raman experiments for the two-dimensional cuprates R5CuO4(R=La,Nd), Sr2CuO2Cl2, and YBa2Cu3O6+delta yields a good agreement for the dominating two-triplon peak. We conclude that short-range quantum fluctuations are dominating the magnetic Raman response in both ladders and planes. We discuss possible scenarios responsible for the high-energy spectral weight of the Raman line shape, i.e., phonons, the triple-resonance, and multiparticle contributions.

Random walks with random velocities - Zaburdaev, Vasily; Schmiedeberg, Michael; Stark, Holger (Physical Review E, 2008)
We consider a random walk model that takes into account the velocity distribution of random walkers. Random motion with alternating velocities is inherent to various physical and biological systems. Moreover, the velocity distribution is often the first characteristic that is experimentally accessible. Here, we derive transport equations describing the dispersal process in the model and solve them analytically. The asymptotic properties of solutions are presented in the form of a phase diagram that shows all possible scaling regimes, including superdiffusive, ballistic, and superballistic motion. The theoretical results of this work are in excellent agreement with accompanying numerical simulation

Rapid Exploration of Topological Band Structures Using Deep Learning - Peano, Vittorio; Sapper, Florian; Marquardt, Florian (Physical Review X, 2021)
The design of periodic nanostructures allows to tailor the transport of photons, phonons, and matter waves for specific applications. Recent years have seen a further expansion of this field by engineering topological properties. However, what is missing currently are efficient ways to rapidly explore and optimize band structures and to classify their topological characteristics for arbitrary unit-cell geometries. In this work, we show how deep learning can address this challenge. We introduce an approach where a neural network first maps the geometry to a tight-binding model. The tight-binding model encodes not only the band structure but also the symmetry properties of the Bloch waves. This allows us to rapidly categorize a large set of geometries in terms of their band representations, identifying designs for fragile topologies. We demonstrate that our method is also suitable to calculate strong topological invariants, even when (like the Chern number) they are not symmetry indicated. Engineering of domain walls and optimization are accelerated by orders of magnitude. Our method directly applies to any passive linear material, irrespective of the symmetry class and space group. It is general enough to be extended to active and nonlinear metamaterials.
CRIS-Team Scopus Importer:2021-06-25

Reality conditions inducing transforms for quantum gauge field theory and quantum gravity - Thiemann, Thomas (Classical and Quantum Gravity, 1996)
We derive a canonical algorithm to obtain this holomorphic representation and in particular explicitly compute it for quantum gravity in terms of a Wick rotation transform.

Realizing quantum convolutional neural networks on a superconducting quantum processor to recognize quantum phases - Herrmann, Johannes; Llima, Sergi Masot; Remm, Ants; Zapletal, Petr; McMahon, Nathan; Scarato, Colin; Swiadek, Francois; Andersen, Christian Kraglund; Hellings, Christoph; Krinner, Sebastian; Lacroix, Nathan; Lazar, Stefania; et al. (Nature Communications, 2022)
Quantum neural networks could help analysing the output of quantum computers and quantum simulators of growing complexity. Here, the authors use a 7-qubit superconducting quantum processor to show how a quantum convolutional neural network can correctly recognise the phase of a quantum many-body state.
CRIS-Team WoS Importer:2022-07-29

Real-space cluster dynamical mean-field theory: Center-focused extrapolation on the one- and two particle-levels - Klett, Marcel; Wentzell, Nils; Schafer, Thomas; Simkovic, Fedor; Parcollet, Olivier; Andergassen, Sabine; Hansmann, Philipp (Physical Review Research, 2020)
We revisit the cellular dynamical mean-field theory (CDMFT) for the single-band Hubbard model on the square lattice at half filling, reaching real-space cluster sizes of up to 9 x 9 sites. Using benchmarks against direct lattice diagrammatic Monte Carlo at high temperature, we show that the self-energy obtained from a cluster center-focused extrapolation converges faster with the cluster size than the periodization schemes previously introduced in the literature. The same benchmark also shows that the cluster spin susceptibility can be extrapolated to the exact result at large cluster size, even though its spatial extension is larger than the cluster size.
CRIS-Team WoS Importer:2021-01-22

Recent Advances and Prospects in the Research of Nascent Adhesions - Stumpf, Henning; Ambriović-Ristov, Andreja; Radenovic, Aleksandra; Smith, Ana-Suncana (Frontiers in Physiology, 2020)
Nascent adhesions are submicron transient structures promoting the early adhesion of cells to the extracellular matrix. Nascent adhesions typically consist of several tens of integrins, and serve as platforms for the recruitment and activation of proteins to build mature focal adhesions. They are also associated with early stage signaling and the mechanoresponse. Despite their crucial role in sampling the local extracellular matrix, very little is known about the mechanism of their formation. Consequently, there is a strong scientific activity focused on elucidating the physical and biochemical foundation of their development and function. Precisely the results of this effort will be summarized in this article.
CRIS-Team Scopus Importer:2020-12-25
Keywords: focal adhesions; integrin activation; integrin clustering; modeling; nascent adhesions; superresolution microscopy

Reconstructing complex materials via effective grain shapes - Mecke, Klaus; et al. (Physical Review Letters, 2003)
We introduce a powerful method based on integral geometry and the Kac theorem for the spectrum of the Laplace operator to define the effective shape of an inclusion in a system made up of a distribution of arbitrarily shaped constituents. Reconstructing the microstructure using the effective inclusion shape leads to an excellent match to the percolation thresholds and to the mechanical and transport properties across all phase fractions. Use of the equivalent shape in effective medium formulations leads to good predictions. The method is verified for a sedimentary rock sample.

Reconstruction of complex materials by integral geometric measures - Mecke, Klaus (Journal of Materials Science & Technology, 2002)
The goal of much research in computational materials science is to quantify necessary morphological information and then to develop stochastic models which both accurately reflect the material morphology and allow one to estimate macroscopic physical properties. A novel method of characterizing the morphology of disordered systems is presented based on the evolution of a family of integral geometric measures during erosion and dilation operations. The method is used to determine the accuracy of model reconstructions of random systems. It is shown that the use of erosion/dilation operations on the original image leads to a more accurate discrimination of morphology than previous methods.
Keywords: porous media; integral geometry; morphology; erosion; dilation; Minkowski functionals; reconstruction

Reduced loop quantization with four Klein-Gordon scalar fields as reference matter - Giesel, Kristina; Vetter, Almut (Classical and Quantum Gravity, 2019)
We perform a reduced phase space quantization of gravity using four Klein-Gordon scalar fields as reference matter as an alternative to the Brown-Kuchar dust model in Giesel and Thiemann (2010 Class. Quantum Grav. 27 175009), where dust scalar fields are used. We compare our results to an earlier model by Domagala et al (2010 Phys. Rev. D 82 104038) where only one Klein-Gordon scalar field is considered as reference matter for the Hamiltonian constraint but the spatial diffeomorphism constraints are quantized using Dirac quantization. As a result we find that the choice of four conventional Klein-Gordon scalar fields as reference matter leads to a reduced dynamical model that cannot be quantized using loop quantum gravity techniques. However, we further discuss a slight generalization of the action for the four Klein-Gordon scalar fields and show that this leads to a model which can be quantized in the framework of loop quantum gravity. By comparison of the physical Hamiltonian operators obtained from the model by Domagala et al (2010 Phys. Rev. D 82 104038) and the one introduced in this work we are able to make a first step towards comparing Dirac and reduced phase space quantization in the context of the spatial diffeomorphism constraints.
CRIS-Team Scopus Importer:2019-08-02
Keywords: Dirac observables; loop quantum gravity; reduced phase space quantization

Reduced phase space approach to the U(1)3model for Euclidean quantum gravity - Bakhoda, S.; Thiemann, Thomas (Classical and Quantum Gravity, 2021)
If one replaces the constraints of the Ashtekar-Barbero SU(2) gauge theory formulation of Euclidean gravity by their U(1)3 version, one arrives at a consistent model which captures significant structure of its SU(2) version. In particular, it displays a non trivial realisation of the hypersurface deformation algebra which makes it an interesting testing ground for (Euclidean) quantum gravity as has been emphasised in a recent series of papers due to Varadarajan et al. In this paper we consider a reduced phase space approach to this model. This is especially attractive because, after a canonical transformation, the constraints are at most linear in the momenta. In suitable gauges, it is therefore possible to find a closed and explicit formula for the physical Hamiltonian which depends only on the physical observables. The corresponding reduced phase space quantisation can be confronted with the constraint quantisation due to Varadarajan et al to gain further insights into the quantum realisation of the hypersurface deformation algebra.
CRIS-Team Scopus Importer:2021-11-12
Keywords: asymptotically flat boundary conditions; gauge theory formulation of GR; quantum gravity; reduced phase space quantisation; U(1)3 model

Reduced phase space quantization and Dirac observables - Thiemann, Thomas (Classical and Quantum Gravity, 2006)
In her recent work, Dittrich generalized Rovelli's idea of partial observables to construct Dirac observables for constrained systems to the general case of an arbitrary first class constraint algebra with structure functions rather than structure constants. Here We use this framework and propose how to implement explicitly a reduced phase space quantization of a given system, at least in principle, without the need to Compute the gauge equivalence classes. The degree of practicality of this programme depends on the choice of the partial observables involved. The (multi-fingered) time evolution was shown to correspond to an automorphism on the set of Dirac observables, so generated and interesting representations of the latter will be those for which a suitable preferred Subgroup is realized unitarily. We sketch how Such a programme might look for general relativity. We also observe that the ideas by Dittrich can be used in order to generate constraints equivalent to those of the Hamiltonian constraints for general relativity such that they are spatially diffeomorphism invariant. This has the important Consequence that one can now quantize the new Hamiltonian constraints on the partially reduced Hilbert space of spatially diffeomorphism invariant states, just as for the recently proposed master constraint programme.

REDUCED PHASE-SPACE QUANTIZATION OF SPHERICALLY SYMMETRICAL EINSTEIN-MAXWELL THEORY INCLUDING A COSMOLOGICAL CONSTANT - Thiemann, Thomas (WORLD SCIENTIFIC PUBL CO PTE LTD, 1994)
We use the new canonical variables introduced by Ashtekar which simplifies the analysis tremendously.

Reduction in the surface energy of liquid interfaces at short length scales - Mecke, Klaus; et al. (Nature, 2000)
Liquid-vapour interfaces, particularly those involving water, are common in both natural and artificial environments. They were first described as regions of continuous variation of density(1), caused by density fluctuations within the bulk phases(2-4). In contrast, the more recent capillary-wave model(5,6) assumes a step-like local density profile across the liquid-vapour interface, whose width is the result of the propagation of thermally excited capillary waves. The model has been validated for length scales of tenths of micrometres and larger(7,8), but the structure of liquid surfaces on submicrometre length scales-where the capillary theory is expected to break down-remains poorly understood. Here we report grazing-incidence X-ray scattering experiments that allow for a complete determination of the free surface structure and surface energy for water and a range of organic liquids. We observe a large decrease of up to 75% in the surface energy of submicrometre waves that cannot be explained by capillary theory, but is in accord with the effects arising from the non-locality of attractive intermolecule interactions as predicted by a recent density functional theory(9), Our data, and the results of comparable measurements on liquid solutions, metallic alloys, surfactants, lipids and wetting films should thus provide a stringent test for any new theories that attempt to describe the structure of liquid interfaces with nanometre-scale resolution.

Regimes of motion of magnetocapillary swimmers - Sukhov, Alexander; Hubert, Maxime; Grosjean, Galien; Trosman, Oleg; Ziegler, Sebastian; Collard, Ylona; Vandewalle, Nicolas; Smith, Ana-Suncana; Harting, Jens (European Physical Journal E, 2021)
The dynamics of a triangular magnetocapillary swimmer is studied using the lattice Boltzmann method. We extend on our previous work, which deals with the self-assembly and a specific type of the swimmer motion characterized by the swimmer's maximum velocity centred around the particle's inverse viscous time. Here, we identify additional regimes of motion. First, modifying the ratio of surface tension and magnetic forces allows to study the swimmer propagation in the regime of significantly lower frequencies mainly defined by the strength of the magnetocapillary potential. Second, introducing a constant magnetic contribution in each of the particles in addition to their magnetic moment induced by external fields leads to another regime characterized by strong in-plane swimmer reorientations that resemble experimental observations.
CRIS-Team WoS Importer:2021-05-14

Relating dust reference models to conventional systems in manifestly gauge invariant perturbation theory - Giesel, Kristina; Li, Bao-Fei; Singh, Parampreet (Physical Review D - Particles, Fields, Gravitation and Cosmology, 2021)
Models with dust reference fields in relational formalism have proved useful in understanding the construction of gauge invariant perturbation theory to arbitrary orders in the canonical framework. These reference fields modify the dynamical equations for perturbation equations. However, important questions remain open on the relation with conventional perturbation theories of inflaton coupled to gravity and of multifluid systems, and on understanding modifications in terms of physical degrees of freedom. These gaps are filled in this manuscript for Brown-Kuchař and Gaussian dust models, both of which involve three scalar physical degrees of freedom. We establish a relationship of these models with conventional inflationary and multifluid systems of inflation and ordinary dust by introducing a set of gauge invariant variables on the reduced phase space of the dust reference models. We find the modifications due to dust clocks to the Bardeen equation in the longitudinal gauge and the Mukhanov-Sasaki equation in the spatially flat gauge, in terms of physical degrees of freedom. This results in a closed system of equations for all the degrees of freedom needed to explore the evolution of the scalar perturbations. Our analysis shows for the first time that even for two-fluid systems, there is a natural choice of the set of gauge invariant variables for each chosen gauge which not only offers a direct physical interpretation but also results in simplifications to the dynamical equations.<br
Keywords: Cosmology; Cosmological Perturbation Theory

Relation Between Regge Calculus and BF Theory on Manifolds with Defects - Kisielowski, Marcin (Annales Henri Poincaré, 2019)
In Regge calculus, the space–time manifold is approximated by certain abstract simplicial complex, called a pseudomanifold, and the metric is approximated by an assignment of a length to each 1-simplex. In this paper for each pseudomanifold, we construct a smooth manifold which we call a manifold with defects. This manifold emerges from the purely combinatorial simplicial complex as a result of gluing geometric realizations of its n-simplices followed by removing the simplices of dimension n- 2. The Regge geometry is encoded in a boundary data of a BF theory on this manifold. We consider an action functional which coincides with the standard BF action for suitably regular manifolds with defects and fields. We show that the action evaluated at solutions of the field equations satisfying certain boundary conditions coincides with an evaluation of the Regge action at Regge geometries defined by the boundary data. As a result, the degrees of freedom of Regge calculus are traded for discrete degrees of freedom of topological BF theory.
CRIS-Team Scopus Importer:2019-05-07

Representation of simultaneity in narrative media Or: How to circumvent time - Winter, Stefan (Concepts of Simultaneity, 2015)
The talk aims to give a short overview of how different media try to deal with simultaneity. The main focus concerns the techniques employed by the respective media to represent physical concepts of the present moment. This question led to the conception and writing of the experimental text z+x3+y6, which tackles the idea of simultaneity both visually and textually. Parts of the text and the ideas involved in its construction will be explored in the accompanying reading.
Keywords: OuLiPo; Experimental Literature; Postmodernism; Transmedia Studies

Resolving Hubble Tension with New Gravitational Scalar Tensor Theories - Banerjee, Shreya; Petronikolou, Maria; Saridakis, Emmanuel N. (Proceedings of Science, 2023)
We investigate the cosmological applications of new gravitational scalar-tensor theories and we analyze them in the light of H0 tension. In these theories the Lagrangian contains the Ricci scalar and its first and second derivatives in a specific combination that makes them free of ghosts, thus corresponding to healthy bi-scalar extensions of general relativity. We examine two specific models, and for particular choices of the model parameters we find that the effect of the additional terms is negligible at high redshifts, obtaining a coincidence with ΛCDM cosmology, however as time passes the deviation increases and thus at low redshifts the Hubble parameter acquires increased values (H0 ≈ 74km/s/Mpc) in a controlled way. The mechanism behind this behavior is the fact that the effective dark-energy equation-of-state parameter exhibits phantom behavior, which implies faster expansion, which is one of the theoretical requirements that are capable of alleviating the H0 tension. Lastly, we confront the models with Cosmic Chronometer (CC) data showing full agreement within 1σ confidence level.
CRIS-Team Scopus Importer:2023-12-15

Resonant electron transport in single-molecule junctions: Vibrational excitation, rectification, negative differential resistance, and local cooling - Härtle, Rainer; Thoss, Michael (Physical Review B, 2011)
Vibronic effects in resonant electron transport through single-molecule junctions are analyzed. The study is based on generic models for molecular junctions, which include electronic states on the molecular bridge that are vibrationally coupled and exhibit Coulomb interaction. The transport calculations employ a master equation approach. The results, obtained for a series of models with increasing complexity, show a multitude of interesting transport phenomena, including vibrational excitation, rectification, negative differential resistance, as well as local cooling. While some of these phenomena have been observed or proposed before, the present analysis extends previous studies and allows a more detailed understanding of the underlying transport mechanisms. In particular, it is shown that many of the observed phenomena can only be explained if electron-hole pair creation processes at the molecule-lead interface are taken into account. Furthermore, vibronic effects in systems with multiple electronic states and their role for the stability of molecular junctions are analyzed. © 2011 American Physical Society.
UnivIS-Import:2015-03-09:Pub.2011.nat.dphy.ITP.ppem.resona

Resonant Vibrations, Peak Broadening, and Noise in Single Molecule Contacts: The Nature of the First Conductance Peak - Secker, Daniel; Wagner, Stefan; Ballmann, Stefan Dieter; Härtle, Rainer; Thoss, Michael; Weber, Heiko B. (Physical Review Letters, 2011)
We carry out experiments on single-molecule junctions at low temperatures, using the mechanically controlled break junction technique. Analyzing the results obtained with various molecules, the nature of the first peak in the differential conductance spectra is elucidated. We observe an electronic transition with a vibronic fine structure, if the first peak occurs at small voltages. This regime can accurately be described by the resonant tunneling model. At higher voltages, additional smearing is observed and no fine structure can be resolved. A detailed analysis of the noise signal indicates that the onset of current is associated with strong fluctuations as a precursor of current flow. The data indicate that a complex fluctuation-driven transport mechanism takes over in this regime. © 2011 American Physical Society.
UnivIS-Import:2015-04-14:Pub.2011.nat.dphy.IAP.LAP.resona

Revealing Hund's multiplets in Mott insulators under strong electric fields - Dasari, Nagamalleswara Rao; Li, Jiajun; Werner, Philipp; Eckstein, Martin (Physical Review B, 2020)
We investigate the strong-field dynamics of a paramagnetic two-band Mott insulator using real-time dynamical mean-field theory. We demonstrate that strong electric fields can lead to a transient localization of electrons. This nonequilibrium quantum effect allows us to reveal specific signatures of local correlations in the time-resolved photoemission spectrum. In particular, we demonstrate that the localization can be strong enough to produce atomiclike spin multiplets determined by the Hund's coupling J, and thus provide a way of measuring J inside the solid. Our simulation also fully incorporates nonlinear field-induced tunneling processes, which would lead to a dielectric breakdown in the steady state limit. A careful analysis of these processes, however, shows that they remain weak enough and do not prevent the measurement of the transiently localized spectra.
CRIS-Team WoS Importer:2020-04-24

Revisiting a 4-Scalar Fields Reference Model in the Context of a Loop Quantization - Weigl, Stefan; Giesel, Kristina (Friedrich-Alexander-Universität Erlangen-Nürnberg, 2021)

Rhodomyrtals A-D, four unusual phloroglucinol-sesquiterpene adducts from Rhodomyrtus psidioides - Shou, Qingyao; Smith, Joshua E.; Mon, Htwe; Brkljaca, Zlatko; Smith, Ana-Suncana; Smith, David M.; Griesser, Hans J.; Wohlmuth, Hans (RSC Advances, 2014)
Four novel compounds, rhodomyrtals A-D (1-4), with two unprecendented carbon frameworks of phloroglucinol coupled eudesmane, together with the known compound eucalyptin A (5) have been isolated from the leaves of the Australian plant Rhodomyrtus psidioides. The structures of compounds 1-4 were elucidated by spectroscopic analysis and ECD calculations. Some of the compounds showed good antibacterial activity against selected Gram-positive strains.
Keywords: TOMENTOSA AITON HASSK.; STAPHYLOCOCCUS-AUREUS; EUCALYPTUS-GLOBULUS; MYRTACEAE; CANDIDATE; LEAVES

Rhombic Preordering on a Square Substrate - Neuhaus, Tim; Marechal, Mattheus; Schmiedeberg, Michael; Löwen, Hartmut (Physical Review Letters, 2013)
A competition of incommensurate symmetries occurs whenever a system is forced to conform to an ordering that is different from the intrinsically preferred structure of the system itself. As a model system of such a competition, we study the rivalry between the triangular ordering of hard disks and the square symmetry induced by a periodic square substrate. By using density functional theory as well as Monte Carlo computer simulations, we determine the full phase behavior for the case of one particle per minimum. We observe a rhombic preordering structure preceding the hexagonal solid as a direct consequence of the competing symmetries. Furthermore, the square-rhombic transition is reentrant with increasing substrate interaction. Our predictions can be verified in experiments of colloids in laser fields. DOI: 10.1103/PhysRevLett.110.118301

Roadmap on Spin-Wave Computing - Chumak, A. V.; Kabos, P.; Wu, M.; Abert, C.; Adelmann, C.; Adeyeye, A.; Akerman, J.; Aliev, F. G.; Anane, A.; Awad, A.; Back, C. H.; Barman, A.; et al. (IEEE Transactions on Magnetics, 2022)
Magnonics addresses the physical properties of spin waves and utilizes them for data processing. Scalability down to atomic dimensions, operation in the GHz-to-THz frequency range, utilization of nonlinear and nonreciprocal phenomena, and compatibility with CMOS are just a few of many advantages offered by magnons. Although magnonics is still primarily positioned in the academic domain, the scientific and technological challenges of the field are being extensively investigated, and many proof-of-concept prototypes have already been realized in laboratories. This roadmap is a product of the collective work of many authors that covers versatile spin-wave computing approaches, conceptual building blocks, and underlying physical phenomena. In particular, the roadmap discusses the computation operations with Boolean digital data, unconventional approaches like neuromorphic computing, and the progress towards magnon-based quantum computing. The article is organized as a collection of sub-sections grouped into seven large thematic sections. Each sub-section is prepared by one or a group of authors and concludes with a brief description of current challenges and the outlook of further development for each research direction.
CRIS-Team Scopus Importer:2022-02-25
Keywords: computing; data processing; Logic gates; Magnetic domains; magnon; magnonics; Magnonics; Nanoscale devices; Physics; Quantum computing; Spin wave; Three-dimensional displays

ROBUST MORPHOLOGICAL MEASURES FOR LARGE-SCALE STRUCTURE IN THE UNIVERSE - Mecke, Klaus; et al. (Astronomy & Astrophysics, 1994)
The method is numerically robust even for small samples, independent of statistical assumptions, and yields global as well as local morphological information. We illustrate the method by applying it to a Poisson process, a 'double-Poisson' process, and to the Abell catalogue of galaxy clusters.
Keywords: METHODS; STATISTICAL; COSMOLOGY; LARGE-SCALE STRUCTURE OF UNIVERSE

Robustness of a Perturbed Topological Phase - Dusuel, Sebastien; Kamfor, Michael; Orus, Roman; Schmidt, Kai Phillip; Vidal, Julien (Physical Review Letters, 2011)
We investigate the stability of the topological phase of the toric code model in the presence of a uniform magnetic field by means of variational and high-order series expansion approaches. We find that when this perturbation is strong enough, the system undergoes a topological phase transition whose first-or second-order nature depends on the field orientation. When this transition is of second order, it is in the Ising universality class except for a special line on which the critical exponent driving the closure of the gap varies continuously, unveiling a new topological universality class.

Robustness of a topological phase: Topological color code in a parallel magnetic field - Jahromi, Saeed S.; Kargarian, Mehdi; Masoudi, S. Farhad; Schmidt, Kai Phillip (Physical Review B, 2013)
The robustness of the topological color code, which is a class of error-correcting quantum codes, is investigated under the influence of a uniform magnetic field on the honeycomb lattice. Our study relies on two high-order series expansions using perturbative continuous unitary transformations in the limit of low and high fields, exact diagonalization, and a classical approximation. We show that the topological color code in a single parallel field is isospectral to the Baxter-Wu model in a transverse field on the triangular lattice. It is found that the topological phase is stable up to a critical field beyond which it breaks down to the polarized phase by a first-order phase transition. The results also suggest that the topological color code is more robust than the toric code in the parallel magnetic field. DOI: 10.1103/PhysRevB.87.094413

Robust Pore Size Analysis of Filamentous Networks from Three-Dimensional Confocal Microscopy - Mickel, Walter; Münster, Stefan; Jawerth, Louise M.; Vader, David A.; Weitz, David A.; Sheppard, Adrian P.; Mecke, Klaus; Fabry, Ben; Schröder-Turk, Gerd (Biophysical Journal, 2008)
We describe a robust method for determining morphological properties of. lamentous biopolymer networks, such as collagen or other connective tissue matrices, from confocal microscopy image stacks. Morphological properties including pore size distributions and percolation thresholds are important for transport processes, e. g., particle diffusion or cell migration through the extracellular matrix. The method is applied to fluorescently labeled fiber networks prepared from rat-tail tendon and calf-skin collagen, at concentrations of 1.2, 1.6, and 2.4 mg/ml. The collagen fibers form an entangled and branched network. The medial axes, or skeletons, representing the collagen fibers are extracted from the image stack by threshold intensity segmentation and distance-ordered homotopic thinning. The size of the fiuid pores as defined by the radii of largest spheres that fit into the cavities between the collagen fibers is derived from Euclidean distance maps and maximal covering radius transforms of the fluid phase. The size of the largest sphere that can traverse the fluid phase between the collagen fibers across the entire probe, called the percolation threshold, was computed for both horizontal and vertical directions. We demonstrate that by representing the fibers as the medial axis the derived morphological network properties are both robust against changes of the value of the segmentation threshold intensity and robust to problems associated with the point-spread function of the imaging system. We also provide empirical support for a recent claim that the percolation threshold of a fiber network is close to the fiber diameter for which the Euler index of the networks becomes zero.

Romane schreiben wäre eine Lösung. Über die Vernetzung von Naturwissenschaft und Literatur. Ulrich Woelk im Dialog zu »Freigang«, »Die Einsamkeit des Astronomen«, »Joana Mandelbrot und ich« - Heydenreich, Aura; Mecke, Klaus (Physik und Poetik. Produktionsästhetik und Werkgenese. Autorinnen und Autoren im Dialog, 2015)

Roton Minimum as a Fingerprint of Magnon-Higgs Scattering in Ordered Quantum Antiferromagnets - Powalski, M.; Uhrig, G. S.; Schmidt, Kai Phillip (Physical Review Letters, 2015)
A quantitative description of magnons in long-range ordered quantum antiferromagnets is presented which is consistent from low to high energies. It is illustrated for the generic S = 1/2 Heisenberg model on the square lattice. The approach is based on a continuous similarity transformation in momentum space using the scaling dimension as the truncation criterion. Evidence is found for significant magnon-magnon attraction inducing a Higgs resonance. The high-energy roton minimum in the magnon dispersion appears to be induced by strong magnon-Higgs scattering.

Rung-singlet phase of the S=(1)/(2) two-leg spin-ladder with four-spin cyclic exchange - Schmidt, Kai Phillip; et al. (Physical Review B, 2003)
Using continuous unitary transformations (CUTs) we calculate the one-triplet gap for the antiferromagnetic S = 1/2 two-leg spin ladder with additional four-spin exchange interactions in a high order series expansion about the limit of isolated rungs. By applying an efficient extrapolation technique we calculate the transition line between the rung-singlet phase and a spontaneously dimerized phase with dimers on the legs. Using this extrapolation technique we are able to analyze the crossover from strong rung coupling to weakly coupled chains.

Sb2Se3Thin-Film Growth by Solution Atomic Layer Deposition - Koch, Vanessa; Charvot, Jaroslav; Cao, Yuanyuan; Hartmann, Claudia; Wilks, Regan G.; Kundrata, Ivan; Minguez Bacho, Ignacio; Gheshlaghi, Negar; Hoga, Felix; Stubhan, Tobias; Alex, Wiebke; Pokorný, Daniel; et al. (Chemistry of Materials, 2022)
We establish solution atomic layer deposition (sALD) for the controlled growth of pure Sb2Se3 thin films under mild conditions, namely, room temperature and atmospheric pressure. Upscaling this process yields Sb2Se3 thin films with high homogeneity over large-area (4″) substrates. Annealing of the initially amorphous material leads to highly crystalline and smooth Sb2Se3 thin films. Removing the constraints of thermal stability and sufficient volatility in sALD compared to traditional gas-phase ALD opens up a broad choice of precursors and allows us to examine a wide range of Se2- precursors, of which some exhibit facile synthetic routes and allow us to tune their reactivity for optimal experimental ease of use. Moreover, we demonstrate that the solvent used in sALD represents an additional, attractive tool to influence and tailor the reactivity at the liquid-solid interface between the precursors and the surface.
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Scalar fields around a loop quantum gravity black hole in de Sitter spacetime: Quasinormal modes, late-time tails and strong cosmic censorship - Shao, Cai Ying; Zhang, Cong; Zhang, Wei; Shao, Cheng Gang (Physical Review D, 2024)
Loop quantum gravity, as one branch of quantum gravity, holds the potential to explore the fundamental nature of black holes. Recently, according to the quantum Oppenheimer-Snyder model in loop quantum cosmology, a novel loop quantum corrected black hole in de Sitter spacetime has been discovered. Here, we first investigate the corresponding quasinormal modes and late-time behavior of massless neutral scalar field perturbations based on such a quantum-modified black hole in de Sitter spacetime. The frequency and time domain analysis of the lowest-lying quasinormal modes is derived by the Prony method, the matrix method as well as Wentzel-Kramers-Brillouin approximation. The influences of loop quantum correction, the black hole mass ratio, and the cosmological constant on the quasinormal frequencies are studied in detail. The late-time behaviors of quantum-modified black holes possess an exponential decay, which is mainly determined not only by the multipole number but also by the cosmological constant. The impact of loop quantum correction on the late-time tail is negligible, but it has a significant impact on damping oscillation. To explore spacetime singularities, we examine the validity of strong cosmic censorship for a near-extremal quantum-modified black hole in de Sitter spacetime. As a result, it is found that the strong cosmic censorship is destroyed as the black hole approaches the near-extremal limit, but the violation becomes weaker as the cosmological constant and the loop quantum correction increase.
CRIS-Team Scopus Importer:2024-03-15

Scalar material reference systems and loop quantum gravity - Giesel, Kristina; Thiemann, Thomas (Classical and Quantum Gravity, 2015)
In the past, the possibility to employ (scalar) material reference systems in order to describe classical and quantum gravity directly in terms of gauge invariant (Dirac) observables has been emphasized frequently. This idea has been picked up more recently in loop quantum gravity with the aim to perform a reduced phase space quantization of the theory, thus possibly avoiding problems with the (Dirac) operator constraint quantization method for a constrained system. In this work, we review the models that have been studied on the classical and/or the quantum level and parametrize the space of theories considered so far. We then describe the quantum theory of a model that, to the best of our knowledge, has only been considered classically so far. This model could arguably be called the optimal one in this class of models considered as it displays the simplest possible true Hamiltonian, while at the same time reducing all constraints of general relativity.
Keywords: scalar material reference systems; loop quantum gravity; Dirac observables

Scaling at quantum phase transitions above the upper critical dimension - Langheld, Anja; Koziol, Jan; Adelhardt, Patrick; Kapfer, Sebastian; Schmidt, Kai Phillip (SciPost Physics, 2022)
The hyperscaling relation and standard finite-size scaling (FSS) are known to break down above the upper critical dimension due to dangerous irrelevant variables. We establish a coherent formalism for FSS at quantum phase transitions above the upper critical dimension following the recently introduced Q-FSS formalism for thermal phase transitions. Contrary to long-standing belief, the correlation sector is affected by dangerous irrelevant variables. The presented formalism recovers a generalized hyperscaling relation and FSS form. Using this new FSS formalism, we determine the full set of critical exponents for the long-range transverse-field Ising chain in all criticality regimes ranging from the nearest-neighbor to the long-range mean-field regime. For the same model, we also explicitly confirm the effect of dangerous irrelevant variables on the characteristic length scale.
CRIS-Team Scopus Importer:2022-12-02

Scaling in the time domain: Universal dynamics of order fluctuations in Fe3Al - Mecke, Klaus; et al. (Science, 2005)
By focusing a highly brilliant synchrotron x-ray beam to a micrometer spot on a sample, we measured in real time the x-ray intensity fluctuations associated with order fluctuations in crystalline materials. We applied this method to the binary alloy Fe3Al near its continuous A2-B2 phase transformation and determined a specific four-point time correlation function for the order parameter. From a detailed theoretical analysis, dynamical scaling in the time domain with a transition from noncritical to critical dynamics is disclosed.

Scallop Theorem and Swimming at the Mesoscale - Hubert, Maxime; Trosman, Oleg; Collard, Ylona; Sukhov, Alexander; Harting, Jens; Vandewalle, N.; Smith, Ana-Suncana (Physical Review Letters, 2021)
By comparing theoretical modeling, simulations, and experiments, we show that there exists a swimming regime at low Reynolds numbers solely driven by the inertia of the swimmer itself. This is demonstrated by considering a dumbbell with an asymmetry in coasting time in its two spheres. Despite deforming in a reciprocal fashion, the dumbbell swims by generating a nonreciprocal Stokesian flow, which arises from the asymmetry in coasting times. This asymmetry acts as a second degree of freedom, which allows the scallop theorem to be fulfilled at the mesoscopic scale.
CRIS-Team WoS Importer:2021-06-25

Science meets Fiction. Nano-Modellierungen: Poesie und Mikroskopie - Heydenreich, Aura; Mecke, Klaus (homunculus verlag, 2018)
Bilder von der Natur im 21. Jahrhundert – das müssen nicht mehr nur Bilder von Wäldern, Tieren oder dem Mond sein, sondern können auch Dinge und Lebewesen des Nanokosmos zeigen, ins Auge gefasst durch ein Mikroskop. Was aber würde ein literarisches Mikroskop zum Vorschein bringen? Diese Frage stellte das Exzellenzcluster Engineering of Advanced Materials (EAM), ein interdisziplinärer Forschungsverbund an der Friedrich- Alexander-Universität Erlangen-Nürnberg (FAU), der neuartige Hochleistungsmaterialien erforscht und entwickelt. Mit Texten von Maria Anne Anders, Victoria Bauer, Thora Engel, Tobias Falberg, Suzanne Fischer, Axel Görlach, Birgit Honikel, Ricarda Howe, Mathias Jeschke, Philipp Kampa, Michael Kanofsky, Christine Kappe, Michael Köhler, Kristiane Kondrat, Simone Kornappel, Petra Ina Lang, Friederike Langer, Ute Paul, Andreas Peukert, Stephan Roiss, Wolfgang Roth, Veronica Rummel-Damian, Tanja Rupel Tera, Franziska Ruprecht, Kirsten Sanders, Barbara Schibli, Claus-Peter Schmidt, Rolf Schönlau, Anna Stern, Marlies Strübbe-Tewes, Gerhard Stübner, Cornelia Travnicek, Dorothea Weinfurtner, Bernhard Winter, Melanie Wolf und Franziska Wotzinge

SEARCH FOR A CORRELATION BETWEEN ANTARES NEUTRINOS AND PIERRE AUGER OBSERVATORY UHECRs ARRIVAL DIRECTIONS - Adrian-Martinez, S.; Al Samarai, I.; Albert, A.; Andre, Michel; Anghinolfi, M.; Anton, Gisela; Anvar, S.; Ardid, Miguel; Astraatmadja, T.; Aubert, J-J.; Baret, B.; Basa, S.; et al. (Astrophysical Journal, 2013)
A multimessenger analysis optimized for a correlation of arrival directions of ultra-high energy cosmic rays (UHECRs) and neutrinos is presented and applied to 2190 neutrino candidate events detected in 2007-2008 by the ANTARES telescope and 69 UHECRs observed by the Pierre Auger Observatory between 2004 January 1 and 2009 December 31. No significant correlation is observed. Assuming an equal neutrino flux (E-2 energy spectrum) from all UHECR directions, a 90% CL upper limit on the neutrino flux of 5.0 x 10(-8) GeV cm(-2) s(-1) per source is derived.
Keywords: astroparticle physics; cosmic rays; neutrinos

SEARCH FOR COSMIC NEUTRINO POINT SOURCES WITH FOUR YEARS OF DATA FROM THE ANTARES TELESCOPE - Adrian-Martinez, S.; Al Samarai, I.; Albert, A.; Andre, Michel; Anghinolfi, M.; Anton, Gisela; Anvar, S.; Ardid, Miguel; Astraatmadja, T.; Aubert, J-J; Baret, B.; Basa, S.; et al. (Astrophysical Journal, 2012)
In this paper, a time-integrated search for point sources of cosmic neutrinos is presented using the data collected from 2007 to 2010 by the ANTARES neutrino telescope. No statistically significant signal has been found and upper limits on the neutrino flux have been obtained. Assuming an E-nu(-2). spectrum, these flux limits are at 1-10x10(-8) GeV cm(-2) s(-1) for declinations ranging from -90 degrees to 40 degrees. Limits for specific models of RX J1713.7-3946 and Vela X, which include information on the source morphology and spectrum, are also given.
Keywords: astroparticle physics; cosmic rays; neutrinos

Search for muon neutrinos from gamma-ray bursts with the ANTARES neutrino telescope using 2008 to 2011 data - Adrian-Martinez, S.; Albert, A.; Al Samarai, I.; Andre, Michel; Anghinolfi, M.; Anton, Gisela; Anvar, S.; Ardid, Miguel; Astraatmadja, T.; Aubert, J. -J.; Baret, B.; Barrios-Marti, J.; et al. (Astronomy & Astrophysics, 2013)
Aims. We search for muon neutrinos in coincidence with GRBs with the ANTARES neutrino detector using data from the end of 2007 to 2011.Methods. Expected neutrino fluxes were calculated for each burst individually. The most recent numerical calculations of the spectra using the NeuCosmA code were employed, which include Monte Carlo simulations of the full underlying photohadronic interaction processes. The discovery probability for a selection of 296 GRBs in the given period was optimised using an extended maximum-likelihood strategy.Results. No significant excess over background is found in the data, and 90% confidence level upper limits are placed on the total expected flux according to the model.
Keywords: neutrinos; gamma-ray burst: general; methods: numerical

Search for neutrino emission from gamma-ray flaring blazars with the ANTARES telescope - Adrian-Martinez, S.; Al Samarai, I.; Albert, A.; Andre, Michel; Anghinolfi, M.; Anton, Gisela; Anvar, S.; Ardid, Miguel; Astraatmadja, T.; Aubert, J-J.; Baret, B.; Basa, S.; et al. (Astroparticle Physics, 2012)
The ANTARES telescope is well-suited to detect neutrinos produced in astrophysical transient sources as it can observe a full hemisphere of the sky at all times with a high duty cycle. Radio-loud active galactic nuclei with jets pointing almost directly towards the observer, the so-called blazars, are particularly attractive potential neutrino point sources. The all-sky monitor LAT on board the Fermi satellite probes the variability of any given gamma-ray bright blazar in the sky on time scales of hours to months. Assuming hadronic models, a strong correlation between the gamma-ray and the neutrino fluxes is expected. Selecting a narrow time window on the assumed neutrino production period can significantly reduce the background.An unbinned method based on the minimization of a likelihood ratio was applied to a subsample of data collected in 2008 (61 days live time). By searching for neutrinos during the high state periods of the AGN light curve, the sensitivity to these sources was improved by about a factor of two with respect to a standard time-integrated point source search. First results on the search for neutrinos associated with ten bright and variable Fermi sources are presented. (C) 2012 Elsevier B.V. All rights reserved.
Keywords: ANTARES; Neutrino astronomy; Fermi LAT transient sources; Time-dependent search; Blazars

Search for relativistic magnetic monopoles with the ANTARES neutrino telescope - Adrian-Martinez, S.; Aguilar, J. A.; Al Samarai, I.; Albert, A.; Andre, Michel; Anghinolfi, M.; Anton, Gisela; Anvar, S.; Ardid, Miguel; Jesus, A. C. Assis; Astraatmadja, T.; Aubert, J-J.; et al. (Astroparticle Physics, 2012)
Magnetic monopoles are predicted in various unified gauge models and could be produced at intermediate mass scales. Their detection in a neutrino telescope is facilitated by the large amount of light emitted compared to that from muons. This paper reports on a search for upgoing relativistic magnetic monopoles with the ANTARES neutrino telescope using a data set of 116 days of live time taken from December 2007 to December 2008. The one observed event is consistent with the expected atmospheric neutrino and muon background, leading to a 90% C.L. upper limit on the monopole flux between 1.3 x 10-(17) and 8.9 x 10(-17) CM-2 s(-1) sr(-1) for monopoles with velocity beta >= 0.625. (c) 2012 Elsevier B.V. All rights reserved.
Keywords: Magnetic monopole; Neutrino telescopes; ANTARES

Second-order analysis by variograms for curvature measures of two-phase structures - Mecke, Klaus; et al. (European Physical Journal B, 2005)
Second-order characteristics are important in the description of various geometrical structures occurring in foams, porous media, complex fluids, and phase separation processes. The classical second order characteristics are pair correlation functions, which are well-known in the context of point fields and mass distributions. This paper studies systematically these and further characteristics from a unified standpoint, based on four so-called curvature measures, volume, surface area, integral of mean curvature and Euler characteristic. Their statistical estimation is straightforward only in the case of the volume measure, for which the pair correlation function is traditionally called the two-point correlation function. For the other three measures a statistical method is described which yields smoothed surrogates for pair correlation functions, namely variograms. Variograms lead to an enhanced understanding of the variability of the geometry of two-phase structures and can help in finding suitable models. The use of the statistical method is demonstrated for simulated samples related to Poisson-Voronoi tessellations, for experimental 3D images of Fontainebleau sandstone and for two samples of industrial foams.

Segal-Bargmann transforms from hyperbolic Hamiltonians - Kirwin, William D.; Mourão, José; Nunes, João P.; Thiemann, Thomas (Journal of Mathematical Analysis and Applications, 2021)
We consider the imaginary time flow of a quadratic hyperbolic Hamiltonian on the symplectic plane, apply it to the Schrödinger polarization and study the corresponding evolution of polarized sections. The flow is periodic in imaginary time and the evolution of polarized sections has interesting features. On the time intervals for which the polarization is real or Kähler, the half–form corrected time evolution of polarized sections is given by unitary operators which turn out to be equivalent to the classical Segal-Bargmann transforms (which are usually associated to the quadratic elliptic Hamiltonian [Formula presented] and to the heat operator). At the right endpoint of these intervals, the evolution of polarized sections is given by the Fourier transform from the Schrödinger to the momentum representation. In the complementary intervals of imaginary time, the polarizations are anti–Kähler and the Hilbert space of polarized sections collapses to H=0. Hyperbolic quadratic Hamiltonians thus give rise to a new factorization of the Segal-Bargmann transform, which is very different from the usual one, where one first applies a bounded contraction operator (the heat kernel operator), mapping L2–states to real analytic functions with unique analytic continuation, and then one applies analytic continuation. In the factorization induced by an hyperbolic complexifier, both factors are unbounded operators but their composition is, in the Kähler or real sectors, unitary. In another paper [24], we explore the application of the above family of unitary transforms to the definition of new holomorphic fractional Fourier transforms.
CRIS-Team Scopus Importer:2021-05-14
Keywords: Geometric quantization; Hamiltonian flows in imaginary time; Segal-Bargmann transform

SEGREGATION PROFILES IN CU3AU ABOVE THE ORDER-DISORDER TRANSITION - Mecke, Klaus; et al. (Physical Review B, 1995)
The segregation at a (100) surface of Cu3Au is studied slightly above the order-disorder transition at T-c. Based on a semi-infinite lattice-gas model with nearest- and next-nearest-neighbor interactions, we find within mean-field theory that close to the surface and in the disordered phase the Au concentration decays exponentially towards its bulk value. The corresponding decay length Lambda increases as (T-T-sp)(-1/2) upon approaching T-c, where T-sp < T-c denotes the spinodal temperature of the order-disorder transition. Without using any adjustable parameters, we obtain theoretical predictions in good quantitative agreement with recent x-ray-scattering data from this surface.

Self-assembly and entropic effects in pear-shaped colloid systems. II. Depletion attraction of pear-shaped particles in a hard-sphere solvent - Schönhöfer, Philipp W.A.; Marechal, Mattheus; Cleaver, Douglas J.; Schröder-Turk, Gerd E. (Journal of Chemical Physics, 2020)
We consider depletion effects of a pear-shaped colloidal particle in a hard-sphere solvent for two different model realizations of the pear-shaped colloidal particle. The two models are the pear hard Gaussian overlap (PHGO) particles and the hard pears of revolution (HPR). The motivation for this study is to provide a microscopic understanding for the substantially different mesoscopic self-assembly properties of these pear-shaped colloids, in dense suspensions, that have been reported in the previous studies. This is done by determining their differing depletion attractions via Monte Carlo simulations of PHGO and HPR particles in a pool of hard spheres and comparing them with excluded volume calculations of numerically obtained ideal configurations on the microscopic level. While the HPR model behaves as predicted by the analysis of excluded volumes, the PHGO model showcases a preference for splay between neighboring particles, which can be attributed to the special non-additive characteristics of the PHGO contact function. Lastly, we propose a potentially experimentally realizable pear-shaped particle model, the non-additive hard pear of revolution model, which is based on the HPR model but also features non-additive traits similar to those of PHGO particles to mimic their depletion behavior.
CRIS-Team Scopus Importer:2020-08-07

Self-assembly and entropic effects in pear-shaped colloid systems. I. Shape sensitivity of bilayer phases in colloidal pear-shaped particle systems - Schönhöfer, Philipp W.A.; Marechal, Mattheus; Cleaver, Douglas J.; Schröder-Turk, Gerd E. (Journal of Chemical Physics, 2020)
The role of particle shape in self-assembly processes is a double-edged sword. On the one hand, particle shape and particle elongation are often considered the most fundamental determinants of soft matter structure formation. On the other hand, structure formation is often highly sensitive to details of shape. Here, we address the question of particle shape sensitivity for the self-assembly of hard pear-shaped particles by studying two models for this system: (a) the pear hard Gaussian overlap (PHGO) and (b) the hard pears of revolution (HPR) model. Hard pear-shaped particles, given by the PHGO model, are known to form a bicontinuous gyroid phase spontaneously. However, this model does not replicate an additive object perfectly and, hence, varies slightly in shape from a "true" pear-shape. Therefore, we investigate in the first part of this series the stability of the gyroid phase in pear-shaped particle systems. We show, based on the HPR phase diagram, that the gyroid phase does not form in pears with such a "true" hard pear-shaped potential. Moreover, we acquire first indications from the HPR and PHGO pair-correlation functions that the formation of the gyroid is probably attributed to the small non-additive properties of the PHGO potential.
CRIS-Team Scopus Importer:2020-08-07

Self-assembly of complex structures in colloid-polymer mixtures - Oğuz, Erdal; Mijailović, Aleksandar; Schmiedeberg, Michael (Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 2018)
If particles interact according to isotropic pair potentials that favor multiple length scales, in principle, a large variety of different complex structures can be achieved by self-assembly. Here, we study the specific example of colloid-polymer mixtures in which the effective interactions between colloids are dictated by a Aasakura-Osawa–type potential that possesses two length scales. Upon examining the phase behavior of two-dimensional colloid-polymer mixtures, we observe that nontrivial structures only occur in the vicinity of selected densities where triangular ordering is suppressed by the pair potential. Close to these densities, a large number of different phases self-assemble that correspond to tilings containing triangular, rhombic, square, hexagonal, and pentagonal tiles, and including some of the Archimedean tilings. We obtain the ground-state energies by minimizing the corresponding lattice sums with respect to particle positions in a unit cell as well as cell geometry and verify the occurrence of selected phases at finite temperatures by using Brownian dynamics simulations. We explain how the occurrence of nontrivial orderings can be predicted on a two-particle level by employing an enthalpylike pair potentials. Our work provides a manual on how to find the regions of nontrivial phases in parameter space for complex pair interactions in genera

Self-consistent mean-field description of nuclear structure and dynamics-a status report - Erler, J.; Kleinig, W.; Klüpfel, P.; Kvasil, J.; Nesterenko, V. O.; Reinhard, Paul-Gerhard (Physics of Particles and Nuclei, 2010)
This contribution deals with the predictive power of the Skyrme-Hartree-Fock model. First, we discuss the phenomenological adjustment of the Skyrme energy-functional and the choice of proper fit data. Then, we check the reliability in extrapolations to other observables and nuclei, using two strategies: first, comparison with data for observables not included in the fit, and second, an estimate of the extrapolation error by virtue of the least-squares fitting techniques. Test cases will be energies of extremely neutron rich Sn isotopes as well as energies, giant resonances, and fission properties of super-heavy elements. © 2010 Pleiades Publishing, Ltd.
CRIS-Team Scopus Importer:2023-07-24

Self-consistent nuclear mean-field models: Example Skyrme-Hartree-Fock - Erler, J.; Klüpfel, P.; Reinhard, Paul-Gerhard (Journal of Physics G: Nuclear and Particle Physics, 2011)
We review recent developments in the Skyrme-Hartree-Fock (SHF) approach for a self-consistent description of nuclear ground-state properties and dynamics. A brief summary of the Skyrme energy functional and additional ingredients (pairing, Coulomb, center-of-mass correction) is given. Strategies for phenomenological calibration of the SHF functional are discussed. Applications to a variety of observables are presented: the bulk properties of nuclei (energy, charge radius, surface thickness), the impact of information on neutron radii, extrapolation to super-heavy elements and fission stability thereof, isotopic shifts of radii, odd nuclei and associated single-nucleon spectra, low-lying surface vibrations together with the ground-state correlations associated with them, and giant resonances (electric as well as magnetic modes). © 2011 IOP Publishing Ltd.
CRIS-Team Scopus Importer:2023-07-24

Self-duality and bound states of the toric code model in a transverse field - Vidal, Julien; Thomale, Ronny; Schmidt, Kai Phillip; Dusuel, Sebastien (Physical Review B, 2009)
We investigate the effect of a transverse magnetic field on the toric code model. We show that this problem can be mapped onto the Xu-Moore model and thus onto the quantum compass model, which are known to be self-dual. We analyze the low-energy spectrum by means of perturbative continuous unitary transformations and determine accurately the energy gaps of various symmetry sectors. Our results are in very good agreement with exact diagonalization data for all values of the parameters except at the self-dual point where level crossings are responsible for a first-order phase transition between a topological phase and a polarized phase. Interestingly, bound states of two and four quasiparticles with fermionic and bosonic statistics emerge, and display dispersion relations of reduced dimensionality.
Keywords: bound states; energy gap; fermion systems; magnetic transitions; perturbation theory; quasiparticles

Self-healing of Bessel beams - Lindlein, Norbert; Merklein, Bastian; Aiello, Andrea (2016)

Semi-Automatic Cell Correspondence Analysis Using Iterative Point Cloud Registration - Chen, Shuqing; Gehrer, Simone; Kaliman, Sara; Ravikumar, Nishant; Becit, Abdurrahman; Aliee, Maryam; Dudziak, Diana; Merkel, Rudolf; Smith, Ana-Suncana; Maier, Andreas (Bildverarbeitung für die Medizin 2019. Informatik aktuell., 2019)

Semiclassical behavior of spinfoam amplitude with small spins and entanglement entropy - Han, Muxin (Physical Review D, 2019)
Spinfoam amplitudes with small spins can have interesting semiclassical behavior and relate to semiclassical gravity and geometry in four dimensions. We study the generalized spinfoam model [spinfoams for all loop quantum gravity (LQG) [Kaminski et al., Spin-foams for all loop quantum gravity, Classical Quantum Gravity 27, 095006 (2010); Erratum, Classical Quantum Gravity 29, 049502(E) (2012), Ding et al., Generalized spinfoams, Phys. Rev. D 83, 124020 (2011)] with small spins j but a large number of spin degrees of freedom (d.o.f.), and find that it relates to the simplicial Engle-Pereira-Rovelli-Livine-Freidel-Krasnov model with large spins and Regge calculus by coarse-graining spin d.o.f. Small-j generalized spinfoam amplitudes can be employed to define semiclassical states in the LQG kinematical Hilbert space. Each of these semiclassical states is determined by a four-dimensional Regge geometry. We compute the entanglement Renyi entropies of these semiclassical states. The entanglement entropy interestingly coarse grains spin d.o.f. in the generalized spinfoam model, and satisfies an analog of the thermodynamical first law. This result possibly relates to the quantum black hole thermodynamics in [Ghosh and Perez, Black Hole Entropy and Isolated Horizons Thermodynamics, Phys. Rev. Lett. 107, 241301 (2011); 108, 169901(E) (2012)].
CRIS-Team WoS Importer:2019-11-01

Semiclassical Dynamics of Loop Quantum Gravity - Vetter, Almut (Friedrich-Alexander-Universität Erlangen-Nürnberg, 2022)

Semiclassical Perturbation Theory within Loop Quantum Gravity - Winnekens, David; Giesel, Kristina (Friedrich-Alexander-Universität Erlangen-Nürnberg, 2014)

Series expansions in closed and open quantum many-body systems with multiple quasiparticle types - Lenke, Lea; Schellenberger, Andreas; Schmidt, Kai Phillip (Physical Review A, 2023)
The established approach of perturbative continuous unitary transformations (pCUTs) constructs effective quantum many-body Hamiltonians as perturbative series that conserve the number of one quasiparticle type. We extend the pCUT method to similarity transformations - dubbed pcst++ - allowing for multiple quasiparticle types with complex-valued energies. This enlarges the field of application to closed and open quantum many-body systems with unperturbed operators corresponding to arbitrary superimposed ladder spectra. To this end, a generalized counting operator is combined with the quasiparticle generator for open quantum systems recently introduced by Schmiedinghoff and Uhrig [G. Schmiedinghoff and G. S. Uhrig, SciPost Phys. 13, 122 (2022)2542-465310.21468/SciPostPhys.13.6.122]. The pcst++ then yields model-independent block-diagonal effective Hamiltonians and Lindbladians, allowing a linked-cluster expansion in the thermodynamic limit similar to the conventional pCUT method. We illustrate the application of the pcst++ method by discussing representative closed, open, and non-Hermitian quantum systems.
CRIS-Team Scopus Importer:2023-08-18

Setting the pace of microswimmers: when increasing viscosity speeds up self-propulsion - Pande, Jayant; Merchant, Laura; Kruger, Timm; Harting, Jens; Smith, Ana-Suncana (New Journal of Physics, 2017)
It has long been known that some microswimmers seem to swim counter-intuitively faster when the viscosity of the surrounding fluid is increased, whereas others slow down. This conflicting dependence of the swimming velocity on the viscosity is poorly understood theoretically. Here we explain that any mechanical microswimmer with an elastic degree of freedom in a simple Newtonian fluid can exhibit both kinds of response to an increase in the fluid viscosity for different viscosity ranges, if the driving is weak. The velocity response is controlled by a single parameter Gamma, the ratio of the relaxation time of the elastic component of the swimmer in the viscous fluid and the swimming stroke period. This defines two velocity-viscosity regimes, which we characterize using the bead-spring microswimmer model and analyzing the different forces acting on the parts of this swimmer. The analytical calculations are supported by lattice-Boltzmann simulations, which accurately reproduce the two velocity regimes for the predicted values of Gamma.
Keywords: microswimming; anomalous increase in velocity; analytical modeling; lattice-Boltzmann simulations

Set Voronoi diagrams of 3D assemblies of aspherical particles - Schaller, Fabian M.; Kapfer, Sebastian C.; Evans, Myfanwy; Hoffmann, Matthias; Aste, Tomaso; Saadatfar, Mohammad; Mecke, Klaus; Delaney, Gary W.; Schröder-Turk, Gerd (TAYLOR & FRANCIS LTD, 2013)
Several approaches to quantitative local structure characterization for particulate assemblies, such as structural glasses or jammed packings, use the partition of space provided by the Voronoi diagram. The conventional construction for spherical mono-disperse particles, by which the Voronoi cell of a particle is that of its centre point, cannot be applied to configurations of aspherical or polydisperse particles. Here, we discuss the construction of a Set Voronoi diagram for configurations of aspherical particles in three-dimensional space. The Set Voronoi cell of a given particle is composed of all points in space that are closer to the surface (as opposed to the centre) of the given particle than to the surface of any other; this definition reduces to the conventional Voronoi diagram for the case of mono-disperse spheres. An algorithm for the computation of the Set Voronoi diagram for convex particles is described, as a special case of a Voronoi-based medial axis algorithm, based on a triangulation of the particles' bounding surfaces. This algorithm is further improved by a pre-processing step based on morphological erosion, which improves the quality of the approximation and circumvents the problems associated with small degrees of particle-particle overlap that may be caused by experimental noise or soft potentials. As an application, preliminary data for the volume distribution of disordered packings of mono-disperse oblate ellipsoids, obtained from tomographic imaging, is computed.
Keywords: Set Voronoi diagram; ellipsoid packings; random close packing; aspherical particles; medial axes and surfaces; Area Voronoi diagram; navigation map; skeleton by zone of influence

Shadow and stability of quantum-corrected black holes - Yang, Jinsong; Zhang, Cong; Ma, Yongge (European Physical Journal C: Particles and Fields, 2023)
Recently the quantum Oppenheimer–Snyder gravitational collapse model has been proposed in loop quantum gravity, providing quantum-corrected Schwarzschild spacetimes as the exterior of the collapsing dust ball. In this paper, the quantum gravity effects on the black hole shadows in this model are studied, and the stability of the quantum-corrected black holes is also analyzed by calculating the quasinormal modes. It turns out that the quantum correction always shrinks the radius of shadows, and the quantum-corrected black holes are stable against the scalar and vector perturbations.
CRIS-Team Scopus Importer:2023-07-28

Shear-induced slab-like domains in a directed percolated colloidal gel - Kohl, Matthias; Schmiedeberg, Michael (European Physical Journal E, 2017)

Shortcomings of the bond orientational order parameters for the analysis of disordered particulate matter - Mickel, Walter; Kapfer, Sebastian; Schröder-Turk, Gerd; Mecke, Klaus (Journal of Chemical Physics, 2013)
Local structure characterization with the bond-orientational order parameters q(4), q(6), ... introduced by Steinhardt et al. [Phys. Rev. B 28, 784 (1983)] has become a standard tool in condensed matter physics, with applications including glass, jamming, melting or crystallization transitions, and cluster formation. Here, we discuss two fundamental flaws in the definition of these parameters that significantly affect their interpretation for studies of disordered systems, and offer a remedy. First, the definition of the bond-orientational order parameters considers the geometrical arrangement of a set of nearest neighboring (NN) spheres, NN(p), around a given central particle p; we show that the choice of neighborhood definition can have a bigger influence on both the numerical values and qualitative trend of q(l) than a change of the physical parameters, such as packing fraction. Second, the discrete nature of neighborhood implies that NN(p) is not a continuous function of the particle coordinates; this discontinuity, inherited by q(l), leads to a lack of robustness of the q(l) as structure metrics. Both issues can be avoided by a morphometric approach leading to the robust Minkowski structure metrics q(l)'. These q(l)' are of a similar mathematical form as the conventional bond-orientational order parameters and are mathematically equivalent to the recently introduced Minkowski tensors [G. E. Schroder-Turk et al., Europhys. Lett. 90, 34001 (2010); S. Kapfer et al., Phys. Rev. E 85, 030301(R) (2012)]. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4774084]

Signature of a Nonharmonic Potential as Revealed from a Consistent Shape and Fluctuation Analysis of an Adherent Membrane - Schmidt, Daniel; Monzel, Cornelia; Bihr, Timo; Merkel, Rudolf; Seifert, Udo; Sengupta, Kheya; Smith, Ana-Suncana (Physical Review X, 2014)
The interaction of fluid membranes with a scaffold, which can be a planar surface or a more complex structure, is intrinsic to a number of systems from artificial supported bilayers and vesicles to cellular membranes. In principle, these interactions can be either discrete and protein mediated, or continuous. In the latter case, they emerge from ubiquitous intrinsic surface interaction potentials as well as nature-designed steric contributions of the fluctuating membrane or from the polymers of the glycocalyx. Despite the fact that these nonspecific potentials are omnipresent, their description has been a major challenge from experimental and theoretical points of view. Here, we show that a full understanding of the implications of the continuous interactions can be achieved only by expanding the standard superposition models commonly used to treat these types of systems, beyond the usual harmonic level of description. Supported by this expanded theoretical framework, we present three independent, yet mutually consistent, experimental approaches to measure the interaction potential strength and the membrane tension. Upon explicitly taking into account the nature of shot noise as well as the nature of finite experimental resolution, excellent agreement with the augmented theory is obtained, which finally provides a coherent view of the behavior of the membrane in the vicinity of a scaffold.
Keywords: INTERFERENCE CONTRAST MICROSCOPY; FLUID MEMBRANES; BENDING ELASTICITY; LIPID-BILAYERS; CELL-ADHESION; BROWNIAN-MOTION; DYNAMICS; VESICLES; BIOMEMBRANES; MECHANICS

Simplicial graviton from selfdual Ashtekar variables - Wieland, Wolfgang (Classical and Quantum Gravity, 2024)
In perturbative gravity, it is straight-forward to characterize the two local degrees of freedom of the gravitational field in terms of a mode expansion of the linearized perturbation. In the non-perturbative regime, we are in a more difficult position. It is not at all obvious how to construct Dirac observables that can separate the gauge orbits. Standard procedures rely on asymptotic boundary conditions or formal Taylor expansions of relational observables. In this paper, we lay out a new non-perturbative lattice approach to tackle the problem in terms of Ashtekar’s self-dual formulation. Starting from a simplicial decomposition of space, we introduce a local kinematical phase space at the lattice sites. At each lattice site, we introduce a set of constraints that replace the generators of the hypersurface deformation algebra in the continuum. We show that the discretized constraints close under the Poisson bracket. The resulting reduced phase space describes two complex physical degrees of freedom representing the two radiative modes at the discretized level. The paper concludes with a discussion of the key open problems ahead and the implications for quantum gravity.
CRIS-Team Scopus Importer:2024-02-02
Keywords: Hamiltonian formalism of general relativity; lattice methods; quantum gravity; selfdual gravity; spinfoams and loop quantum gravity

Simplification of the spectral analysis of the volume operator in loop quantum gravity - Brunnemann, Johannes; Thiemann, Thomas (Classical and Quantum Gravity, 2006)
The volume operator plays a crucial role in the definition of the quantum dynamics Of loop quantum gravity (LQG). Efficient calculations for dynamical problems of LQG can therefore be performed only if one has sufficient control over the Volume spectrum. While closed formulae for the matrix elements are currently available in the literature, these are complicated polynomials in 6j symbols which ill turn are given in terms of Racah's formula which is too complicated in order to perform even numerical calculations for the semiclassically important regime of large spins. Hence, so far Hot even numerically the spectrum could be accessed. In this paper, we demonstrate that by means of the Elliot-Biedenharn identify one can get rid of all the 6j symbols for any valence of: the gauge-invariant vertex, thus immensely reducing the computational effort. We use the resulting compact formula to study numerically the spectrum of the gauge-invariant 4-vertex. The techniques derived in this paper-could also be of use for the analysis of spin-spin interaction Hamiltonians of many-particle problems in atomic and nuclear physics.

Simulating stochastic geometries: morphology of overlapping grains - Mecke, Klaus; et al. (ELSEVIER SCIENCE BV, 2002)
Integral geometry furnishes a family of morphological descriptors known as Minkowski functionals which are related to curvature integrals. We present an exact algorithm for the calculation of Minkowski functionals for overlapping grains each with arbitrary location, orientation and shape (Boolean model). The method is numerically robust even for small samples, independent of statistical assumptions, and yields global as well as local morphological information. We illustrate the method by applying it to distributions of overlapping and hard disks. (C) 2002 Elsevier Science B.V All rights reserved.

Simulation of a hard-spherocylinder liquid crystal with the pe - Fischermeier, Ellen; Bartuschat, Dominik; Preclik, Tobias; Marechal, Mattheus; Mecke, Klaus (Computer Physics Communications, 2014)
The pe physics engine is validated through the simulation of a liquid crystal model system consisting of hard spherocylinders. For this purpose we evaluate several characteristic parameters of this system, namely the nematic order parameter, the pressure, and the Frank elastic constants. We compare these to the values reported in literature and find a very good agreement, which demonstrates that the pe physics engine can accurately treat such densely packed particle systems. Simultaneously we are able to examine the influence of finite size effects, especially on the evaluation of the Frank elastic constants, as we are far less restricted in system size than earlier simulations.
UnivIS-Import:2015-03-09:Pub.2014.tech.IMMD.lsinfs.simula_0
Keywords: Frank elastic constants; Hard rod; Liquid crystal; Parallel framework; Rigid body dynamics

Simulation of charge transport in organic semiconductors: A time-dependent multiscale method based on nonequilibrium Green's functions - Leitherer, Susanne; Jager, C. M.; Krause, Andreas; Halik, Marcus; Clark, Timothy; Thoss, Michael (Physical Review Materials, 2017)
In weakly interacting organic semiconductors, static disorder and dynamic disorder often have an important impact on transport properties. Describing charge transport in these systems requires an approach that correctly takes structural and electronic fluctuations into account. Here, we present a multiscale method based on a combination of molecular-dynamics simulations, electronic-structure calculations, and a transport theory that uses time-dependent nonequilibrium Green's functions. We apply the methodology to investigate charge transport in C-60-containing self-assembled monolayers, which are used in organic field-effect transistors.

Simulation of time-dependent resonant inelastic x-ray scattering using nonequilibrium dynamical mean-field theory - Eckstein, Martin; Werner, Philipp (Physical Review B, 2021)
We develop a framework to evaluate the time-dependent resonant inelastic x-ray scattering (RIXS) signal with the use of nonequilibrium dynamical mean-field theory simulations. The approach is based on the solution of a time-dependent impurity model which explicitly incorporates the probe pulse. It avoids the need to compute four-point correlation functions and can in principle be combined with different impurity solvers. This opens a path to study time-resolved RIXS processes in multiorbital systems. The approach is exemplified with a study of the RIXS signal of a melting Mott antiferromagnet.
CRIS-Team Scopus Importer:2021-04-16

Single-Molecule Junctions with Epitaxial Graphene Nanoelectrodes - Ullmann, Konrad; Brana Coto, Pedro; Leitherer, Susanne; Molina-Ontoria, Agustin; Martin, Nazario; Thoss, Michael; Weber, Heiko B. (Nano Letters, 2015)
On the way to ultraflat single-molecule junctions with transparent electrodes, we present a fabrication scheme based on epitaxial graphene nanoelectrodes. As a suitable molecule, we identified a molecular wire with fullerene anchor groups. With these two components, stable electrical characteristics could be recorded, Electrical measurements show that single-molecule junctions with graphene and with gold electrodes display a striking agreement. This motivated a hypothesis that the differential Conductance spectra are rather insensitive to the electrode material. It is further corroborated by the assignment of asymmetries and spectral features to internal molecular,degrees of freedom. The demonstrated open access graphene electrodes and the electrode-insensitive, molecules provide a model system that will allow for a thorough investigation of an individual single,molecule contact with additional probes.
Keywords: Epitaxial graphene nanoelectrodes; electroburning; single-molecule junctions; fullerene end groups; switching

Single-particle versus pair condensation of hard-core bosons with correlated hopping - Schmidt, Kai Phillip; et al. (Physical Review B, 2006)
We investigate the consequences of correlated hopping on the ground state properties of hard-core bosons on a square lattice as revealed by extensive exact diagonalizations and quantum Monte Carlo simulations. While for noninteracting hard-core bosons the effective attraction induced by the correlated hopping leads to phase separation at low density, we show that a modest nearest-neighbor repulsion suppresses phase separation, leading to a remarkable low-density pairing phase with no single particle Bose-Einstein condensation but long-range two-particle correlations, signaling a condensation of pairs. We also explain why the unusual properties of the pairing phase are a real challenge for standard one-worm quantum Monte Carlo simulations.

Single shot i-Toffoli gate in dispersively coupled superconducting qubits - Baker, Aneirin J.; Huber, Gerhard B. P.; Glaser, Niklas J.; Roy, Federico; Tsitsilin, Ivan; Filipp, Stefan; Hartmann, Michael (Applied Physics Letters, 2022)
Quantum algorithms often benefit from the ability to execute multi-qubit (> 2) gates. To date, such multi-qubit gates are typically decomposed into single- and two-qubit gates, particularly in superconducting qubit architectures. The ability to perform multi-qubit operations in a single step could vastly improve the fidelity and execution time of many algorithms. Here, we propose a single shot method for executing an i-Toffoli gate, a three-qubit gate with two control and one target qubit, using currently existing superconducting hardware. We show numerical evidence for a process fidelity over 99.5% and a gate time of 450 ns for superconducting qubits interacting via tunable couplers. Our method can straight forwardly be extended to implement gates with more than two control qubits at similar fidelities.
CRIS-Team WoS Importer:2022-03-18

Singlet fission in pentacene dimers - Zirzlmeier, Johannes; Lehnherr, Dan; Brana Coto, Pedro; Chernick, Erin; Casillas, Ruben; Basel, Bettina; Thoss, Michael; Tykwinski, Rik; Guldi, Dirk Michael (Proceedings of the National Academy of Sciences of the United States of America, 2015)
Singlet fission (SF) has the potential to supersede the traditional solar energy conversion scheme by means of boosting the photon-to-current conversion efficiencies beyond the 30% Shockley-Queisser limit. Here, we show unambiguous and compelling evidence for unprecedented intramolecular SF within regioisomeric pentacene dimers in room-temperature solutions, with observed triplet quantum yields reaching as high as 156 ± 5%. Whereas previous studies have shown that the collision of a photoexcited chromophore with a ground-state chromophore can give rise to SF, here we demonstrate that the proximity and sufficient coupling through bond or space in pentacene dimers is enough to induce intramolecular SF where two triplets are generated on one molecule.

Six-Color Confocal Immunofluorescence Microscopy with 4-Laser Lines - Heger, Lukas; Lühr, Jennifer J.; Amon, Lukas; Smith, Ana-Suncana; Eissing, Nathalie; Dudziak, Diana (Methods in Molecular Biology, 2021)
Confocal immunofluorescence microscopy is an advanced imaging technique routinely applied in the laboratory and clinics. Histological analyses are performed from tissue material. In general, a single fluorochrome per laser is employed, limiting simultaneous analysis to four antigens in one staining with a conventional 4-laser line microscope. Here, we describe a protocol for combining fluorochromes with the same excitation but different emission properties that allows for the analysis of six different antigens in confocal immunofluorescence microscopy with a conventional 4-laser line microscope. The proposed multiplexed method permits the identification and characterization of complex cell populations in rare tissue material.
CRIS-Team Scopus Importer:2021-10-01
Keywords: DC; Dendritic cells; Fluorochrome; Histology; Multicolor imaging; Tissue

SL(2,C) Chern-Simons theory, flat connections, and four-dimensional quantum geometry - Haggard, Hal M.; Han, Muxin; Kaminski, Wojciech; Riello, Aldo (Advances in Theoretical and Mathematical Physics, 2019)
A correspondence between three-dimensional flat connections and constant curvature four-dimensional simplices is used to give a novel quantization of geometry via complex SL(2, C) Chern-Simons theory. The resulting quantum geometrical states are hence represented by the 3d blocks of analytically continued Chern-Simons theory. In the semiclassical limit of this quantization the three-dimensional Chern-Simons action, remarkably, becomes the discrete Einstein-Hilbert action of a 4-simplex, featuring the appropriate boundary terms as well as the essential cosmological term proportional to the simplex's curved 4-volume. Both signs of the curvature and associated cosmological constant are present in the class of flat connections that give rise to this correspondence. We provide a Wilson graph operator that picks out this class of connections. We discuss how to promote these results to a model of Lorentzian covariant quantum gravity encompassing both signs of the cosmological constant. This paper presents the details for the results reported in [1].
CRIS-Team WoS Importer:2020-01-31

SL(2,R) model with two Hamiltonian constraints - Montesinos, Merced; Rovelli, Carlo; Thiemann, Thomas (Physical Review D, 1999)
We describe a simple dynamical model characterized by the presence of two noncommuting Hamiltonian constraints. This feature mimics the constraint structure of general relativity, where there is one Hamiltonian constraint associated with each space point. We solve the classical and quantum dynamics of the model, which turns out to be governed by an SL(2,R) gauge symmetry, local in time. In classical theory, we solve the equations of motion, find an SO(2,2) algebra of Dirac observables, find the gauge transformations for the Lagrangian and canonical variables and for the Lagrange multipliers. In quantum theory, we find the physical states, the quantum observables, and the physical inner product, which is determined by the reality conditions. In addition, we construct the classical and quantum evolving constants of the system. The model illustrates how to describe physical gauge-invariant relative evolution when coordinate time evolution is a gauge. [S0556-2821(99)02014-7].

Sokratische Dialoge. Raoul Schrott im Dialog zu «Tropen« und »Gehirn und Gedicht« - Heydenreich, Aura; Mecke, Klaus (Physik und Poetik. Produktionsästhetik und Werkgenese. Autorinnen und Autoren im Dialog, 2015)

Solids and Supersolids of Three-Body Interacting Polar Molecules on an Optical Lattice - Schmidt, Kai Phillip; Dorier, Julien; Laeuchli, Andreas M. (Physical Review Letters, 2008)
We study the physics of cold polar molecules loaded into an optical lattice in the regime of strong three-body interactions, as put forward recently by Buchler et al. [Nature Phys. 3, 726 (2007)]. To this end, quantum Monte Carlo simulations, exact diagonalization, and a semiclassical approach are used to explore hard-core bosons on the 2D square lattice which interact solely by long-ranged three-body terms. The resulting phase diagram shows a sequence of solid and supersolid phases. Our findings are directly relevant for future experimental implementations and open a new route towards the discovery of a lattice supersolid phase in experiment.

Solution-based intramolecular singlet fission in cross-conjugated pentacene dimers - Zirzlmeier, Johannes; Casillas, Ruben; Reddy, Rajagopala; Coto, Pedro B.; Lehnherr, Dan; Chernick, Erin; Papadopoulos, Ilias; Thoss, Michael; Tykwinski, Rik; Guldi, Dirk Michael (Nanoscale, 2016)
We show unambiguous and compelling evidence by means of pump-probe experiments, which are complemented by calculations using ab initio multireference perturbation theory, for intramolecular singlet fission (SF) within two synthetically tailored pentacene dimers with cross-conjugation, namely XC1 and XC2. The two pentacene dimers differ in terms of electronic interactions as evidenced by perturbation of the ground state absorption spectra stemming from stronger through-bond contributions in XC1 as confirmed by theory. Multiwavelength analysis, on one hand, and global analysis, on the other hand, confirm that the rapid singlet excited state decay and triplet excited state growth relate to SF. SF rate constants and quantum yields increase with solvent polarity. For example, XC2 reveals triplet quantum yields and rate constants as high as 162 ± 10% and (0.7 ± 0.1) × 1012 s-1, respectively, in room temperature solutions.
EAM Import::2019-03-13

Solvation of proteins: Linking thermodynamics to geometry - Mecke, Klaus; et al. (Physical Review Letters, 2007)
We calculate the solvation free energy of proteins in the tube model of Banavar and Maritan [Rev. Mod. Phys. 75, 23 (2003)] using morphological thermodynamics which is based on Hadwiger's theorem of integral geometry. Thereby we extend recent results by Snir and Kamien [Science 307, 1067 (2005)] to hard-sphere solvents at finite packing fractions and obtain new conclusions. Depending on the solvent properties, parameter regions are identified where the beta sheet, the optimal helix, or neither is favored.

Some results concerning the representation theory of the algebra underlying loop quantum gravity - Sahlmann, Hanno (Journal of Mathematical Physics, 2011)
Important characteristics of the loop approach to quantum gravity are a specific choice of the algebra A of (kinematical) observables and of a representation of A on a measure space over the space of generalized connections. This representation is singled out by its elegance and diffeomorphism covariance. Recently, in the context of the quest for semiclassical states, states of the theory in which the quantum gravitational field is close to some classical geometry, it was realized that it might also be worthwhile to study different representations of the algebra A. The content of the present work is the observation that under some mild assumptions, the mathematical structure of representations of A can be analyzed rather effortlessly, to a certain extent: each representation can be labeled by sets of functions and measures on the space of (generalized) connections that fulfill certain conditions. © 2011 American Institute of Physics.

Source polarisation independent single-shot cross-polarised optical coherence tomography approaches: a comparison - Blessing, Katharina; Schirmer, Judith; Sharma, Gargi; Singh, Kanwarpal (Optics InfoBase Conference Papers, 2022)
We have developed several methods to realise a cross-polarised optical coherence tomography system that works independent of the polarisation state of the source. Here, we compare the performance of these approaches.
CRIS-Team Scopus Importer:2022-10-21

Spectral properties of magnetic excitations in cuprate two-leg ladder systems - Schmidt, Kai Phillip; Uhrig, G. S. (2005)
This article summarizes and extends the recent developments in the microscopic modeling of the magnetic excitations in cuprate two-leg ladder systems. The microscopic Hamiltonian comprises dominant Heisenberg exchange terms plus an additional four-spin interaction which is about five times smaller. We give an over-view over the relevant energies like the one-triplon dispersion, the energies of two-triplon bound states and the positions of multi-triplon continua and over relevant spectral properties like spectral weights and spectral densities in the parameter regime appropriate for cuprate systems. It is concluded that an almost complete understanding of the magnetic excitations in undoped cuprate ladders has been obtained as measured by inelastic neutron scattering, inelastic light (Raman) scattering and infrared absorption.
Keywords: magnetic excitations; spin ladders; spin liquids; four-spin ring exchange; high-T-c superconductivity; spectral densities; continuous unitary transformations

Spectral properties of the dimerized and frustrated S=1/2 chain - Schmidt, Kai Phillip; et al. (Physical Review B, 2004)
Spectral densities are calculated for the dimerized and frustrated S=1/2 chain using the method of continuous unitary transformations. The transformation to an effective triplon model is realized in a perturbative fashion up to high orders about the limit of isolated dimers. An efficient description in terms of triplons (elementary triplets) is possible: a detailed analysis of the spectral densities is provided for strong and intermediate dimerization including the influence of frustration. Precise predictions are made for inelastic neutron scattering experiments probing the S=1 sector and for optical experiments (Raman scattering, infrared absorption) probing the S=0 sector. Bound states and resonances influence the important continua strongly. The comparison with the field theoretic results reveals that the sine-Gordon model describes the low-energy features for strong to intermediate dimerization only at critical frustration.

Spectral Properties of Unimodular Lattice Triangulations - Krüger, Benedikt; Schmidt, Ella; Mecke, Klaus (Journal of Statistical Physics, 2016)
Random unimodular lattice triangulations have been recently used as an embedded random graph model, which exhibit a crossover behavior between an ordered, large-world and a disordered, small-world behavior. Using the ergodic Pachner flips that transform such triangulations into another and an energy functional that corresponds to the degree distribution variance, Markov chain Monte Carlo simulations can be applied to study these graphs. Here, we consider the spectra of the adjacency and the Laplacian matrix as well as the algebraic connectivity and the spectral radius. Power law dependencies on the system size can clearly be identified and compared to analytical solutions for periodic ground states. For random triangulations we find a qualitative agreement of the spectral properties with well-known random graph models. In the microcanonical ensemble analytical approximations agree with numerical simulations. In the canonical ensemble a crossover behavior can be found for the algebraic connectivity and the spectral radius, thus combining large-world and small-world behavior in one model. The considered spectral properties can be applied to transport problems on triangulation graphs and the crossover behavior allows a tuning of important transport quantities.
Keywords: Triangulations; Random graphs; Networks; Spectral graph theory

Spectroscopy of a topological phase - Kamfor, Michael; Dusuel, Sebastien; Vidal, Julien; Schmidt, Kai Phillip (Physical Review B, 2014)
Dynamical correlation functions of the toric code in a uniform magnetic field are studied inside the topological phase, in the small-field limit. Such an experimentally measurable quantity displays rich field-dependent features that can be understood via the interplay of the kinetics and the interaction of the anyonic excitations. In particular, it is sensitive to the two-quasiparticle bound states that are present in the spectrum for a wide range of magnetic fields. Interestingly, such collective modes can even constitute the lowest-energy excitations of the system.

SPHERICALLY SYMMETRICAL GRAVITY AS A COMPLETELY INTEGRABLE SYSTEM - Kastrup, Hans; Thiemann, Thomas (Nuclear Physics B, 1994)
It is shown - in Ashtekar's canonical framework of General Relativity - that spherically symmetric (Schwarzschild) gravity in four-dimensional space-time constitutes a finite-dimensional completely integrable system. Canonically conjugate observables for asymptotically flat spacetimes are masses as action variables and - surprisingly - time variables as angle variables, each of which is associated with an asymptotic ''end'' of the Cauchy surfaces. The emergence of the time observable is a consequence of the Hamiltonian formulation and its subtleties concerning the slicing of space and time and is not in contradiction to Birkhoff's theorem. The results are of interest as to the concept of time in General Relativity, They can be formulated within the ADM formalism, too. Quantization of the system and the associated Schrodinger equation depend on the allowed spectrum of the masses.

Spherically symmetric gravity and the notion of time in General Relativity - Kastrup, Hans; Thiemann, Thomas (1995)

Spherical symmetric gravitational collapse of a dust cloud: Polymerized dynamics in reduced phase space - Giesel, Kristina; Han, Muxin; Li, Bao Fei; Liu, Hongguang; Singh, Parampreet (Physical Review D, 2023)
Based on the effective dynamics in the μ¯ scheme of the spherical symmetry reduced model in the reduced phase space formulation of loop quantum gravity (LQG), we investigate the gravitational collapse of a homogeneous dust cloud, with Gaussian dust serving as both the reference field and the source of the gravitational collapse. The effective dynamics from the considered model for a homogeneous dust cloud reduces precisely to the effective dynamics of loop quantum cosmology (LQC) with extrinsic curvature based K-quantization, indicating that the LQC effective dynamics lives as a subsector of the model presented here. In both the marginally bound and the bound cases of the collapse in effective dynamics, the singularity is resolved and replaced by a bounce. Though quantum geometric modification from spatial curvature is not directly included in the K-quantization it does affect the qualitative dynamics of the collapsing dust cloud in the sense that on the one hand for the marginally bound case, the dust cloud bounces once at fixed maximum energy density and on the other hand for the bound case, the dust cloud undergoes infinite cycles of contraction and expansion at energy densities dependent on the dust mass. Finally, the mass threshold for the formation of a trapped surface in each case is found and the matching conditions between the interior collapsing spacetime and an effective exterior static solution are discussed.
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Spin cat states in ferromagnetic insulators - Sharma, Sanchar; Bittencourt, Victor A.S.V.; Karenowska, Alexy D.; Viola Kusminskiy, Silvia (Physical Review B, 2021)
Generating nonclassical states in macroscopic systems is a long-standing challenge. A promising platform in the context of this quest are novel hybrid systems based on magnetic dielectrics, where photons can couple strongly and coherently to magnetic excitations, although a nonclassical state therein is yet to be observed. We propose a scheme to generate a magnetization cat state, i.e., a quantum superposition of two distinct magnetization directions, using a conventional setup of a macroscopic ferromagnet in a microwave cavity. Our scheme uses the ground state of an ellipsoid shaped magnet, which displays anisotropic quantum fluctuations akin to a squeezed vacuum. The magnetization collapses to a cat state by either a single photon or a parity measurement of the microwave cavity state. We find that a cat state with two components separated by ∼5ℏ is feasible and briefly discuss potential experimental setups that can achieve it.
CRIS-Team Scopus Importer:2021-04-02

Spin-foam model for gravity coupled to massless scalar field - Kisielowski, Marcin; Lewandowski, Jerzy (Classical and Quantum Gravity, 2019)
A spin-foam model is derived from the canonical model of loop quantum gravity coupled to a massless scalar field. We generalized to the full theory the scheme first proposed in the context of loop quantum cosmology by Ashtekar et al (2009 Phys. Len. B 681 347-52), later developed by Henderson et al (2011 Glass. Quantum Grav. 28 025003).
CRIS-Team WoS Importer:2019-03-22

Spinfoam on a Lefschetz thimble: Markov chain Monte Carlo computation of a Lorentzian spinfoam propagator - Han, Muxin; Huang, Zichang; Liu, Hongguang; Qu, Dongxue; Wan, Yidun (Physical Review D, 2021)
We compute numerically the Lorentzian Engle-Pereira-Rovelli-Livine spinfoam propagator on a 4-simplex, by adapting the Lefschetz thimble and Markov chain Monte-Carlo methods to oscillatory spinfoam integrals. Our method can compute any spinfoam observables at relatively large spins. We obtain the numerical results of the propagators at different spins and demonstrate their consistency with the expected spinfoam semiclassical behavior in the large spin limit. Our results exhibit significant quantum corrections at smaller spins. Our method is reliable and thus can be employed to discover the semiclassical and quantum behaviors of the spinfoam model.
CRIS-Team Scopus Importer:2021-05-07

Spin liquid and quantum phase transition without symmetry breaking in a frustrated three-dimensional Ising model - Roechner, Julia; Balents, Leon; Schmidt, Kai Phillip (Physical Review B, 2016)
We show that the highly frustrated transverse-field Ising model on the three-dimensional pyrochlore lattice realizes a first-order phase transition without symmetry breaking between the low-field Coulomb quantum spin liquid and the high-field polarized phase. The quantum phase transition is located quantitatively by comparing low-and high-field series expansions. Furthermore, the intriguing properties of the elementary excitations in the polarized phase are investigated. We argue that this model can be achieved experimentally by applying mechanical strain to a classical spin-ice material composed of non-Kramers spins such as Ho2Ti2O7. Taken together with our results, this provides an experimental platform to study quantum spin liquid physics.

Spinodal dewetting in liquid crystal and liquid metal films - Mecke, Klaus; et al. (Science, 1998)
Theory predicts that dewetting of a homogeneous liquid film from a solid surface may proceed via unstable surface waves on the Liquid. This phenomenon, usually termed spinodal dewetting, has been sought after in many systems. Observations in liquid crystal and Liquid metal films showed that, as expected, the emerging structures were similar to those found for spinodal decomposition in mixtures. Certain differences, however, could be attributed to peculiarities of the wetting forces in these two dissimilar systems, thereby demonstrating the role of nonlinearities inherent in the wetting forces.

Splitting of the Universality Class of Anomalous Transport in Crowded Media - Spanner, Markus; Hoefling, Felix; Kapfer, Sebastian; Mecke, Klaus; Schroeder-Turk, Gerd E.; Franosch, Thomas (Physical Review Letters, 2016)
We investigate the emergence of subdiffusive transport by obstruction in continuum models for molecular crowding. While the underlying percolation transition for the accessible space displays universal behavior, the dynamic properties depend in a subtle nonuniversal way on the transport through narrow channels. At the same time, the different universality classes are robust with respect to introducing correlations in the obstacle matrix as we demonstrate for quenched hard-sphere liquids as underlying structures. Our results confirm that the microscopic dynamics can dominate the relaxational behavior even at long times, in striking contrast to glassy dynamics.

Stability of particles in two-dimensional quasicrystals against phasonic perturbations - Martinsons, Miriam; Schmiedeberg, Michael (Journal of Physics: Conference Series, 2020)
We investigate particles in two-dimensional quasicrystalline interference patterns and present a method to determine for each particle at which phasonic displacement a phasonic flip occurs. By mapping all particles into characteristic areas of reduced phononic and phasonic displacements, we identify the particles that are close to edges of these areas and can easily flip. In contrast, the particles in the center are hardly affected by phasonic fluctuations. Our results are important e.g. for light-induced colloidal structures or cold atomic gases in laser traps. In addition, our approach can help to predict how thermal fluctuations induce phasonic flips in intrinsic quasicrystals with structures close to interference pattern
Keywords: quasicrystals; phasons

Stabilization of Multimode Schrodinger Cat States Via Normal-Mode Dissipation Engineering - Zapletal, Petr; Nunnenkamp, Andreas; Brunelli, Matteo (PRX Quantum, 2022)
Non-Gaussian quantum states have been deterministically prepared and autonomously stabilized in single- and two-mode circuit quantum electrodynamics architectures via engineered dissipation. However, it is currently unknown how to scale up this technique to multimode non-Gaussian systems. Here, we upgrade dissipation engineering to collective (normal) modes of nonlinear resonator arrays and show how to stabilize multimode Schrodinger cat states. These states are multiphoton and multimode quantum superpositions of coherent states in a single normal mode delocalized over an arbitrary number of cavities. We consider tailored dissipative coupling between resonators that are parametrically driven and feature an on-site nonlinearity, which is either a Kerr-type nonlinearity or an engineered two-photon loss. For both types of nonlinearity, we find the same exact closed-form solutions for the two-dimensional steady-state manifold spanned by superpositions of multimode Schrodinger cat states. We further show that, in the Zeno limit of strong dissipative coupling, the even-parity multimode cat state can be deterministically prepared from the vacuum. Remarkably, engineered two-photon loss gives rise to a fast relaxation toward the steady state, protecting the state preparation against decoherence due to intrinsic single-photon losses and imperfections in tailored dissipative coupling, which sets in at longer times. The relaxation time is independent of system size making the state preparation scalable. Multimode cat states are naturally endowed with a noise bias that increases exponentially with system size and can thus be exploited for enhanced robust encoding of quantum information.
CRIS-Team WoS Importer:2022-01-21

Stabilizing quasicrystals composed of patchy colloids by narrowing the patch width - Gemeinhardt, Anja; Martinsons, Miriam; Schmiedeberg, Michael (EPL - Europhysics Letters, 2019)
We explore the behavior of two-dimensional patchy colloidal particles with 8 or 10 symmetrically arranged patches by employing Monte Carlo simulations. The particles interact according to an isotropic pair potential that possesses only one typical length. The patches lead to additional attractions that are anisotropic and depend on the relative orientation of two neighboring particles. We investigate the assembled structures with a special interest in quasicrystals. We found that the patch width is of great importance: Only in the case of narrow patch widths we are able to observe metastable octagonal and decagonal quasicrystals, while dodecagonal quasicrystals can also occur for broad patches. These results are important to understand the role of interactions with preferred binding angles in order to obtain quasicrystals. Our findings suggest that in the case of sharp binding angles, as they occur in metallic alloys, octagonal and decagonal symmetries might be observed more often than in systems with less sharp binding angles as it is the case in soft-matter systems where dodecagonal quasicrystals dominate.

Stable coherent states - Zipfel, Antonia; Thiemann, Thomas (Physical Review D, 2016)
We analyze the stability under time evolution of complexitier coherent states (CCS) in one-dimensional mechanical systems. A system of coherent states is called stable if it evolves into another coherent state. It turns out that a system can only possess stable CCS if the classical evolution of thc variable z = e-14(i xc)q pound for a given complexifier C depends only on z itself and not on its complex conjugate. This condition is very restrictive in general so that only a few systems exist that obey this condition. However, it is possible to access a wider class of models that in principle may allow for stable coherent states associated with certain regions in the phase space by introducing action-angle coordinates.

State-dependent Trotter limits and their approximations - Burgarth, Daniel; Galke, Niklas; Hahn, Alexander; Van Luijk, Lauritz (Physical Review A, 2023)
The Trotter product formula is a key instrument in numerical simulations of quantum systems. However, computers cannot deal with continuous degrees of freedom, such as the position of particles in molecules, or the amplitude of electromagnetic fields. It is therefore necessary to discretize these variables to make them amenable to digital simulations. Here, we give sufficient conditions to conclude the validity of this approximate discretized physics. Essentially, it depends on the state-dependent Trotter error, for which we establish explicit bounds that are also of independent interest.
CRIS-Team Scopus Importer:2023-04-28

Statistical Mechanics of an Elastically Pinned Membrane: Equilibrium Dynamics and Power Spectrum - Janeš, Josip Augustin; Schmidt, Daniel; Blackwell, Robert; Seifert, Udo; Smith, Ana-Suncana (Biophysical Journal, 2019)
In biological settings, membranes typically interact locally with other membranes: the extracellular matrix in the exterior or internal cellular structures such as the cytoskeleton, locally pinning the membrane. Characterizing the dynamical properties of such interactions presents a difficult task. Significant progress has been achieved through simulations and experiments, yet analytical progress in modeling pinned membranes has been impeded by the complexity of governing equations. Here, we circumvent these difficulties by calculating analytically the time-dependent Green's function of the operator governing the dynamics of an elastically pinned membrane in a hydrodynamic surrounding and subject to external forces. This enables us to calculate the equilibrium power spectral density for an overdamped membrane pinned by an elastic, permanently attached spring subject to thermal excitations. By considering the effects of the finite experimental resolution on the measured spectra, we show that the elasticity of the pinning can be extracted from the experimentally measured spectrum. Membrane fluctuations can thus be used as a tool to probe mechanical properties of the underlying structures. Such a tool may be particularly relevant in the context of cell mechanics, in which the elasticity of the membrane's attachment to the cytoskeleton could be measured.
CRIS-Team Scopus Importer:2019-08-06

Statistical Mechanics of an Elastically Pinned Membrane: Static Profile and Correlations - Janeš, Josip Augustin; Stumpf, Henning; Schmidt, Daniel; Seifert, Udo; Smith, Ana-Suncana (Biophysical Journal, 2019)
The relation between thermal fluctuations and the mechanical response of a free membrane has been explored in great detail, both theoretically and experimentally. However, understanding this relationship for membranes locally pinned by proteins is significantly more challenging. Given that the coupling of the membrane to the cell cytoskeleton, to the extracellular matrix, and to other internal structures is crucial for the regulation of a number of cellular processes, understanding the role of the pinning is of great interest. In this manuscript, we consider a single protein (elastic spring of a finite rest length) pinning a membrane modeled in the Monge gauge. First, we determine the Green's function for the system and complement this approach by the calculation of the mode-coupling coefficients for the plane wave expansion and the orthonormal fluctuation modes, in turn building a set of tools for numerical and analytic studies of a pinned membrane. Furthermore, we explore static correlations of the free and the pinned membrane, as well as the membrane shape, showing that all three are mutually interdependent and have an identical long-range behavior characterized by the correlation length. Interestingly, the latter displays a nonmonotonic behavior as a function of membrane tension. Importantly, exploiting these relations allows for the experimental determination of the elastic parameters of the pinning. Last but not least, we calculate the interaction potential between two pinning sites and show that even in the absence of the membrane deformation, the pinnings will be subject to an attractive force because of changes in membrane fluctuations.
CRIS-Team Scopus Importer:2019-06-07

STATISTICAL MORPHOLOGY OF RANDOM INTERFACES IN MICROEMULSIONS - Mecke, Klaus; et al. (Journal of Chemical Physics, 1995)

Stochastic dynamics of substrate non-uniform stiffness affecting molecular adhesion in cell-substrate interface subjected to tensile loading - Qi, Chenwei; Zhang, Juanjuan; Smith, Ana-Suncana; Li, Long (Journal of Applied Physics, 2023)
The mechanically heterogeneous extracellular matrix (ECM) or tissues widely exist in biological systems and are capable of significantly regulating directional cell migration. However, prior to whole cell movement, how the cell senses these cues from mechanical heterogeneities of the ECM or substrate remains unclear at the molecular bond level. To address this issue, we theoretically investigate interface adhesion between a non-uniform stiffness substrate and a rigid plate via a series of receptor-ligand bonds subjected to a tensile loading by integrating substrate surface deformation described by continuum mechanics approach into the stochastic events of bond dissociation and association govern by Markov processes. Interestingly, it is found that, during stretching adhesion interface, due to the large collective contact forces near the stiff edge of the adhesion area, the crack first develops at this stiff edge and then grows to another relatively soft adhesion edge until the completed detachment achieved, which is distinct from the cracks growing from both two edges to center of adhesion area in the case of uniformly elastic solid-solid or solid-fluid interface. Moreover, the lifetime of the bond cluster, interface adhesion strength, and the effect of inter-bond distance are examined, respectively. The corresponding mechanism of dependence of the lifetime and adhesion strength on the non-uniform stiffness of the substrate and inter-bond distance is also analyzed. These findings provide a detailed mechanistic understanding of the adhesion interface responding to the mechanical heterogeneities of the substrate at the molecular bond level.
CRIS-Team Scopus Importer:2023-07-07

Stochastic semiclassical theory for nonequilibrium electron-phonon coupled systems - Picano, Antonio; Grandi, Francesco; Werner, Philipp; Eckstein, Martin (Physical Review B, 2023)
We discuss a semiclassical approach to solve the quantum impurity model within nonequilibrium dynamical mean-field theory for electron-lattice models. The effect of electronic fluctuations on the phonon is kept beyond Ehrenfest dynamics, leading to a stochastic phonon evolution with damping and noise terms that are self-consistently determined by the electronic correlation functions in the fluctuating phonon field. Together with a solution of the electronic model based on a nonperturbative quantum Boltzmann equation, the approach can be used to address the coupled dynamics of the electrons and the lattice during photoinduced phase transitions. Results for the Anderson-Holstein model are benchmarked against numerically exact quantum Monte Carlo data. We find good agreement for the phonon distribution function at temperatures comparable to the charge ordering temperature. The general formulation can be extended to models with electron-electron interactions or multiorbital systems.
CRIS-Team Scopus Importer:2023-08-04

Straintronics beyond homogeneous deformation - Gupta, Reena; Rost, Fabian; Fleischmann, Maximilian; Sharma, S.; Shallcross, Sam (Physical Review B, 2019)
We present a continuum theory of graphene, treating on an equal footing both the homogeneous Cauchy-Born (CB) deformation and the microscopic degrees of freedom associated with the two sublattices. While our theory recovers all extant results from homogeneous continuum theory, the Dirac-Weyl equation is found to be augmented by new pseudogauge and chiral fields fundamentally different from those that result from homogeneous deformation. We elucidate three striking electronic consequences: (i) non-CB deformations allow for the transport of valley-polarized charge over arbitrarily long distances, e.g., along a designed ridge; (ii) the triaxial deformations required to generate an approximately uniform magnetic field are unnecessary with non-CB deformation; and finally (iii) the vanishing of the effects of a one-dimensional corrugation seen in ab initio calculation upon lattice relaxation is explained as a compensation of CB and non-CB deformation.
CRIS-Team WoS Importer:2021-10-18

Strong dependence of percolation thresholds on polydispersity - Mecke, Klaus; et al. (EPL - Europhysics Letters, 2002)
Monte Carlo simulations for a large family of discretized Boolean models exhibit complex dependencies of the percolation threshold not only on shape and correlations but also on the polydispersity of the constituents (pores). A pronounced peak of the critical volume fraction as a function of the density fraction is found for large-size ratios of the pores. Such an increase of more than 10% even for small changes in composition of less than 1% is important in material science, where the accurate prediction of percolation thresholds for arbitrary shaped pores plays a fundamental role. A topological percolation criterion works well for dependence on shape and correlation. But none of the known explicit estimates for percolation thresholds is in reasonable quantitative agreement with the numerical data for polydisperse systems presented here.

Structural and dynamical properties of dilute gel networks in colloid–polymer mixtures - Gimperlein, Matthias; Schmiedeberg, Michael (Journal of Chemical Physics, 2021)
The competition of short-ranged depletion attraction and long-ranged repulsion between colloidal particles in colloid–polymer mixtures leads to the formation of heterogeneous gel-like structures. Our special focus will be on the states where the colloids arrange in thin strands that span the whole system and that we will refer to as dilute gel networks. These states occur at low packing fractions for attractions that are stronger than those at both the binodal line of the equilibrium gas–liquid phase separation and the directed percolation transition line. By using Brownian dynamics simulations, we explore the formation, structure, and aging dynamics of dilute gel networks. The essential connections in a dilute gel network are determined by constructing reduced networks. We compare the observed properties to those of clumpy gels or cluster fluids. Our results demonstrate that both the structure and the (often slow) dynamics of the stable or meta-stable heterogeneous states in colloid–polymer mixtures possess distinct features on various length and time scales and thus are richly divers
Keywords: colloidal gel; colloid-polymer mixture; gel network

Structural basis for the shielding function of the dynamic trypanosome variant surface glycoprotein coat - Bartossek, Thomas; Jones, Nicola G.; Schafer, Christin; Cvitkovic, Mislav; Glogger, Marius; Mott, Helen R.; Kuper, Jochen; Brennich, Martha; Carrington, Mark; Smith, Ana-Suncana; Fenz, Susanne; Kisker, Caroline; et al. (Nature Microbiology, 2017)
The most prominent defence of the unicellular parasite Trypanosoma brucei against the host immune system is a dense coat that comprises a variant surface glycoprotein (VSG). Despite the importance of the VSG family, no complete structure of a VSG has been reported. Making use of high-resolution structures of individual VSG domains, we employed small-angle X-ray scattering to elucidate the first two complete VSG structures. The resulting models imply that the linker regions confer great flexibility between domains, which suggests that VSGs can adopt two main conformations to respond to obstacles and changes of protein density, while maintaining a protective barrier at all times. Single-molecule diffusion measurements of VSG in supported lipid bilayers substantiate this possibility, as two freely diffusing populations could be detected. This translates into a highly flexible overall topology of the surface VSG coat, which displays both lateral movement in the plane of the membrane and variation in the overall thickness of the coat.
Keywords: membrane biophysics; membrane trafficking; parasite immune evasion; SAXS

Structural characterization of an ionic liquid in bulk and in nano-confined environment using data from MD simulations - Vučemilović-Alagić, Nataša; Banhatti, Radha D.; Stepic, Robert; Wick, Christian; Berger, Daniel; Gaimann, Mario U.; Baer, Andreas; Harting, Jens; Smith, David M.; Smith, Ana-Suncana (Data in Brief, 2020)
This article contains data on structural characterization of the [C2Mim][NTf2] in bulk and in nano-confined environment obtained using MD simulations. These data supplement those presented in the paper “Insights from Molecular Dynamics Simulations on Structural Organization and Diffusive Dynamics of an Ionic Liquid at Solid and Vacuum Interfaces” [1], where force fields with three different charge methods and three charge scaling factors were used for the analysis of the IL in the bulk, at the interface with the vacuum and the IL film in the contact with a hydroxylated alumina surface. Here, we present details on the construction of the model systems in an extended detailed methods section. Furthermore, for best parametrization, structural and dynamic properties of IL in different environment are studied with certain features presented herein.
CRIS-Team Scopus Importer:2019-12-10
Keywords: Interface-normal number density; Ionic liquid; Molecular dynamics simulations; Nanoconfinement; Radial distributions

Structural quantities of quasi-two-dimensional fluids - Lang, Simon; Franosch, Thomas; Schilling, Rolf (Journal of Chemical Physics, 2014)
Quasi-two-dimensional fluids can be generated by confining a fluid between two parallel walls with narrow separation. Such fluids exhibit an inhomogeneous structure perpendicular to the walls due to the loss of translational symmetry. Taking the transversal degrees of freedom as a perturbation to an appropriate 2D reference fluid we provide a systematic expansion of the m-particle density for arbitrary m. To leading order in the slit width this density factorizes into the densities of the transversal and lateral degrees of freedom. Explicit expressions for the next-to-leading order terms are elaborated analytically quantifying the onset of inhomogeneity. The case m = 1 yields the density profile with a curvature given by an integral over the pair-distribution function of the corresponding 2D reference fluid, which reduces to its 2D contact value in the case of pure excluded-volume interactions. Interestingly, we find that the 2D limit is subtle and requires stringent conditions on the fluid-wall interactions. We quantify the rapidity of convergence for various structural quantities to their 2D counterparts.
EAM Import::2019-03-13

Structural similarity between dry and wet sphere packings - Weis, Simon; Schröder-Turk, Gerd; Schröter, Matthias (New Journal of Physics, 2019)
The mechanical properties of granular materials change significantly in the presence of a wetting liquid which creates capillary bridges between the particles. This results e.g. in a reduced value of the volume fraction when a packing is prepared with added liquid. Here we use x-ray tomography to demonstrate that this change in mechanical properties is not accompanied by structural differences between dry and wet sphere packings when compared at the same volume fraction. We characterize the structure of the packings by the average numbers of contacts of each sphere < Z > and the shape isotropy <beta(2,0)(0)> of the Voronoi cells of the particles. Additionally, we show that the number of liquid bridges per sphere < B > is approximately equal to < Z > + 2, independent of the volume fraction of the packing. These findings will be helpful in guiding the development of both particle-based models and continuum mechanical descriptions of wet granular matter.
CRIS-Team WoS Importer:2019-04-30

Structural studies of local environments in high-symmetry quasicrystals - Mendoza Sosa, Alan Rodrigo; Kraemer, Ata; Oğuz, Erdal; Schmiedeberg, Michael (Scientific Reports, 2023)

SU(N) quantum Yang-Mills theory in two dimensions: A complete solution - Ashtekar, Abhay; Lewandowski, Jerzy; Marolf, Donald; Mourao, José Manuel; Thiemann, Thomas (Journal of Mathematical Physics, 1997)
A closed expression of the Euclidean Wilson-loop functionals is derived for pure Yang-Mills continuum theories with gauge groups SU(N) and U(1) and spacetime topologies R-1 x R-1 and R-1 x S-1. (For the U(1) theory, we also consider the S-1 x S-1 topology.) The treatment is rigorous, manifestly gauge invariant, manifestly invariant under area preserving diffeomorphisms and handles all (piecewise analytic) loops in one stroke. Equivalence between the resulting Euclidean theory and and the Hamiltonian framework is then established. Finally, an extension of the Osterwalder-Schrader axioms for gauge theories is proposed, These axioms are satisfied in the present model. (C) 1997 American Institute of Physics.

Super Cartan geometry and loop quantum supergravity - Eder, Konstantin (FAU University Press, 2022)
Superstring theory and loop quantum gravity (LQG) are promising approaches towards the formulation of a quantum theory of gravity. Superstring theory aims at unification of all fundamental forces of nature, predicting supersymmetry and even higher spacetime dimensions. LQG, on the other hand, takes a more conservative viewpoint by proposing new quantization techniques that take seriously the central principles of general relativity. The goal of this work is to relate ideas from LQG and superstring theory by combining LQG with the concept of supersymmetry. To achieve this, the mathematical apparatus for a mathematically rigorous description of the underlying geometric structures of supergravity theories, i.e., supersymmetric extensions of Einstein’s theory of gravity, will be developed. Among other things, this approach leads to a reformulation of the theory in which (part of) supersymmetry manifests itself in terms of a gauge symmetry. Using the interpretation of supergravity in terms of a super Cartan geometry, the Holst variant of the MacDowell-Mansouri action for (extended) AdS supergravity in D=4 for arbitrary values of the Barbero-Immirzi parameter - a free parameter of the theory - will be derived. Moreover, it will be demonstrated that these actions provide unique boundary terms that ensure local supersymmetry invariance at boundaries. The chiral case is special: The action is invariant under an enlarged gauge symmetry, the boundary theory is a topological super Chern-Simons theory, and a chiral connection emerges that is the natural generalization of the Ashtekar connection to the supersymmetric context. Making use of the enlarged gauge symmetry, a quantization of the theory generalizing standard tools of LQG will be proposed. These results provide a starting point for applications in the context of supersymmetric black holes and quantum cosmology. There, the enhanced gauge symmetry proves to be a promising tool which in the future may shed a lot of insights on how to relate results from these different approaches.<br
Keywords: Holst-MacDowell-Mansouri action; Loop quantum gravity; Super Cartan geometry; Supercosmology; Supergravity; Supermanifolds; boundary theory; super Chern-Simons theory

Super Cartan Geometry and the Super Ashtekar Connection - Eder, Konstantin (Annales Henri Poincaré, 2023)
This work is devoted to the geometric approach to supergravity. More precisely, we interpret N= 1 , D= 4 supergravity as a super Cartan geometry which provides a link between supergravity and Yang–Mills theory. To this end, we first review important aspects of the theory of supermanifolds and we establish a link between various different approaches. We then introduce super Cartan geometries using the concept of so-called enriched categories. This, among other things, will enable us to implement anticommutative fermionic fields. We will then also show that non-extended D= 4 supergravity naturally arises in this framework. Finally, using this gauge-theoretic interpretation as well as the chiral structure of the underlying supersymmetry algebra, we will derive graded analoga of Ashtekar’s self-dual variables and interpret them in terms of generalized super Cartan connections. This gives canonical chiral supergravity the structure of a Yang–Mills theory with gauge supergroup similar to the self-dual variables in ordinary first-order Einstein gravity. We then construct the parallel transport map corresponding to the super connection in mathematical rigorous way using again enriched categories. This provides the possibility of quantizing gravity and matter degrees of freedom in loop quantum gravity in a unified way.Kindly check and confirm inserted city and country name are correctly identified.City and country name are correct.
CRIS-Team Scopus Importer:2023-04-14

Superconducting optical response of photodoped Mott insulators - Li, Jiajun; Golez, D.; Werner, P.; Eckstein, Martin (Modern Physics Letters B, 2020)
Ultrafast laser pulses can redistribute charges in Mott insulators on extremely short time scales, leading to the fast generation of photocarriers. It has recently been demonstrated that these photocarriers can form a novel η-paired condensate at low temperatures, featuring a staggered superconducting pairing field. In this conference paper, we discuss the origin of the η-paired hidden phase and its optical response, which may be detected in a pump-probe experiment. The hidden phase may be relevant for possible light-induced superconductivity in Mott insulators.
CRIS-Team Scopus Importer:2020-07-10
Keywords: Mott insulators; photocarriers; Superconducting optical response; ultrafast laser techniques

Superconducting quantum many-body circuits for quantum simulation and computing - Wilkinson, Samuel; Hartmann, Michael (Applied Physics Letters, 2020)
Quantum simulators are attractive as a means to study many-body quantum systems that are not amenable to classical numerical treatment. A versatile framework for quantum simulation is offered by superconducting circuits. In this perspective, we discuss how superconducting circuits allow the engineering of a wide variety of interactions, which, in turn, allows the simulation of a wide variety of model Hamiltonians. In particular, we focus on strong photon-photon interactions mediated by nonlinear elements. This includes on-site, nearest-neighbor, and four-body interactions in lattice models, allowing the implementation of extended Bose-Hubbard models and the toric code. We discuss not only the present state in analog quantum simulation but also future perspectives of superconducting quantum simulation, which open up when concatenating quantum gates in emerging quantum computing platforms.
CRIS-Team WoS Importer:2020-07-03

Superdiffusion in a honeycomb billiard - Schmiedeberg, Michael; Stark, Holger (Physical Review E, 2006)
We investigate particle transport in the honeycomb billiard which consists of connected channels placed on the edges of a honeycomb structure. The spreading of particles is superdiffusive due to the existence of ballistic trajectories which we term perfect paths. Simulations give a time exponent of 1.72 for the mean-square displacement and a starlike, i.e., anisotropic, particle distribution. We present an analytical treatment based on the formalism of continuous-time random walks and explain the anisotropic distribution under the assumption that the perfect paths follow the directions of the six lattice axes. Furthermore, we derive a relation between the time exponent and the exponent of the distribution function for trajectories close to a perfect path. In billiards with randomly distributed channels, conventional diffusion is always observed in the long-time limit, although for small disorder transient superdiffusional behavior exists. Our simulation results are again supported by an analytical analysis.

Super fiber bundles, connection forms, and parallel transport - Eder, Konstantin (Journal of Mathematical Physics, 2021)
The present work provides a mathematically rigorous account on super fiber bundle theory, connection forms and their parallel transport, that ties together various approaches. We begin with a detailed introduction to super fiber bundles. We then introduce the concept of so-called relative supermanifolds as well as bundles and connections defined in these categories. Studying these objects turns out to be of utmost importance in order to, among other things, model anticommuting classical fermionic fields in mathematical physics. We then construct the parallel transport map corresponding to such connections and compare the results with those found by other means in the mathematical literature. Finally, applications of these methods to supergravity will be discussed such as the Cartan geometric formulation of Poincaré supergravity as well as the description of Killing vector fields and Killing spinors of super Riemannian manifolds arising from metric reductive super Cartan geometries.<br

Superlattice approach to doping infinite-layer nickelates - Ortiz, R. A.; Menke, Henri; Misjak, F.; Mantadakis, D. T.; Fuersich, K.; Schierle, E.; Logvenov, G.; Kaiser, U.; Keimer, B.; Hansmann, Philipp; Benckiser, E. (Physical Review B, 2021)
The recent observation of superconductivity in infinite-layer Nd1-xSrxNiO2 thin films has attracted a lot of attention, since this compound is electronically and structurally analogous to the superconducting cuprates. Due to the challenges in the phase stabilization upon chemical doping with Sr, we synthesized artificial superlattices of LaNiO3 embedded in insulating LaGaO3, and we used layer-selective topotactic reactions to reduce the nickelate layers to LaNiO2. Hole doping is achieved via interfacial oxygen atoms and tuned via the layer thickness. We used electrical transport measurements, transmission electron microscopy, and x-ray spectroscopy together with ab initio calculations to track changes in the local nickel electronic configuration upon reduction, and we found that these changes are reversible. Our experimental and theoretical data indicate that the doped holes are trapped at the interfacial quadratic pyramidal Ni sites. Calculations for electron-doped cases predict a different behavior, with evenly distributed electrons among the layers, thus opening up interesting perspectives for interfacial doping of transition-metal oxides.
CRIS-Team WoS Importer:2021-11-05

Superradiance and anomalous hyperfine splitting in inhomogeneous ensembles - Andrejic, Petar; Pálffy, Adriana (Physical Review A, 2021)
Collective effects in the interaction of light with ensembles of identical scatterers play an important role in many fields of physics. However, often the term "identical" is not accurate due to the presence of hyperfine fields which induce inhomogeneous transition shifts and splittings. Here we develop a formalism based on the Green's-function method to model the linear response of such inhomogeneous ensembles in one-dimensional waveguides. We obtain a compact formula for the collective spectrum, which exhibits deviations from the uniform frequency shift and broadening expected of two-level systems. In particular, if the coherent contribution to the collective coupling is large, the effect of inhomogeneous broadening can be suppressed, with the linewidth approaching that of the superradiant value. We apply this formalism to describe collective effects in x-ray scattering off thin-film waveguides for inhomogeneous hyperfine parameters.
CRIS-Team WoS Importer:2021-09-17

Supersolid phase induced by correlated hopping in spin-1/2 frustrated quantum magnets - Schmidt, Kai Phillip; Dorier, J.; Laeuchli, A. M.; Mila, F. (Physical Review Letters, 2008)
We show that correlated hopping of triplets, which is often the dominant source of kinetic energy in dimer-based frustrated quantum magnets, produces a remarkably strong tendency to form supersolid phases in a magnetic field. These phases are characterized by simultaneous modulation and ordering of the longitudinal and transverse magnetization, respectively. Using quantum Monte Carlo and a semiclassical approach for an effective hard-core boson model with nearest-neighbor repulsion on a square lattice, we prove, in particular, that a supersolid phase can exist even if the repulsion is not strong enough to stabilize an insulating phase at half-filling. Experimental implications for frustrated quantum antiferromagnets in a magnetic field at zero and finite temperature are discussed.

Supersolid Phases of Hardcore Bosons on the Square Lattice: Correlated Hopping, Next-Nearest Neighbor Hopping and Frustration - Mila, Frederic; Dorier, Julien; Schmidt, Kai Phillip (Progress of Theoretical Physics Supplement, 2008)
We discuss the appearance of supersolid phases for interacting hardcore bosons on the square lattice when, in addition to the standard nearest neighbor hopping and repulsion, correlated or next-nearest neighbor hopping is present. Having in mind dimer-based quantum magnets in a field described by effective bosonic models of this kind, we put special emphasis on a comparison between the different cases of relative signs of the kinetic processes, which correspond to unfrustrated or frustrated magnetic models. In the unfrustrated case, we compare Quantum Monte Carlo simulations with a mean-field (classical) approach, which is shown to give qualitatively correct results. Using this classical approach for the frustrated case, we find that, the phase diagram is generically richer than in the unfrustrated case. We also investigate in detail the differences between standard next-nearest neighbour and correlated hopping over the diagonal, with the conclusion that both cases are similar if checkerboard order is present at half-filling, while a supersolid phase can be stabilized without any adjacent solid phase only in the case of correlated hopping.

Supersymmetric minisuperspace models in self-dual loop quantum cosmology - Eder, Konstantin; Sahlmann, Hanno (Journal of High Energy Physics, 2021)
In this paper, we study a class of symmetry reduced models of N = 1 super- gravity using self-dual variables. It is based on a particular Ansatz for the gravitino field as proposed by D’Eath et al. We show that the essential part of the constraint algebra in the classical theory closes. In particular, the (graded) Poisson bracket between the left and right supersymmetry constraint reproduces the Hamiltonian constraint. For the quantum theory, we apply techniques from the manifestly supersymmetric approach to loop quantum supergravity, which yields a graded analog of the holonomy-flux algebra and a natural state space. We implement the remaining constraints in the quantum theory. For a certain subclass of these models, we show explicitly that the (graded) commutator of the supersymmetry constraints exactly reproduces the classical Poisson relations. In particular, the trace of the commutator of left and right supersymmetry constraints reproduces the Hamilton constraint operator. Finally, we consider the dynamics of the theory and compare it to a quantization using standard variables and standard minisuperspace techniques.
CRIS-Team Scopus Importer:2021-03-19
Keywords: Cosmology of Theories beyond the SM; Models of Quantum Gravity; Super-gravity Models

Surface tension of isotropic-nematic interfaces: Fundamental measure theory for hard spherocylinders - Wittmann, Rene; Mecke, Klaus (Journal of Chemical Physics, 2014)
A fluid constituted of hard spherocylinders is studied using a density functional theory for nonspherical hard particles, which can be written as a function of weighted densities. This is based on an extended deconvolution of the Mayer f-function for arbitrarily shaped convex hard bodies in tensorial weight functions, which depend each only on the shape and orientation of a single particle. In the course of an examination of the isotropic-nematic interface at coexistence the functional is applied to anisotropic and inhomogeneous problems for the first time. We find good qualitative agreement with other theoretical predictions and also with Monte Carlo simulations. (c) 2014 AIP Publishing LLC.

Surprising Charge-Radius Kink in the Sc Isotopes at N=20 - König, Kristian; Fritzsche, Stephan; Hagen, Gaute; Holt, Jason D.; Klose, Andrew; Lantis, Jeremy; Liu, Yuan; Minamisono, Kei; Miyagi, Takayuki; Nazarewicz, Witold; Papenbrock, Thomas; Pineda, Skyy V.; et al. (Physical Review Letters, 2023)
Charge radii of neutron deficient ^40Sc and ^41Sc nuclei were determined using collinear laser spectroscopy. With the new data, the chain of Sc charge radii extends below the neutron magic number N=20 and shows a pronounced kink, generally taken as a signature of a shell closure, but one notably absent in the neighboring Ca, K, and Ar isotopic chains. Theoretical models that explain the trend at N=20 for the Ca isotopes cannot reproduce this puzzling behavior.
CRIS-Team Scopus Importer:2023-10-06

Swept source cross-polarized optical coherence tomography for any input polarized light - Sharma, Gargi; Sharma, Shivani; Blessing, Katharina; Hartl, Georg; Waldner, Maximilian; Singh, Kanwarpal (Journal of Optics, 2020)
Cross polarized optical coherence tomography (OCT) offers enhanced contrast in certain pathological conditions. Traditional cross-polarized OCT systems require a defined input polarization and thus require several polarization controlling elements increasing the overall complexity of the system. Our proposed system requires a single quarter wave plate as a polarization controller thus simplifying the system significantly. The majority of cross-polarized OCT systems are spectrometer based, which suffers from slow speed and low signal to noise ratio. In this work, we present a swept source based cross-polarized OCT system that works for any input polarization state. The system was tested against known birefringent materials such as quarter wave plate. Furthermore, biological samples such as finger, nail and chicken breast were imaged to demonstrate the potential of our technique.
CRIS-Team WoS Importer:2020-04-03

Switching from Ultraweak to Strong Adhesion - Fenz, Susanne F.; Bihr, Timo; Merkel, Rudolf; Seifert, Udo; Sengupta, Kheya; Smith, Ana-Suncana (Advanced Materials, 2011)
Intrinsically strong avidin-neutravidin bonds can exhibit ultraweak adhesion mediated by transiently bound domains and can undergo a transition to a stable strong adhesion by locally increasing bond density.
Keywords: INTERFERENCE CONTRAST MICROSCOPY; CELL-ADHESION; SUPPORTED MEMBRANES; DIFFUSION; DYNAMICS; FLUCTUATIONS; MOLECULES; VESICLES; SURFACE; BONDS

Switching the conductance of a molecular junction using a proton transfer reaction - Hofmeister, Chriszandro; Härtle, Rainer; Rubio-Pons, Oscar; Brana Coto, Pedro; Sobolewski, Andrzej L.; Thoss, Michael (Journal of Molecular Modeling, 2014)
A novel mechanism for switching a molecular junction based on a proton transfer reaction triggered by an external electrostatic field is proposed. As a specific example to demonstrate the feasibility of the mechanism, the tautomers [2,5-(4-hydroxypyridine)] and 2,5-[4(1H)-pyridone] are considered. Employing a combination of first-principles electronic structure calculations and Landauer transport theory, we show that both tautomers exhibit very different conductance properties and realize the "on" and "off" states of a molecular switch. Moreover, we provide a proof of principle that both forms can be reversibly converted into each other using an external electrostatic field. © Springer-Verlag 2014.
UnivIS-Import:2015-04-14:Pub.2014.nat.dphy.ITP.ppem.switch
Keywords: Charge transport; Density functional theory; Molecular electronics; Molecular switch; Single molecule junction

Symmetric scalar constraint for loop quantum gravity - Sahlmann, Hanno; Lewandowski, Jerzy (Physical Review D - Particles, Fields, Gravitation and Cosmology, 2015)
In the framework of loop quantum gravity, we define a new Hilbert space of states which are solutions of a large number of components of the diffeomorphism constraint. On this Hilbert space, using the methods of Thiemann, we obtain a family of gravitational scalar constraints. They preserve the Hilbert space for every choice of lapse function. Thus adjointness and commutator properties of the constraint can be investigated in a straightforward manner. We show how the space of solutions of the symmetrized constraint can be defined by spectral decomposition, and the Hilbert space of physical states by subsequently fully implementing the diffeomorphism constraint. The relationship of the solutions to those resulting from a proposal for a symmetric constraint operator by Thiemann remains to be elucidated.

Symmetry detection of auxetic behaviour in 2D frameworks - Mitschke, Holger; Schröder-Turk, Gerd; Mecke, Klaus; Fowler, P. W.; Guest, S. D. (EPL - Europhysics Letters, 2013)
A symmetry-extended Maxwell treatment of the net mobility of periodic bar-and-joint frameworks is used to derive a sufficient condition for auxetic behaviour of a 2D material. The type of auxetic behaviour that can be detected by symmetry has Poisson's ratio -1, with equal expansion/contraction in all directions, and is here termed equiauxetic. A framework may have a symmetry-detectable equiauxetic mechanism if it belongs to a plane group that includes rotational axes of order n = 6, 4, or 3. If the reducible representation for the net mobility contains mechanisms that preserve full rotational symmetry (A modes), these are equiauxetic. In addition, for n = 6, mechanisms that halve rotational symmetry (B modes) are also equiauxetic. Copyright (c) EPLA, 2013

Synthetic mean-field interactions in photonic lattices - Duncan, Callum W.; Hartmann, Michael; Thomson, Robert R.; Öhberg, Patrik (European Physical Journal D, 2020)
Abstract: Photonic lattices are usually considered to be limited by their lack of methods to include interactions. We address this issue by introducing mean-field interactions through optical components which are external to the photonic lattice. The proposed technique to realise mean-field interacting photonic lattices relies on a Suzuki-Trotter decomposition of the unitary evolution for the full Hamiltonian. The technique realises the dynamics in an analogous way to that of a step-wise numerical implementation of quantum dynamics, in the spirit of digital quantum simulation. It is a very versatile technique which allows for the emulation of interactions that do not only depend on inter-particle separations or do not decay with particle separation. We detail the proposed experimental scheme and consider two examples of interacting phenomena, self-trapping and the decay of Bloch oscillations, that are observable with the proposed technique. Graphical abstract: [Figure not available: see fulltext.]
CRIS-Team Scopus Importer:2020-05-12

Systematic analysis of crystalline phases in bosonic lattice models with algebraically decaying density-density interactions - Koziol, Jan; Duft, Antonia; Morigi, Giovanna; Schmidt, Kai Phillip (SciPost Physics, 2023)
We propose a general approach to analyse diagonal ordering patterns in bosonic lattice models with algebraically decaying density-density interactions on arbitrary lattices. The key idea is a systematic search for the energetically best order on all unit cells of the lattice up to a given extent. Using resummed couplings we evaluate the energy of the ordering patterns in the thermodynamic limit using finite unit cells. We apply the proposed approach to the atomic limit of the extended Bose-Hubbard model on the triangular lattice at fillings f = 1/2 and f = 1. We investigate the ground-state properties of the antiferromagnetic long-range Ising model on the triangular lattice and determine a six-fold degenerate plain-stripe phase to be the ground state for finite decay exponents. We also probe the classical limit of the Fendley-Sengupta-Sachdev model describing Rydberg atom arrays. We focus on arrangements where the atoms are placed on the sites or links of the Kagome lattice. Our method provides a general framework to treat cristalline structures resulting from long-range interactions.
CRIS-Team Scopus Importer:2023-06-30

Tagged-particle motion in a dense confined liquid - Lang, Simon; Franosch, Thomas (Physical Review E, 2014)
We investigate the dynamics of a tagged particle embedded in a strongly interacting confined liquid enclosed between two opposing flat walls. Using the Zwanzig-Mori projection operator formalism we obtain an equation of motion for the incoherent scattering function suitably generalized to account for the lack of translational symmetry. We close the equations of motion by a self-consistent mode-coupling ansatz. The interaction of the tracer with the surrounding liquid is encoded in generalized direct correlation functions. We extract the in-plane dynamics and provide a microscopic expression for the diffusion coefficient parallel to the walls. The solute particle may differ in size or interaction from the surrounding host-liquid constituents offering the possibility of a systematic analysis of dynamic effects on the tagged-particle motion in confinement.
EAM Import::2019-03-12

Tailoring the structure and thermoelectric properties of BaTiO3 via Eu2+ substitution - Xiao, Xingxing; Widenmeyer, Marc; Xie, Wenjie; Zou, Tianhua; Yoon, Songhak; Scavini, Marco; Checchia, Stefano; Zhong, Zhicheng; Hansmann, Philipp; Kilper, Stefan; Kovalevsky, Andrei; Weidenkaff, Anke (Physical Chemistry Chemical Physics, 2017)
A series of Ba1-xEuxTiO3-delta (0.1 <= x <= 0.9) phases with similar to 40 nm particle size were synthesized via a Pechini method followed by annealing and sintering under a reducing atmosphere. The effects of Eu2+ substitution on the BaTiO3 crystal structure and the thermoelectric transport properties were systematically investigated. According to synchrotron X-ray diffraction data only cubic perovskite structures were observed. On the local scale below about 20 angstrom (equal to similar to 5 unit cells) deviations from the cubic structure model (Pm% (3) over barm) were detected by evaluation of the pair distribution function (PDF). These deviations cannot be explained by a simple symmetry breaking model like in EuTiO3-delta. The best fit was achieved in the space group Amm2 allowing for a movement of Ti and Ba/Eu along < 110 > of the parent unit cell as observed for BaTiO3. Density functional calculations delivered an insight into the electronic structure of Ba1-xEuxTiO3-delta. From the obtained density of states a significant reduction of the band gap by the presence of filled Eu2+ 4f states at the top of the valence band was observed. The physical property measurements revealed that barium-europium titanates exhibit n-type semiconducting behavior and at high temperature the electrical conductivity strongly depended on the Eu2+ content. Activation energies calculated from the electrical conductivity and Seebeck coefficient data indicate that at high temperatures (800 K < T < 1123 K) the conduction mechanism of Ba1-xEuxTiO3-delta (0.1 <= x <= 0.9) is a polaron hopping when 0 <= x <= 0.6 and is a thermally activated process when 0.6 < x < 1. Besides, the thermal conductivity increases with increasing Eu2+ concentration. Due to a remarkable improvement of the power factor, Ba0.1Eu0.9TiO3-delta showed a ZT value of 0.24 at 1123 K.
CRIS-Team WoS Importer:2020-02-19

TANAMI blazars in the IceCube PeV-neutrino fields - Krauß, Felicia; Kadler, Matthias; Mannheim, K.; Schulz, Robert; Truestedt, J.; Wilms, Jörn; Ojha, R.; Ros, Eduardo; Anton, Gisela; Baumgartner, W.; Beuchert, Tobias; Blanchard, J.; et al. (Astronomy & Astrophysics, 2014)
The IceCube Collaboration has announced the discovery of a neutrino flux in excess of the atmospheric background. Owing to the steeply falling atmospheric background spectrum, events at PeV energies most likely have an extraterrestrial origin. We present the multiwavelength properties of the six radio-brightest blazars that are positionally coincident with these events using contemporaneous data of the TANAMI blazar sample, including high-resolution images and spectral energy distributions. Assuming the X-ray to gamma-ray emission originates in the photoproduction of pions by accelerated protons, the integrated predicted neutrino luminosity of these sources is high enough to explain the two detected PeV events.
Keywords: neutrinos; galaxies: active; quasars: general

Temperature dependence of the transition packing fraction of thermal jamming in a harmonic soft sphere system - Maiti, Moumita; Schmiedeberg, Michael (Journal of Physics: Condensed Matter, 2019)
The glassy dynamics of soft harmonic spheres are often mapped onto the dynamics of hard spheres by considering an effective diameter for the soft particles and therefore an effective packing fraction. While in this approach the thermal fluctuations within valleys of the energy landscape are covered, the crossing of energy barriers from one valley into another usually is neglected. Here we argue—motivated by studies of the glass transition based on explorations of the energy landscape—that the crossing of energy barriers can be attributed by an effective decrease of the glass transition packing fraction with increasing temperature T according to T 0.2. Furthermore, we reanalyzing data of soft sphere simulations. Since fitting scaling laws to simulation data always allows for some arbitrariness, we cannot prove based on the simulation data that our idea of a shift of the glass transition packing fraction due to barrier crossings is the only possible way to explain the discrepancies that have been observed previously. However, we show that a possible explanation of the simulation data is given by our approach to characterize the dynamics of soft spheres by both, the previously-considered temperature-dependent effective packing fraction due to the increase of the mean overlap between neighboring particles with stronger thermal fluctuations and the newly introduced increase of the glass transition packing with an increasing probability of barrier crossing
Keywords: glass transition; jamming; colloids

Temperature in one-dimensional bosonic Mott insulators - Schmidt, Kai Phillip; et al. (Physical Review A, 2005)
The Mott insulating phase of a one-dimensional bosonic gas trapped in an optical lattice is described by a Bose-Hubbard model. A continuous unitary transformation is used to map this model onto an effective model conserving the number of elementary excitations. We obtain quantitative results for the kinetics and for the spectral weights of the low-energy excitations for a broad range of parameters in the insulating phase. By these results, recent Bragg spectroscopy experiments are explained. Evidence for a significant temperature of the order of the microscopic energy scales is found.

Tensorial density functional theory for non-spherical hard-body fluids - Hansen-Goos, Hendrik; Mecke, Klaus (Journal of Physics: Condensed Matter, 2010)
In a recent publication (Hansen-Goos and Mecke 2009 Phys. Rev. Lett. 102 018302) we constructed a free energy functional for the inhomogeneous hard-body fluid, which reduces to Rosenfeld's fundamental measure theory (Rosenfeld 1989 Phys. Rev. Lett. 63 980) when applied to hard spheres. The new functional is able to yield the isotropic-nematic transition for the hard-spherocylinder fluid in contrast to Rosenfeld's fundamental measure theory for non-spherical particles (Rosenfeld 1994 Phys. Rev. E 50 R3318). The description of inhomogeneous isotropic fluids is also improved when compared with data from Monte Carlo simulations for hard spherocylinders in contact with a planar hard wall. However, the new functional for the inhomogeneous fluid in general does not comply with the exact second order virial expansion. We introduced the. correction in order to minimize the deviation from Onsager's exact result in the isotropic bulk fluid. In this article we give a detailed account of the construction of the new functional. An extension of the. correction makes the latter better suited for non-isotropic particle distributions. The extended. correction is shown to improve the description of the isotropic-nematic bulk phase diagram while it has little effect on the results for the isotropic but inhomogeneous hard-spherocylinder fluid. We argue that the gain from using higher order tensorial weighted densities in the theory is likely to be inferior to the associated increase in complexity.

Tensorial Minkowski functionals and anisotropy measures for planar patterns - Schröder-Turk, Gerd; Kapfer, Sebastian; Breidenbach, B.; Beisbart, C.; Mecke, Klaus (Journal of Microscopy, 2010)
Quantitative measures for anisotropic characteristics of spatial structure are needed when relating the morphology of microstructured heterogeneous materials to tensorial physical properties such as elasticity, permeability and conductance. Tensor-valued Minkowski functionals, defined in the framework of integral geometry, provide a concise set of descriptors of anisotropic morphology. In this article, we describe the robust computation of these measures for microscopy images and polygonal shapes. We demonstrate their relevance for shape description, their versatility and their robustness by applying them to experimental data sets, specifically microscopy data sets of non-equilibrium stationary Turing patterns and the shapes of ice grains from Antarctic cores.
Keywords: Anisotropy; integral geometry; microstructured and cellular; materials; Minkowski functionals; morphology; strain and deformation; Turing patterns

Tensorial Minkowski functionals of triply periodic minimal surfaces - Mickel, Walter; Schröder-Turk, Gerd; Mecke, Klaus (Interface Focus, 2012)
A fundamental understanding of the formation and properties of a complex spatial structure relies on robust quantitative tools to characterize morphology. Asystematic approach to the characterization of average properties of anisotropic complex interfacial geometries is provided by integral geometry which furnishes a family of morphological descriptors known as tensorial Minkowski functionals. These functionals are curvature-weighted integrals of tensor products of position vectors and surface normal vectors over the interfacial surface. We here demonstrate their use by application to non-cubic triply periodic minimal surface model geometries, whose Weierstrass parametrizations allow for accurate numerical computation of the Minkowski tensors.
Keywords: morphology; anisotropy; lipid self-assembly; minimal surface; porous material; integral geometry

Tensor-Network Codes - Farrelly, Terry; Harris, Robert J.; McMahon, Nathan; Stace, Thomas M. (Physical Review Letters, 2021)
We introduce tensor-network stabilizer codes which come with a natural tensor-network decoder. These codes can correspond to any geometry, but, as a special case, we generalize holographic codes beyond those constructed from perfect or block-perfect isometries, and we give an example that corresponds to neither. Using the tensor-network decoder, we find a threshold of 18.8% for this code under depolarizing noise. We show that, for holographic codes, the exact tensor-network decoder (with no bond-dimension truncation) has polynomial complexity in the number of physical qubits, even for locally correlated noise, making this the first efficient decoder for holographic codes against Pauli noise and, also, a rare example of a decoder that is both efficient and exact.
CRIS-Team WoS Importer:2021-08-06

Testing the master constraint programme for loop quantum gravity: I. General framework - Dittrich, Bianca; Thiemann, Thomas (Classical and Quantum Gravity, 2006)
Recently, the master constraint programme for loop quantum gravity (LQG) was proposed as a classically equivalent way to impose the infinite number of Wheeler-DeWitt constraint equations in terms of a single master equation. While the proposal has some promising abstract features, it was until now barely tested in known models. In this series of five papers we fill this gap, thereby adding confidence to the proposal. We consider a wide range of models with increasingly more complicated constraint algebras, beginning with a finite-dimensional, Abelian algebra of constraint operators which are linear in the momenta and ending with an infinite-dimensional, non-Abelian algebra of constraint operators which closes with structure functions only and which are not even polynomial in the momenta. In all these models, we apply the master constraint programme successfully; however, the full flexibility of the method must be exploited in order to complete our task. This shows that the master constraint programme has a wide range of applicability but that there are many, physically interesting Subtleties that must be taken care of in doing so. In particular, as we will see, that we can possibly construct a master constraint operator for a nonlinear, that is, interacting quantum field theory underlines the strength of the background-independent formulation of LQG. In this first paper, we prepare the analysis of our test models by outlining the general framework of the master constraint programme. The models themselves will be studied in the remaining four papers. As a side result, we develop the direct integral decomposition (DID) programme for solving quantum constraints as an alternative to refined algebraic quantization (RAQ).

Testing the master constraint programme for loop quantum gravity: II. Finite-dimensional systems - Dittrich, Bianca; Thiemann, Thomas (Classical and Quantum Gravity, 2006)
This is the second paper in our series of five in which we test the master constraint programme for solving the Hamiltonian constraint in loop quantum gravity. In this work, we begin with the simplest examples: finite-dimensional models with a finite number of first or second class constraints, Abelian or non-Abelian, with or without structure functions.

Testing the master constraint programme for loop quantum gravity: III. SL(2, R) models - Thiemann, Thomas; Dittrich, Bianca (Classical and Quantum Gravity, 2006)
This is the third paper in our series of five in which we test the master constraint programme for solving the Hamiltonian constraint in loop quantum gravity. In this work, we analyse models which, despite the fact that the phase space is finite dimensional, are much more complicated than in the second paper. These are systems with an SL(2, R) gauge symmetry and the complications arise because non-compact semisimple Lie groups are not amenable (have no finite translation invariant measure). This leads to severe obstacles in the refined algebraic quantization programme (group averaging) and we see a trace of that in the fact that the Spectrum of the master constraint does not contain the point zero. However, the minimum of the spectrum is of order h 2 which can be interpreted as a normal ordering constant arising from first class constraints (while second class systems lead to h normal ordering constants). The physical Hilbert space can then be obtained after subtracting this normal ordering correction.

Testing the master constraint programme for loop quantum gravity: IV. Free field theories - Dittrich, Bianca; Thiemann, Thomas (Classical and Quantum Gravity, 2006)
This is the fourth paper in Our series of five in which we test the master constraint programme for solving the Hamiltonian constraint in loop quantum gravity. We now move oil to free field theories with constraints, namely Maxwell theory and linearized gravity. Since the master constraint involves squares of constraint operator valued distributions, one has to be very careful in doing that and we will see that the full flexibility of the master constraint programme must be exploited in order to arrive at sensible results.

Testing the master constraint programme for loop quantum gravity: V. Interacting field theories - Dittrich, Bianca; Thiemann, Thomas (Classical and Quantum Gravity, 2006)
This is the fifth and final paper in our series of five in which we test the master constraint programme for solving the Hamiltonian constraint in loop quantum gravity. Here we consider interacting quantum field theories, specifically we consider the non-Abelian Gauss constraints of Einstein-Yang-Mills theory and 2+1 gravity. Interestingly, while Yang-Mills theory in 4D is not yet rigorously defined as ail ordinary (Wightman) quantum field theory oil Minkowski space, in background-independent quantum field theories such as loop quantum gravity (LQG) this might become possible by working in a new, background-independent representation. While for the Gauss Constraint the master constraint can be solved explicitly, for the 2+1 theory we are only able to rigorously define the master constraint operator. We show that the, by other methods known, physical Hilbert is contained in the kernel of the master constraint, however, to systematically derive it by Only using spectral methods is as complicated as for 3+1 gravity and we therefore leave the complete analysis for 3+1 gravity.

Th 229m isomer from a nuclear model perspective - Minkov, Nikolay; Palffy-Buß, Adriana (Physical Review C - Nuclear Physics, 2021)
The physical conditions for the emergence of the extremely low-lying nuclear isomer Th229m at approximately 8 eV are investigated in the framework of our recently proposed nuclear structure model. Our theoretical approach explains the Th229m-isomer phenomenon as the result of a very fine interplay between collective quadrupole-octupole and single-particle dynamics in the nucleus. We find that the isomeric state can only appear in a rather limited model space of quadrupole-octupole deformations in the single-particle potential, with the octupole deformation being of a crucial importance for its formation. Within this deformation space the model-described quantities exhibit a rather smooth behavior close to the line of isomer-ground-state quasidegeneracy determined by the crossing of the corresponding single-particle orbitals. Our comprehensive analysis confirms the previous model predictions for reduced transition probabilities and the isomer magnetic moment, while showing a possibility for limited variation in the ground-state magnetic moment theoretical value. These findings prove the reliability of the model and suggest that the same dynamical mechanism could manifest in other actinide nuclei giving a general prescription for the search and exploration of similar isomer phenomena.
CRIS-Team Scopus Importer:2021-02-05

The ANTARES telescope neutrino alert system - Ageron, M.; Aguilar, J. A.; Al Samarai, I.; Albert, A.; Andre, Michel; Anghinolfi, M.; Anton, Gisela; Anvar, S.; Ardid, Miguel; Jesus, A. C. Assis; Astraatmadja, T.; Aubert, J. -J.; et al. (Astroparticle Physics, 2012)
The ANTARES telescope has the capability to detect neutrinos produced in astrophysical transient sources. Potential sources include gamma-ray bursts, core collapse supernovae, and flaring active galactic nuclei. To enhance the sensitivity of ANTARES to such sources, a new detection method based on coincident observations of neutrinos and optical signals has been developed. A fast online muon track reconstruction is used to trigger a network of small automatic optical telescopes. Such alerts are generated for special events, such as two or more neutrinos, coincident in time and direction, or single neutrinos of very high energy. (C) 2011 Elsevier B.V. All rights reserved.
Keywords: ANTARES; Neutrino astronomy; Transient sources; Optical follow-up

The Free Energy of a Quantum Sherrington–Kirkpatrick Spin-Glass Model for Weak Disorder - Leschke, Hajo; Rothlauf, Sebastian; Ruder, Rainer; Spitzer, Wolfgang (Journal of Statistical Physics, 2021)
We extend two rigorous results of Aizenman, Lebowitz, and Ruelle in their pioneering paper of 1987 on the Sherrington–Kirkpatrick spin-glass model without external magnetic field to the quantum case with a “transverse field” of strength b. More precisely, if the Gaussian disorder is weak in the sense that its standard deviation v> 0 is smaller than the temperature 1 / β, then the (random) free energy almost surely equals the annealed free energy in the macroscopic limit and there is no spin-glass phase for any b/ v≥ 0. The macroscopic annealed free energy turns out to be non-trivial and given, for any βv> 0 , by the global minimum of a certain functional of square-integrable functions on the unit square according to a Varadhan large-deviation principle. For βv< 1 we determine this minimum up to the order (βv) 4 with the Taylor coefficients explicitly given as functions of βb and with a remainder not exceeding (βv) 6/ 16. As a by-product we prove that the so-called static approximation to the minimization problem yields the wrong βb-dependence even to lowest order. Our main tool for dealing with the non-commutativity of the spin-operator components is a probabilistic representation of the Boltzmann–Gibbs operator by a Feynman–Kac (path-integral) formula based on an independent collection of Poisson processes in the positive half-line with common rate βb. Its essence dates back to Kac in 1956, but the formula was published only in 1989 by Gaveau and Schulman.
CRIS-Team Scopus Importer:2021-03-19
Keywords: Annealed free energy; Feynman–Kac formula; Quantum spin-glas model; Varadhan large-deviation principle

The Hessian in Spin Foam Models - Kamiński, Wojciech; Sahlmann, Hanno (Annales Henri Poincaré, 2019)
We fill one of the remaining gaps in the asymptotic analysis of the vertex amplitudes of the Engle–Pereira–Rovelli–Livine (EPRL) spin foam models: We show that the Hessian is nondegenerate for the stationary points that corresponds to geometric nondegenerate 4 simplices. Our analysis covers the case when all faces are spacelike.
CRIS-Team Scopus Importer:2019-10-29

The holonomy-flux algebra in low dimensions - Frembs, Markus; Sahlmann, Hanno (2013)
We derive the commutation relations of the holonomy-flux algebra in general for any dimension and gauge group. We explicitly calculate those for the case of two dimensions and one dimension. We generalize the intersection number which occurs for every commutator of holonomies and fluxes to certain equivalence classes of loops resembling homotopy classes before we start with the discussion of representations for holonomy-flux-algebras. In the case of two dimensions we discover some interesting parallels to the canonical commutation relations. We find the dual Ashtekar-Lewandowski-representation and also define the transformation rule which, just as the Fourier transformation in quantum mechanics, translates between the Ashtekar- Lewandowski-representation and its dual. We finally show that in two dimensions and for the abelian case, holonomy-flux-algebras can be related to Weyl algebras in a simple way.

The Holst spin foam model via cubulations - Baratin, Aristide; Flori, Cecilia; Thiemann, Thomas (New Journal of Physics, 2012)
Spin foam models are an attempt at a covariant or path integral formulation of canonical loop quantum gravity. The construction of such models usually relies on the Plebanski formulation of general relativity as a constrained BF theory and is based on the discretization of the action on a simplicial triangulation, which may be viewed as an ultraviolet regulator. The triangulation dependence can be removed by means of group field theory techniques, which allows one to sum over all triangulations. The main tasks for these models are the correct quantum implementation of the Plebanski constraints, the existence of a semiclassical sector implementing additional 'Regge-like' constraints arising from simplicial triangulations and the definition of the physical inner product of loop quantum gravity via group field theory. Here we propose a new approach to tackle these issues stemming directly from the Holst action for general relativity, which is also a proper starting point for canonical loop quantum gravity. The discretization is performed by means of a 'cubulation' of the manifold rather than a triangulation. We give a direct interpretation of the resulting spin foam model as a generating functional for the n-point functions on the physical Hilbert space at finite regulator. This paper focuses on ideas and tasks to be performed before the model can be taken seriously. However, our analysis reveals some interesting features of this model: firstly, the structure of its amplitudes differs from the standard spin foam models. Secondly, the tetrad n-point functions admit a 'Wick-like' structure. Thirdly, the restriction to simple representations does not automatically occur-unless one makes use of the time gauge, just as in the classical theory.

The ideas of Kaluza and Klein in the context of loop quantum gravity - Wichert, Josef; Sahlmann, Hanno (Friedrich-Alexander-Universität Erlangen-Nürnberg, 2018)

The Impact of Rate Formulations on Stochastic Molecular Motor Dynamics - Blackwell, Robert; Jung, Wieland David Krischan; Bukenberger, M.; Smith, Ana-Suncana (Scientific Reports, 2019)
Cells are complex structures which require considerable amounts of organization via transport of large intracellular cargo. While passive diffusion is often sufficiently fast for the transport of smaller cargo, active transport is necessary to organize large structures on the short timescales necessary for biological function. The main mechanism of this transport is by cargo attachment to motors which walk in a directed fashion along intracellular filaments. There are a number of models which seek to describe the motion of motors with attached cargo, from detailed microscopic to coarse phenomenological descriptions. We focus on the intermediate-detailed discrete stochastic hopping models, and explore how cargo transport changes depending on the number of motors, motor interaction, system constraints and rate formulations, which are derived from common thermodynamic assumptions. We find that, despite obeying the same detailed balance constraint, the choice of rate formulation considerably affects the characteristics of the overall motion of the system, with one rate formulation exhibiting novel behavior of loaded motor groups moving faster than a single unloaded motor.
CRIS-Team Scopus Importer:2019-12-20

The Influence of Chemical Change on Protein Dynamics: A Case Study with Pyruvate Formate-Lyase - Hanzevacki, Marko; Čondić-Jurkić, Karmen; Banhatti, Radha Dilip; Smith, Ana-Suncana; Smith, David M. (Chemistry - A European Journal, 2019)
Pyruvate formate-lyase (PFL) catalyzes the reversible conversion of pyruvate and coenzyme A (CoA) into formate and acetyl-CoA in two half-reactions. For the second half-reaction to take place, the S−H group of CoA must enter the active site of the enzyme to retrieve a protein-bound acetyl group. However, CoA is bound at the protein surface, whereas the active site is buried in the protein interior, some 20–30 Å away. The PFL system was therefore subjected to a series of extensive molecular dynamics simulations (in the μs range) and a host of advanced analysis procedures. Models representing PFL before and after the first half-reaction were used to examine the possible effect of enzyme acetylation. All simulated structures were found to be relatively stable compared to the initial crystal structure. Although the adenine portion of CoA remained predominantly bound at the protein surface, the binding of the S−H group was significantly more labile. A potential entry channel for CoA, which would allow the S−H group to reach the active site, was identified and characterized. The channel was found to be associated with accentuated fluctuations and a higher probability of being in an open state in acetylated systems. This result suggests that the acetylation of the enzyme assumes a prominent functional role, whereby the formation of the acyl intermediate serves to initiate a subtle signaling cascade that influences the protein dynamics and facilitates the entry of the second substrate.
CRIS-Team Scopus Importer:2019-05-24
Keywords: coenzyme A; molecular dynamics; protein dynamics; pyruvate formate-lyase; radical enzymes

The inverse loop transform - Thiemann, Thomas (Journal of Mathematical Physics, 1998)
The loop transform in quantum gauge field theory can be recognized as the Fourier transform (or characteristic functional) of a measure on the space of generalized connections module gauge transformations. Since this space is a compact Hausdorff space, conversely, we know from the Riesz-Markov theorem that every positive linear functional on the space of continuous functions thereon qualifies as the loop transform of a regular Borel measure on the moduli space. In the present article we show how one can compute the finite joint distributions of a given characteristic functional, that is, we derive the inverse loop transform. (C) 1998 American Institute of Physics. [S002-2488(98)00302-8].

The Lewis-Riesenfeld Invariant in the context of a Loop Quantum Cosmology quantisation - Matas, Bystrik; Giesel, Kristina; Kobler, Michael (2018)

The LQG string - loop quantum gravity quantization of string theory: I. Flat target space - Thiemann, Thomas (Classical and Quantum Gravity, 2006)
We combine (i) background-independent loop quantum gravity (LQG) quantization techniques, (ii) the mathematically rigorous framework of algebraic quantum field theory (AQFT) and (iii) the theory of integrable systems resulting in the invariant Pohlmeyer charges in order to set up the general representation theory (superselection theory) for the closed bosonic quantum string on flat target space. While we do not solve the, expectedly, rich representation theory completely, we present a, to the best of our knowledge, new, non-trivial solution to the representation problem. This solution exists (1) for any target space dimension, (2) for Minkowski signature of the target space, (3) without tachyons, (4) manifestly ghost free (no negative norm states), (5) without fixing a worldsheet or target space gauge, (6) without (Virasoro) anomalies (zero central charge), (7) while preserving manifest target space Poincare invariance and (8) without picking up UV divergences. The existence of this stable solution is, on one hand, exciting because it raises the hope that among all the solutions to the representation problem (including fermionic degrees of freedom) we find stable, phenomenologically acceptable ones in lower dimensional target spaces, possibly without supersymmetry, that are much simpler than the solutions that arise via compactification of the standard Fock representation of the string. On the other hand, if such solutions are found, then this would prove that neither a critical dimension (D = 10, 11, 26) nor supersymmetry is a prediction of string theory. Rather, these would be features of the particular Fock representation of current string theory and hence would not be generic. The solution presented in this paper exploits the flatness of the target space in several important ways. In a companion paper, we treat the more complicated case of curved target spaces.

The microlocal spectrum condition, initial value formulations, and background independence - Stottmeister, Alexander; Thiemann, Thomas (Journal of Mathematical Physics, 2016)
We analyze implications of the microlocal spectrum/Hadamard condition for states in a (linear) quantum field theory on a globally hyperbolic spacetime M in the context of a (distributional) initial value formulation. More specifically, we work in 3+1-split M congruent to R x Sigma and give a bound, independent of the spacetime metric, on the wave front sets of the initial data for a quasi-free Hadamard state in a quantum field theory defined by a normally hyperbolic differential operator P acting in a vector bundle E ->(pi) M. This aims at a possible way to apply the concept of Hadamard states within approaches to quantum field theory/gravity relying on a Hamiltonian formulation, potentially without a (classical) background metric g. (C) 2016 AIP Publishing LLC.

The microscopic structure of mono-disperse granular heaps and sediments of particles on inclined surfaces - Topic, Nikola; Schaller, Fabian; Schröder-Turk, Gerd; Pöschel, Thorsten (Soft Matter, 2016)
Granular heaps of particles created by deposition of mono-disperse particles raining from an extended source of finite size are characterized by a non-homogeneous field of density. It was speculated that this inhomogeneity is due to the transient shape of the sediment during the process of construction of the heap, thus reflecting the history of the creation of the heap. By comparison of structural characteristics of the heap with sediments created on top of inclined planes exploiting the method of Minkowski tensors, we provide further evidence to support this hypothesis. Moreover, for the case of sediments generated by homogeneous rain on surfaces, we provide relationships between the inclination of the surface and the Minkowski measures characterizing the isotropy of local particle environments.

The no-boundary measure in scalar-tensor gravity - Sahlmann, Hanno; Yeom, Dong-han; Hwang, Dong-il (Classical and Quantum Gravity, 2012)
In this paper, we study the no-boundary wavefunction in scalartensor gravity with various potentials for the non-minimally coupled scalar field. Our goal is to calculate probabilities for the scalar fieldand hence the effective gravitational coupling and cosmological constantto take specific values. Most calculations are performed in the minisuperspace approximation, and we use a saddle point approximation for the Euclidean action, which is then evaluated numerically. We find that for potentials that have several minima, none of them is substantially preferred by the quantum-mechanical probabilities. We argue that the same is true for the stable and the runaway solution in the case of a dilaton-type potential. Technically, this is due to the inclusion of quantum-mechanical effects (fuzzy instantons). These results are in contrast to the often-held view that vanishing gravitation or cosmological constants would be exponentially preferred in quantum cosmology, and they may be relevant to the cosmological constant problem and the dilaton stabilization problem. © 2012 IOP Publishing Ltd.

The no-boundary measure in string theory: Applications to moduli stabilization, flux compactification and cosmic landscape - Hwang, Dong-il; Lee, Bum-Hoon; Sahlmann, Hanno; Yeom, Dong-han (Classical and Quantum Gravity, 2012)
We investigate the no-boundary measure in the context of moduli stabilization. To this end, we first show that for exponential potentials, there are no classical histories once the slope exceeds a critical value. We also investigate the probability distributions given by the no-boundary wavefunction near maxima of the potential. These results are then applied to a simple model that compactifies 6D to 4D (HBSV model) with fluxes. We find that the no-boundary wavefunction effectively stabilizes the moduli of the model. Moreover, we find the a priori probability for the cosmological constant in this model. We find that a negative value is preferred, and a vanishing cosmological constant is not distinguished by the probability measure. We also discuss the application to the cosmic landscape. Our preliminary arguments indicate that the probability of obtaining anti-de Sitter space is vastly greater than that for de Sitter. © 2012 IOP Publishing Ltd.

Theoretical framework for two-microswimmer hydrodynamic interactions - Ziegler, Sebastian; Scheel, Thomas; Hubert, Maxime; Harting, Jens; Smith, Ana-Suncana (New Journal of Physics, 2021)
Hydrodynamic interactions are crucial for determining the cooperative behavior of microswimmers at low Reynolds numbers. Here we provide a comprehensive analysis of the scaling laws and the strength of the interactions in the case of a pair of three-sphere swimmers. Both stroke-based and force-based elastic microswimmers are analyzed using an analytic perturbative approach, focusing on passive and active interactions. The former are governed by the cycle-averaged flow field of a single swimmer, which is dipolar at long range. However, at intermediate distances, with a cross-over at the order of 10(2) swimmer lengths, the quadrupolar field dominates which, notably, yields an increase of the swimming velocity compared to individual swimmers, even when the swimmers are one behind another. Furthermore, we find that active rotations resulting from the interplay of the time-resolved swimming stroke and the ambient flow fields and, even more prominently, active translations are model-dependent. A mapping between the stroke-based and force-based swimmers is only possible for the low driving frequency regime where the characteristic time scale is smaller than the viscous one. Finally, we find that the long-term behavior of the swimmers, while sensitive to the initial relative positioning, does not depend on the pusher or puller nature of the swimmer. These results clearly indicate that the behavior of swarms will depend on the swimmer model, which was hitherto not well appreciated.
CRIS-Team WoS Importer:2021-08-13

Theoretical Prediction and Spectroscopic Fingerprints of an Orbital Transition in CeCu2Si2 - Pourovskii, L. V.; Hansmann, Philipp; Ferrero, Michel; Georges, Antoine (Physical Review Letters, 2014)
We show that the heavy-fermion compound CeCu2Si2 undergoes a transition between two regimes dominated by different crystal-field states. At low pressure P and low temperature T the Ce 4f electron resides in the atomic crystal-field ground state, while at high P or T, the electron occupancy and spectral weight is transferred to an excited crystal-field level that hybridizes more strongly with itinerant states. These findings result from first-principles dynamical-mean-field-theory calculations. We predict experimental signatures of this orbital transition in x-ray spectroscopy. The corresponding fluctuations may be responsible for the second high-pressure superconducting dome observed in this and similar materials.
CRIS-Team WoS Importer:2020-02-19

Theory of Magnetization Plateaux in the Shastry-Sutherland Model - Dorier, J.; Schmidt, Kai Phillip; Mila, F. (Physical Review Letters, 2008)
Motivated by the remarkable properties of SrCu(2)(BO(3))(2) in a magnetic field, we use perturbative continuous unitary transformations to determine the magnetization plateaux of the Shastry-Sutherland model, unveiling an unexpected sequence of plateaux progressively appearing at 2/9, 1/6, 1/9, and 2/15 upon increasing the interdimer coupling. We predict that a 1/6 plateau should be present in SrCu(2)(BO(3))(2), even if residual interactions beyond the Shastry-Sutherland are strong enough to modify the other plateaux below 1/3. The method is extended to calculate the magnetization profile within the plateaux, leading to a local structure around triplons that agrees with NMR results on SrCu(2)(BO(3))(2).

The Phoenix Project: master constraint programme for loop quantum gravity - Thiemann, Thomas (Classical and Quantum Gravity, 2006)
The Hamiltonian constraint remains the major unsolved problem in loop quantum gravity (LQG). Some time ago, a mathematically consistent candidate Hamiltonian constraint was proposed but there are still several unsettled questions which concern the algebra of commutators among smeared Hamiltonian constraints which must be faced in order to make progress. In this paper, we propose a solution to this set of problems based on the so-called master constraint which combines the smeared Hamiltonian constraints for all smearing functions into a single constraint. Due to a harmonic interplay of several mathematical facts, the problems with the commutator algebra disappear and chances are good that one can control the solution space and the (quantum) Dirac observables of LQG. Even a decision on whether the theory has the correct classical limit and a connection with the path integral (or spin foam) formulation could be in reach.

The Physical Hamiltonian of the Gowdy Model in Algebraic Quantum Gravity - Böhm, Benedikt; Giesel, Kristina (Friedrich-Alexander-Universität Erlangen-Nürnberg, 2015)

The positioning system of the ANTARES Neutrino Telescope - Adrian-Martinez, S.; Ageron, M.; Aguilar, J. A.; Al Samarai, I.; Albert, A.; Andre, Michel; Anghinolfi, M.; Anton, Gisela; Anvar, S.; Ardid, Miguel; Jesus, A. C. Assis; Astraatmadja, T.; et al. (Journal of Instrumentation, 2012)
The ANTARES neutrino telescope, located 40km off the coast of Toulon in the Mediterranean Sea at a mooring depth of about 2475m, consists of twelve detection lines equipped typically with 25 storeys. Every storey carries three optical modules that detect Cherenkov light induced by charged secondary particles (typically muons) coming from neutrino interactions. As these lines are flexible structures fixed to the sea bed and held taut by a buoy, sea currents cause the lines to move and the storeys to rotate. The knowledge of the position of the optical modules with a precision better than 10cm is essential for a good reconstruction of particle tracks. In this paper the ANTARES positioning system is described. It consists of an acoustic positioning system, for distance triangulation, and a compass-tiltmeter system, for the measurement of the orientation and inclination of the storeys. Necessary corrections are discussed and the results of the detector alignment procedure are described.
Keywords: Timing detectors; Detector modelling and simulations II (electric fields; charge transport; multiplication and induction; pulse formation; electron emission; etc); Detector alignment and calibration methods (lasers; sources; particle-beams); Detector control systems (detector and experiment monitoring and slow-control systems; architecture; hardware; algorithms; databases)

The Protonation States of the Active-Site Histidines in (6-4) Photolyase - Condic-Jurkic, Karmen; Smith, Ana-Suncana; Zipse, Hendrik; Smith, David M. (Journal of Chemical Theory and Computation, 2012)
The active sites of the (6-4) photolyases contain two conserved histidine residues, which, in the Drosophila melanogaster enzyme, correspond to His365 and His369. While there are nine combinations in which the three possible protonation states of the two histidines (with protons on N delta (HID), N epsilon (HIE), or both N delta and N epsilon (HIP)) can be paired, there is presently no consensus as to which of these states is present, let alone mechanistically relevant. EPR hyperfine couplings for selected protons of the FADH* radical have previously been used to address this issue. Our QM/MM calculations show, however, that the experimental couplings are equally well reproduced by each of the nine combinations. Since the EPR results seemingly cannot be used to unequivocally assign the protonation states, the pK(a) values of the two histidines were calculated using the popular PROPKA, H++, and APBS approaches in various environments and for several lesions. These techniques consistently indicate that, at pH = 7, both His365 and His369 should be neutral, although His369 is found to be more prone to becoming protonated. In a comparative approach, a series of molecular dynamics simulations was performed with all nine combinations, employing various reference crystal structures and different oxidation states of the FAD cofactor. The overall result of this approach is in agreement with our pKa results. Consequently, although the introduction of the reduced cofactor results in an increased stability for selected protonated states, particularly the His365=HID and His369=HIP combination, the neutral combination His365=HID and His365=HIE stands out as the most relevant state for the activity of the enzyme.
Keywords: DIMER RADICAL-ANION; AMBER FORCE-FIELD; DNA PHOTOLYASE; MECHANICAL CALCULATIONS; MOLECULAR-DYNAMICS; CRYSTAL-STRUCTURE; ELECTRON-TRANSFER; NUCLEIC-ACIDS; PK(A) VALUES; RESP MODEL

THE REDUCED PHASE-SPACE OF SPHERICALLY SYMMETRICAL EINSTEIN-MAXWELL THEORY INCLUDING A COSMOLOGICAL CONSTANT - Thiemann, Thomas (Nuclear Physics B, 1995)
We investigate several conceptual and technical details that might be of interest for full (3 + 1) gravity. We use the new canonical variables introduced by Ashtekar, which simplifies the analysis tremendously.

Thermal fluctuations of thin liquid films - Mecke, Klaus (Journal of Physics: Condensed Matter, 2001)
A surprising lowering of the surface energy of liquid surfaces was recently found in x-ray scattering experiments which enhances thermal fluctuations of fluid interfaces at microscopic scales and calls for a re-examination of small-scale interfacial processes. This reduction was predicted for microscopic undulations below a few nm by density functional theory taking into account the long-range attraction of molecular interaction potentials. Here, a self-consistent theory is proposed for the fluctuation of fluid interfaces in arbitrary potentials which can significantly alter thermodynamical and structural properties of liquid drops, thin films, or membranes near a substrate. The substrate-induced hindrance of thermally excited capillary waves increases considerably the thickness of thin liquid films, which cannot be neglected in the analysis of adsorption data. An explicit expression for adsorption isotherms is given depending on temperature, Hamaker constant A, and surface tension gamma which takes into account the influence of capillary waves on the thickness of the fluid film and removes reported discrepancies with the Lifshitz theory of van der Waals forces. Also the steric repulsion potential of a membrane at distance D from a hard wall can be calculated self-consistently in excellent agreement with Monte Carlo simulations.

Thermal noise influences fluid flow in thin films during spinodal dewetting - Mecke, Klaus; et al. (Physical Review Letters, 2007)
Experiments on dewetting thin polymer films confirm the theoretical prediction that thermal noise can strongly influence characteristic time scales of fluid flow and cause coarsening of typical length scales. Comparing the experiments with deterministic simulations, we show that the Navier-Stokes equation has to be extended by a conserved bulk noise term to accomplish the observed spectrum of capillary waves. Because of thermal fluctuations the spectrum changes from an exponential to a power law decay for large wave vectors. Also the time evolution of the typical wave vector of unstable perturbations exhibits noise-induced coarsening that is absent in deterministic hydrodynamic flow.

Thermo-acoustic sound generation in the interaction of pulsed proton and laser beams with a water target - Lahmann, Robert; Anton, Gisela; Graf, Kay; Hossl, J.; Kappes, Alexander; Katz, Uli; Mecke, Klaus; Schwemmer, S. (Astroparticle Physics, 2015)
The generation of hydrodynamic radiation in interactions of pulsed proton and laser beams with matter is explored. The beams were directed into a water target and the resulting acoustic signals were recorded with pressure sensitive sensors. Measurements were performed with varying pulse energies, sensor positions, beam diameters and temperatures. The obtained data are matched by simulation results based on the thermo-acoustic model with uncertainties at a level of 10%. The results imply that the primary mechanism for sound generation by the energy deposition of particles propagating in water is the local heating of the medium. The heating results in a fast expansion or contraction and a pressure pulse of bipolar shape is emitted into the surrounding medium. An interesting, widely discussed application of this effect could be the detection of ultra-high energetic cosmic neutrinos in future large-scale acoustic neutrino detectors. For this application a validation of the sound generation mechanism to high accuracy, as achieved with the experiments discussed in this article, is of high importance.
Keywords: Acoustic neutrino detection; Beam interaction; Cosmic neutrinos; Thermo-acoustic model; Ultra-high energy cosmic rays

Thermodynamic properties of spin ladders with cyclic exchange - Schmidt, Kai Phillip; et al. (Physical Review B, 2003)
By high-temperature series expansion and exact complete diagonalization the magnetic susceptibility chi(T) and the specific heat C(T) of a two-leg S=1/2 ladder with cyclic (four-spin) exchange are computed. Both methods yield convincing results for not too small temperatures. We find that a small amount of cyclic exchange influences the thermodynamic properties significantly. Our results can serve as reliable basis for an efficient analysis of experimental data.

Thermodynamics of adiabatically loaded cold bosons in the Mott insulating phase of one-dimensional optical lattices - Schmidt, Kai Phillip; et al. (European Physical Journal D, 2006)
In this work we give a consistent picture of the thermodynamic properties of bosons in the Mott insulating phase when loaded adiabatically into one-dimensional optical lattices. We find a crucial dependence of the temperature in the optical lattice on the doping level of the Mott insulator. In the undoped case, the temperature is of the order of the large onsite Hubbard interaction. In contrast, at a finite doping level the temperature jumps almost immediately to the order of the small hopping parameter. These two situations are investigated on the one hand by considering limiting cases like the atomic limit and the case of free fermions. On the other hand, they are examined using a quasi-particle conserving continuous unitary transformation extended by an approximate thermodynamics for hardcore particles.

Thermodynamics of continuous non-Markovian feedback control - Debiossac, Maxime; Grass, David; Alonso Castaneda, Jose Joaquin; Lutz, Eric; Kiesel, Nikolai (Nature Communications, 2020)
Feedback control mechanisms are ubiquitous in science and technology, and play an essential role in regulating physical, biological and engineering systems. The standard second law of thermodynamics does not hold in the presence of measurement and feedback. Most studies so far have extended the second law for discrete, Markovian feedback protocols; however, non-Markovian feedback is omnipresent in processes where the control signal is applied with a non-negligible delay. Here, we experimentally investigate the thermodynamics of continuous, time-delayed feedback control using the motion of an optically levitated, underdamped microparticle. We test the validity of a generalized second law which bounds the energy extracted from the system, and study the breakdown of feedback cooling for very large time delays.
CRIS-Team Scopus Importer:2020-03-27

Thermoelectricity of near-resonant tunnel junctions and their relation to Carnot efficiency - Popp, Matthias Albert; Erpenbeck, André; Weber, Heiko B. (Scientific Reports, 2021)

The role of vibrations in single-molecule charge transport: A case study of oligoynes with pyridine anchor groups - Ballmann, Stefan Dieter; Hieringer, Wolfgang; Härtle, Rainer; Brana Coto, Pedro; Bryce, Martin; Görling, Andreas; Thoss, Michael; Weber, Heiko B. (physica status solidi (b), 2013)
We report on measurements on molecular wires in single-molecule junctions. The target is to identify vibrational signatures in the differential conductance spectra, which cannot be resolved for most molecular wires in the resonant transport regime. For the given molecules, we find indeed vibrational sidepeaks, which can be assigned to the longitudinal modes of the string-like central motif of the molecule by comparison with density functional theory. These data corroborate that oligoyne wires are ideally suited for characterizing vibrational sidepeaks. A current increase as a consequence of vibrational decoherence observed for thiols is, however, not found due to the pyridine anchor group chosen in the present molecules. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The Schrödinger Equation of the Gowdy Model in Reduced Algebraic Quantum Gravity - Leitherer, Andreas; Giesel, Kristina (Friedrich-Alexander-Universität Erlangen-Nürnberg, 2017)

The shape of parallel surface: porous media, fluctuating interfaces and complex fluids - Mecke, Klaus (ELSEVIER SCIENCE BV, 2002)
The morphological concept of parallel surfaces in combination with curvature measures ,known from integral geometry are used to characterise and model complex spatial structures beyond the two-point correlation function and to predict for instance, percolation thresholds in porous media. Applied to liquid interfaces one :finds :a;reduction of the surface tension at microscopic scales in good agreement with X-ray scattering experiments. (C) 2002 Elsevier Science B.V. All fights reserved.

The Spin-Boson Model with a time-dependent Oscillator Environment - Banarescu, Marvin; Kobler, Michael; Giesel, Kristina (2021)

The status of diffeomorphism superselection in euclidean 2+1 gravity - Marolf, Donald; Mourao, José Manuel; Thiemann, Thomas (Journal of Mathematical Physics, 1997)
This work addresses a specific technical question of relevance to canonical quantization of gravity using the so-called new variables and loop-based techniques of Ashtekar, Rovelli, and Smolin. In particular, certain ''superselection laws'' that arise in current applications of these techniques to solving the diffeomorphism constraint are considered, Their status is elucidated by studying an analogous system: 2 + 1 Euclidean gravity, For that system, these superselection laws are shown to be spurious. This, however, is only a technical difficulty. The usual quantum theory may still be obtained from a loop representation and the technique known as ''Refined Algebraic Quantization.'' (C) 1997 American Institute of Physics.

The Stokes–Einstein–Sutherland Equation at the Nanoscale Revisited - Baer, Andreas; Wawra, Simon; Bielmeier, Kristina; Uttinger, Maximilian; Smith, David M.; Peukert, Wolfgang; Walter, Johannes; Smith, Alexander Kingsbury (Small, 2023)
The Stokes–Einstein–Sutherland (SES) equation is at the foundation of statistical physics, relating a particle's diffusion coefficient and size with the fluid viscosity, temperature, and the boundary condition for the particle-solvent interface. It is assumed that it relies on the separation of scales between the particle and the solvent, hence it is expected to break down for diffusive transport on the molecular scale. This assumption is however challenged by a number of experimental studies showing a remarkably small, if any, violation, while simulations systematically report the opposite. To understand these discrepancies, analytical ultracentrifugation experiments are combined with molecular simulations, both performed at unprecedented accuracies, to study the transport of buckminsterfullerene C60 in toluene at infinite dilution. This system is demonstrated to clearly violate the conditions of slow momentum relaxation. Yet, through a linear response to a constant force, the SES equation can be recovered in the long time limit with no more than 4% uncertainty both in experiments and in simulations. This nonetheless requires partial slip on the particle interface, extracted consistently from all the data. These results, thus, resolve a long-standing discussion on the validity and limits of the SES equation at the molecular scale.
CRIS-Team Scopus Importer:2023-10-20
Keywords: analytical ultracentrifugation; boundary condition; Green–Kubo formalism; molecular dynamics; Stokes–Einstein–Sutherland equation

The structure of operators in effective particle-conserving models - Schmidt, Kai Phillip; et al. (Journal of Physics A: Mathematical and General, 2003)
For many-particle systems defined on lattices we investigate the global structure of effective Hamiltonians and observables obtained by means of a suitable basis transformation. We study transformations which lead to effective Hamiltonians conserving the number of excitations. The same transformation must be used to obtain effective observables. The analysis of the structure shows that effective operators give rise to a simple and intuitive perspective on the initial problem. The systematic calculation of n-particle irreducible quantities becomes possible constituting a significant progress. Details on how to implement the approach perturbatively for a large class of systems are presented.

The thermal jamming transition of soft harmonic disks in two dimensions - Maiti, Moumita; Schmiedeberg, Michael (European Physical Journal E, 2019)
By exploring the properties of the energy landscape of a bidisperse system of soft harmonic disks in two dimensions we determine the thermal jamming transition. To be specific, we study whether the ground state of the system where the particle do not overlap can be reached within a reasonable time. Starting with random initial configurations, the energy landscape is probed by energy minimization steps as in case of athermal jamming and in addition steps where an energy barrier can be crossed with a small but non-zero probability. For random initial conditions we find that as a function of packing fraction the thermal jamming transition, i.e. the transition from a state where all overlaps can be removed to an effectively non-ergodic state where one cannot get rid of the overlaps, occurs at a packing fraction of φ_G=0.74, which is smaller than the transition packing fraction of athermal jamming at φ_J=0.842. Furthermore, we show that the thermal jamming transition is in the universality class of directed percolation and therefore is fundamentally different from the athermal jamming transition.<br
Keywords: Jamming Glass Transition

The total solute-water correlation function for Lennard-Jones particles - Smith, Ana-Suncana; et al. (Fizika A (Zagreb), 2005)
A series of molecular dynamic simulations have been performed in order to evaluate the Lennard-Jones particle-water correlation function for solutes ranging in size from 0.3 to 1.2 nm. The results of these simulations have provided evidence for distinct orientational ordering of water molecules with respect to the solute. Furthermore, this orientational ordering is determined to be longer in range than the well-known radial ordering. Although the distance from the solute at which the correlation with water can be detected is independent of the size of the solute, the amplitude of the correlation function is sensitive to the size in the first hydration shell.
Keywords: solute-water correlation function; molecular dynamic simulations; Lennard-Jones particle