Photonic Activation Function Using Sound Waves - Slinkov, Grigorii; Becker, Steven; Englund, Dirk; Stiller, Birgit (2023 International Conference on Photonics in Switching and Computing, PSC 2023, 2023)
We experimentally demonstrate an in-fiber optoacoustic nonlinear activation function based on stimulated Brillouin scattering. The activation function can be tuned all-optically and shows an input-output behaviour of a LeakyReLU, Sigmoid, and quadratic function. Our scheme is coherent and frequency selective, which is suitable for operation in multi-frequency neural networks. In addition, the optoacoustic activation function can amplify its input signal, allowing to compensate on-the-fly for optical losses during propagation.
CRIS-Team Scopus Importer:2023-12-15
Keywords: neuromorphic computing; nonlinear optics; Optical neural networks; stimulated Brillouin scattering

Photonic crystal fibers for generating three-photon states - Chekhova, Maria; Cavanna, Andrea; Taheri, Michael; Okoth, C.; Jiang, X.; Joly, Nicolas; Russell, Philip St. John (2017 Conference on Lasers and Electro-Optics, CLEO 2017 - Proceedings, 2017)
Direct decay of pump photons into triplets is an interesting but not-yet-realized nonlinear effect. We are exploring two approaches using photonic crystal fibers: a gas-filled hollow-core PCF and the recently designed hybrid solid-core PCF.
CRIS-Team Scopus Importer:2023-03-27

Photonic crystal fibres for chemical sensing and photochemistry - Cubillas, Ana Maria; Unterkofler, Sarah; Euser, Tijmen G.; Etzold, Bastian; Jones, Anita C.; Sadler, Peter J.; Wasserscheid, Peter; Russell, Philip St. John (Chemical Society Reviews, 2013)
In this review, we introduce photonic crystal fibre as a novel optofluidic microdevice that can be employed as both a versatile chemical sensor and a highly efficient microreactor.We demonstrate that it provides an excellent platform in which light and chemical samples can strongly interact for quantitative spectroscopic analysis or photoactivation purposes. The use of photonic crystal fibre in photochemistry and sensing is discussed and recent results on gas and liquid sensing as well as on photochemical and catalytic reactions are reviewed. These developments demonstrate that the tight light confinement, enhanced light-matter interaction and reduced sample volume offered by photonic crystal fibre make it useful in a wide range of chemical applications.

Photon-number noise of spectrally filtered optical solitons - Leuchs, Gerd; et al. (New trend in optical soliton transmission systems, 1998)
UnivIS-Import:2015-04-20:Pub.1998.nat.dphy.optik.1optik.photon

Photon-number squeezed solitons from an asymmetric fiber-optic Sagnac interferometer - Leuchs, Gerd; et al. (Physical Review Letters, 1998)
Direct photon-number squeezing is demonstrated, for the first time to our knowledge, in a nonlinear fiber-optic interferometer. Launching 126-fs solitons into a highly asymmetric Sagnac loop, the maximum photocurrent noise reduction was 3.9 ± 0.2 dB below shot noise, corresponding to 6.0 ± 0.9 dB, when corrected for linear losses. The loop is a model system for squeezing generated by the interference of two pulses after nonlinear propagation through a fiber.
UnivIS-Import:2015-03-05:Pub.1998.nat.dphy.optik.1optik.photon_6

Photon Number Squeezing of Spectrally Filtered Sub-Picosecond Optical Solitons - Leuchs, Gerd; et al. (EPL - Europhysics Letters, 1997)
Photon number squeezing of spectrally filtered optical solitons has been observed in the sub-picosecond regime, where the Raman effect changes the internal quantum structure of each pulse. 160 fs pulses were propagated down a 10 m optical fibre of anomalous group velocity dispersion. At energies below the soliton energy subsequent spectral filtering with an optical band-pass squeezed the directly detected photocurrent fluctuations to 3.2 ± 0.1 dB (52%) below the shot-noise limit. This implies 4.5 dB (65%) of soliton photon number squeezing, if detection losses are taken into account. Using a spectral edge filter the spectral components of the pulses are shown to contribute asymmetrically to the squeezing due to stimulated Raman scattering.
UnivIS-Import:2015-03-05:Pub.1997.nat.dphy.optik.1optik.photon

Photon pairs bi-directionally emitted from a resonant metasurface - Son, Changjin; Sultanov, Vitaliy; Santiago Cruz, Tomás; Anthur, Aravind P. P.; Zhang, Haizhong; Paniagua-Dominguez, Ramon; Krivitsky, Leonid; Kuznetsov, Arseniy I. I.; Chekhova, Maria (Nanoscale, 2023)
Metasurfaces are artificially structured surfaces able to control the properties of light at subwavelength scales. While, initially, they have been proposed as means to control classical optical fields, they are now emerging as nanoscale sources of quantum light, in particular of entangled photons with versatile properties. Geometric resonances in metasurfaces have been recently used to engineer the frequency spectrum of entangled photons, but the emission directivity was so far less studied. Here, we generate photon pairs via spontaneous parametric down conversion from a metasurface supporting a quasi-bound state in the continuum (BIC) leading to remarkable emission directivities. The pair generation rate is enhanced 67 times compared to the case of an unpatterned film of the same thickness and material. At the wavelength of the quasi-BIC resonance, photons are mostly emitted backwards, while their partners, spectrally detuned by only 8 nm, are emitted forwards. This behavior demonstrates fine spectral splitting of entangled photons and their bi-directional emission, never before observed in nanoscale sources. We expect this work to be a starting point for the efficient demultiplexing of photons in nanoscale quantum optics.
CRIS-Team WoS Importer:2023-02-10

Photon Pairs from Resonant Metasurfaces - Santiago-Cruz, Tomás; Fedotova, Anna; Sultanov, Vitaliy; Weissflog, Maximilian A.; Arslan, Dennis; Younesi, Mohammadreza; Pertsch, Thomas; Staude, Isabelle; Setzpfandt, Frank; Chekhova, Maria (Nano Letters, 2021)
All-dielectric optical metasurfaces are a workhorse in nano-optics, because of both their ability to manipulate light in different degrees of freedom and their excellent performance at light frequency conversion. Here, we demonstrate first-time generation of photon pairs via spontaneous parametric-down conversion in lithium niobate quantum optical metasurfaces with electric and magnetic Mie-like resonances at various wavelengths. By engineering the quantum optical metasurface, we tailor the photon-pair spectrum in a controlled way. Within a narrow bandwidth around the resonance, the rate of pair production is enhanced up to 2 orders of magnitude, compared to an unpatterned film of the same thickness and material. These results enable flat-optics sources of entangled photons - a new promising platform for quantum optics experiments.
CRIS-Team Scopus Importer:2021-06-04
Keywords: Mie-type resonances; nonlinear metasurfaces; photon-pair generation; quantum optics; spontaneous parametric down-conversion

Photon Propagation in a Discrete Fiber Network: An Interplay of Coherence and Losses - Regensburger, Alois; Bersch, Christoph; Hinrichs, Benjamin; Onishchukov, Georgy; Schreiber, Andreas; Silberhorn, Christine; Peschel, Ulf (Physical Review Letters, 2011)
We study light propagation in a photonic system that shows stepwise evolution in a discretized environment. It resembles a discrete-time version of photonic waveguide arrays or quantum walks. By introducing controlled photon losses to our experimental setup, we observe unexpected effects like subexponential energy decay and formation of complex fractal patterns. This demonstrates that the interplay of linear losses, discreteness and energy gradients leads to genuinely new coherent phenomena in classical and quantum optical experiments. Moreover, the influence of decoherence is investigated.
EAM Import::2019-03-12

Photon-Qubit Entanglement and Hong-Ou-Mandel Interference at Microwave Frequencies - Eichler, Christopher (Workshop on Frontier between atomic and solid state physics, 2013)
Keywords: wwwqudev

Physikalische Grenzen der Formerfassung mit Licht - Häusler, Gerd; Leuchs, Gerd (Physikalische Blätter, 1997)
UnivIS-Import:2015-03-05:Pub.1997.nat.dphy.optik.1optik.physik

Picosecond acoustic dynamics in stimulated Brillouin scattering - Piotrowski, Johannes; Schmidt, Mikolaj K.; Stiller, Birgit; Poulton, Christopher G.; Steel, Michael J. (Optics Letters, 2021)
Recent experiments demonstrating storage of optical pulses in acoustic phonons via stimulated Brillouin scattering raise questions about the spectral and temporal capacities of such protocols and the limitations of the theoretical frameworks routinely used to describe them. We consider the dynamics of photon-phonon scattering induced by optical pulses with temporal widths comparable to the period of acoustic oscillations. We revisit the widely adopted classical formalism of coupled modes and demonstrate its breakdown. We use a simple extension to the formulation and find potentially measurable consequences in the dynamics of Brillouin experiments involving ultrashort pulses.
CRIS-Team Scopus Importer:2021-06-25

Plasmonic carbon nanohybrids from laser-induced deposition: controlled synthesis and SERS properties - Povolotckaia, Anastasia; Pankin, Dmitrii; Petrov, Yuriy; Vasileva, Anna; Kolesnikov, Ilya; Sarau, George; Christiansen, Silke; Leuchs, Gerd; Manshina, Alina (Journal of Materials Science, 2019)
A novel single-step, laser-induced and solution-based process is presented for synthesizing complex hybrid metal/carbon nanostructures. The process relies on simply illuminating the interface between a substrate and a liquid solution of the supramolecular complex [Au13Ag12(C2Ph)(20)(PPh2(C6H4)(3)PPh2)(3)][PF6](5) (hereinafter abbreviated as SMC) with an unfocussed He-Cd laser having a wavelength of 325nm and an intensity of I=0.5W/cm(2). The process results in hybrid nanostructures of well-controlled morphology: nanoparticles (NP) and 2D flakes, which may also grow jointly to form 3D morphologically complex multipetal flower-like' structures. At the atomic scale, the obtained metamaterials are complex in composition and structure, i.e., they contain bimetallic Au-Ag nanoclusters of diameter 3-5nm incorporated inside a carbonaceous matrix. This matrix can be amorphous or crystalline, and the details of the compositional outcome can be controlled and steered by the laser deposition parameters. Au-Ag nanoclusters show plasmonic behavior including the enhancement of electromagnetic fields of visible light. This leads to the enhancement of Raman scattering by the Au-Ag nanoparticle ensemble within the carbonaceous matrix. This enables a 3D architecture for stimulating surface-enhanced Raman scattering (SERS).
CRIS-Team WoS Importer:2019-04-04

Plasmonic excitations in metallic nanoparticles: Resonances, dispersion characteristics and near-field patterns - Tatartschuk, Eugen; Shamonina, Ekaterina; Solymar, Laszlo (Optics Express, 2009)
Metamaterials acquire their functionality from the structuring of the small building blocks, ``artificial atoms''. Our paper provides a study of the resonant behaviour for a variety of metallic nanoparticles in the region of hundreds of THz. Resonant modes for nanorods of rectangular cross section are investigated numerically for different types of excitation and the set of resonant frequencies (fundamental and higher order) are determined for rods of various length. From that the dispersion relationship for surface plasmon-polaritons propagating along the rod is deduced. We analyse resonant-mode near-field distribution of the electric field, including the field lines, to emphasise the underlying physics. Resonant frequencies are also found and field distributions analysed when the rods are combined to form particles of L, U and O shapes. The similarities and differences between those particles, both in the values and in the number of resonances, are discussed. The results of this study may aid the design of nanostructured metamaterials with required properties in the IR and optical domain.
EAM Import::2019-03-12

Point spread function in interferometric scattering microscopy (iSCAT). Part I: aberrations in defocusing and axial localization - Mahmoodabadi, Reza Gholami; Taylor, Richard W.; Kaller, Martin; Spindler, Susann; Mazaheri, Mahdi; Kasaian, Kiarash; Sandoghdar, Vahid (Optics Express, 2020)
Interferometric scattering (iSCAT) microscopy is an emerging label-free technique optimized for the sensitive detection of nano-matter. Previous iSCAT studies have approximated the point spread function in iSCAT by a Gaussian intensity distribution. However, recent efforts to track the mobility of nanoparticles in challenging speckle environments and over extended axial ranges has necessitated a quantitative description of the interferometric point spread function (iPSF). We present a robust vectorial diffraction model for the iPSF in tandem with experimental measurements and rigorous FDTD simulations. We examine the iPSF under various imaging scenarios to understand how aberrations due to the experimental configuration encode information about the nanoparticle. We show that the lateral shape of the iPSF can be used to achieve nanometric three-dimensional localization over an extended axial range on the order of 10 µm either by means of a fit to an analytical model or calibration-free unsupervised machine learning. Our results have immediate implications for three-dimensional single particle tracking in complex scattering media.
CRIS-Team Scopus Importer:2020-09-18

Polarisations- und phasenschiebende Interferometrie für die simultane Vermessung der Phasenfront und der Absorption / des Dichroismus eines Objekts - Rothau, Sergej; Lindlein, Norbert (119. Jahrestagung der DGaO, 2018)

Polarisations- und phasenschiebende Interferometrie für die simultane Vermessung der Phasenfront und der Doppelbrechung eines Objekts - Rothau, Sergej; Mantel, Klaus; Lindlein, Norbert (118. Jahrestagung der DGaO, 2017)

Polarization and phase shifting interferometry - Rothau, Sergej; Mantel, Klaus; Lindlein, Norbert (Proc. SPIE 10329, 2017)
This publication presents a novel interferometric method for the simultaneous measurement of the phase andstate of polarization of a light wave with arbitrary, in particular locally varying elliptical polarization. The mea-surement strategy is based on variations of the reference wave concerning phase and polarization and processingthe interference patterns so obtained. With this method, that is very similar to the classical phase shiftinginterferometry, a complete analysis of spatially variant states of polarization and their phase fronts can be donein one measurement cycle. Furthermore, a direct analysis of specimens under test regarding birefringence andthe impact on the phase of the incoming light can be realized. The theoretical description of the investigatedmethods and their experimental implementation are presente

Polarization and phase shifting interferometry - Rothau, Sergej; Mantel, Klaus; Lindlein, Norbert (Conference on Lasers and Electro-Optics, 2019)
A novel interferometric approach for a full-field and simultaneous measurement of the phase and the polarization state of a light wave is introduced. The same procedure can be used for simultaneous analysis of the phase transmission and the polarization properties of a specimen.
Keywords: Light beams; Light fields; Phase measurement; Phase shifting interferometry; Polarization; Transmission coefficient

Polarization and phase-shifting interferometry for arbitrary, locally varying polarization states - Rothau, Sergej; Kellermann, Christine; Mayer, Simon; Mantel, Klaus Peter; Lindlein, Norbert (Applied Optics, 2017)
This publication presents what we believe is a novel interferometric method for the simultaneous measurement of the phase and state of polarization of a light wave with arbitrary polarization; in particular, it can be varying elliptical. The measurement strategy is based on variations of the reference wave, concerning phase and polarization and processing the interference patterns so obtained. With this method, which is very similar to classical phase-shifting interferometry, the general analysis of spatially variant states of polarization and their phase fronts can be done in one measurement cycle. Furthermore, the analysis of different optical elements regarding the impact on the polarization and phase of the incoming light can be realized. After the theoretical description of the method and the mathematical discussion of different algorithms, the realized measurement setup is presented. Afterward, the accuracy of the method is discussed.

Polarization and phase shifting interferometry for the simultaneous measurement of phase and polarization. - Rothau, Sergej; Lindlein, Norbert (2016)

Polarization and phase shifting interferometry for the simultaneous measurement of the phase and polarization - Rothau, Sergej; Lindlein, Norbert (117. Annual Meeting of the DGaO, 2016)

Polarization correlations in quantum optics - Sánchez-Soto, L. L.; Klimov, A. B.; Björk, G.; Söderholm, J.; Andersen, U. L.; Marquardt, Christoph; Leuchs, Gerd (Optics InfoBase Conference Papers, 2011)
The standard degree of polarization involves exclusively first-order moments of the Stokes variables. This may be sufficient for most classical problems, but for quantum fields higher-order correlations are crucial. We claim that a complete polarization characterization must involve a whole hierarchy of polarization degrees constructed order by order, as it happens in coherence theory. We present here a second-order degree and determine it experimentally. ©2011 Optical Society of America.
CRIS-Team Scopus Importer:2022-06-05

Polarization-dependent effects on phase singularities in the vicinity of sub-lambda structures - Leuchs, Gerd; et al. (SPIE j, 2002)
UnivIS-Import:2015-03-09:Pub.2002.nat.dphy.optik.1optik.polari_0

Polarization-Encoded Colocalization Microscopy at Cryogenic Temperatures - Böning, Daniel; Wieser, Franz Ferdinand; Sandoghdar, Vahid (ACS Photonics, 2021)
Super-resolution localization microscopy is based on determining the positions of individual fluorescent markers in a sample. The major challenge in reaching an ever higher localization precision lies in the limited number of collected photons from single emitters. To tackle this issue, it has been shown that one can exploit the increased photostability at low temperatures, reaching localization precisions in the subnanometer range. Another crucial ingredient of single-molecule super-resolution imaging is the ability to activate an individual emitter within a diffraction-limited spot. Here, we report on the photoblinking behavior of organic dyes at low temperature and elaborate on the limitations of this ubiquitous phenomenon for selecting single molecules. We then show that recording the emission polarization not only provides access to the molecular orientation, but it also facilitates the assignment of photons to individual blinking molecules. Furthermore, we employ periodical modulation of the excitation polarization as a robust method to effectively switch fluorophores. We benchmark each approach by resolving two emitters on different DNA origami structures.
CRIS-Team Scopus Importer:2021-02-12
Keywords: cryogenic light microscopy; DNA origami; polarization; single-molecule localization microscopy

Polarization features of optically pumped CdS nanowire lasers - Roeder, Robert; Ploss, Daniel; Kriesch, Arian; Buschlinger, Robert; Geburt, Sebastian; Peschel, Ulf; Ronning, Carsten (Journal of Physics D-Applied Physics, 2014)
High quality CdS nanowires suspended in air were optically pumped both below and above the lasing threshold. The polarization of the pump laser was varied while emission out of the end facet of the nanowire was monitored in a `head-on' measurement geometry. Highest pump-efficiency and most efficient absorption of the pump radiation are demonstrated for an incident electric field being polarized parallel to the nanowire axis. This polarization dependence, which was observed both above the lasing threshold and in the regime of amplified spontaneous emission, is caused by an enhanced absorption for parallel polarized optical pumping. Measured Stokes parameters of the nanowire emission reveal that due to the onset of lasing the degree of polarization rapidly increases from approximately 15 to 85%. Both Stokes parameters and degree of polarization of the nanowire lasing emission are independent of the excitation polarization. The transversal lasing mode is therefore not notably affected by the polarization of the pumping beam, although the supply with optical gain is significantly enhanced for an excitation polarization parallel to the nanowire axis.
EAM Import::2019-03-08

Polarization noise induced by photon-phonon interaction in hollow-core photonic crystal fibres - Zhong, W.; Heim, B.; Elser, D.; Marquardt, Christoph; Leuchs, Gerd (2011 Conference on Lasers and Electro-Optics Europe and 12th European Quantum Electronics Conference, CLEO EUROPE/EQEC 2011, 2011)
Guided acoustic wave Brillouin scattering (GAWBS), a weak forward scattering that stems from the interaction of light with thermally excited transverse phonons, has been studied in both standard fibres [1] and photonic crystal fibres [2, 3]. The acoustic phonon vibrations modulate the stress distribution in the silica fibre core, thus modulating the refractive index and inducing polarization and phase noise in the light field. © 2011 IEEE.
CRIS-Team Scopus Importer:2022-06-05

Polarization optimized 4-π geometries for microscopy - Lindlein, Norbert; et al. (Frontiers in Optics, FiO 2007, 2007)
A smaller focal spot can be obtained by choosing a tailored polarization, e.g. radial polarization in the case rotationally symmetric high numerical aperture focusing. The same polarization mode maximizes the coupling to an atom when using the correct 4π geometry for transforming the incident light field. © 2007 Optical Society of America.

Polarization optimized focusing of light and coupling to sub-wavelength antennae - Leuchs, Gerd; et al. (Nanophotonics, 2004)
UnivIS-Import:2015-04-20:Pub.2004.nat.dphy.optik.1optik.polari

Polarization-Selective Out-Coupling of Whispering-Gallery Modes - Sedlmeir, Florian; Foreman, Matthew R.; Vogl, Ulrich; Zeltner, Richard; Schunk, Gerhard; Strekalov, Dmitry V.; Marquardt, Christoph; Leuchs, Gerd; Schwefel, Harald G. L. (Physical Review Applied, 2017)
Whispering-gallery mode (WGM) resonators are an important platform for linear, nonlinear, and quantum optical experiments. In such experiments, independent control of in-coupling and out-coupling rates to different modes can lead to higher conversion efficiencies and greater flexibility in the generation of nonclassical states based on parametric down-conversion. In this work, we introduce a scheme that enables selective out-coupling of WGMs belonging to a specific polarization family, while the orthogonally polarized modes remain largely unperturbed. Our technique utilizes material birefringence in both the resonator and the coupler such that a negative (positive) birefringence allows for polarization-selective coupling to TE (TM) WGMs. We formulate a refined coupling condition suitable for describing the case where the refractive indices of the resonator and the coupler are almost the same, from which we derive a criterion for polarization-selective coupling. Finally, we experimentally demonstrate our proposed method using a lithium niobate disk resonator coupled to a lithium niobate prism, where we show a 22-dB suppression of coupling to TM modes relative to TE modes.
CRIS-Team Scopus Importer:2022-06-05

Polarization sensitive lateral photoconductivity in GaAs/AlGaAs quantum well based structures on low-temperature grown GaAs(001) - Arora, Ashish; Gosh, Sandip; Arora, Brij Mohan; Malzer, Stefan; Döhler, Gottfried (Applied Physics Letters, 2010)
Polarization-resolved lateral-photoconductivity measurements are reported on device structures made of GaAs/ Al Ga As quantum wells sandwiched between low-temperature grown GaAs(001) layers. The mesa device structures have long length (3 mmy) and narrow width (10 and 20 μmx) in the (001) plane. For light incident along [001], the ground state light-hole exciton transition is much stronger for light polarization Ex, compared to Ey. The heavy-hole exciton transition shows a weaker polarization anisotropy of opposite sign, being stronger for Ey. Through calculations based on the Bir-Pikus Hamiltonian, the observed in-plane optical polarization anisotropy is shown to arise from valence band mixing induced by anisotropic strain in the plane of quantum wells. © 2010 American Institute of Physics.

Polarization Squeezing and Continuous Variable Polarization Entanglement - Leuchs, Gerd; et al. (Physical Review A, 2002)
Polarization squeezing and continuous-variable polarization entanglement of light was studied. To study this concept, the properties of Stokes parameters and Poincare sphere were studied. For a range of simple polarization states, the general features of the Stokes operators were illustrated by evaluating their means and variances. It was shown that the Stokes parameters can be measured by the use of linear optical elements and direct detection schemes that are sensitive to the quantum correlations in the two polarization components of the light.
UnivIS-Import:2015-03-09:Pub.2002.nat.dphy.optik.1optik.polari

Polarization squeezing of intense pulses with a fiber Sagnac interferometer - Leuchs, Gerd; et al. (Physical Review A, 2003)
Quantum information and communication are important fields for the future. Due to the ease of detection of the Stokes operators, polarization squeezing will play an important role in the development of these fields, not least as a basis for polarization entanglement. This paper investigated polarization squeezing of intense pulses, using amplitude squeezed pulses generated by the Kerr nonlinearity of a glass fiber.
UnivIS-Import:2015-03-09:Pub.2003.nat.dphy.optik.1optik.polari

Polarization squeezing with photonic crystal fibers - Milanovic, Josip; Heersink, Joel; Marquardt, Christoph; Huck, A.; Andersen, Ulrik Lund; Leuchs, Gerd (Laser Physics, 2007)
UnivIS-Import:2015-03-09:Pub.2007.nat.dphy.optik.1optik.polari

Polarization-Tailored Raman Frequency Conversion in Chiral Gas-Filled Hollow-Core Photonic Crystal Fibers - Davtyan, S.; Novoa, D.; Chen, Y.; Frosz, M. H.; Russell, Philip St. John (Physical Review Letters, 2019)
Broadband-tunable sources of circularly polarized light are crucial in fields such as laser science, biomedicine, and spectroscopy. Conventional sources rely on nonlinear wavelength conversion and polarization control using standard optical components and are limited by the availability of suitably transparent crystals and glasses. Although a gas-filled hollow-core photonic crystal fiber provides pressure-tunable dispersion, long well-controlled optical path lengths, and high Raman conversion efficiency, it is unable to preserve a circular polarization state, typically exhibiting weak linear birefringence. Here we report a revolutionary approach based on a helically twisted hollow-core photonic crystal fiber, which displays circular birefringence, thus robustly maintaining a circular polarization state against external perturbations. This makes it possible to generate pure circularly polarized Stokes and anti-Stokes signals by rotational Raman scattering in hydrogen. The polarization state of the frequency-shifted Raman bands can be continuously varied by tuning the gas pressure in the vicinity of the gain-suppression point. The results pave the way to a new generation of compact and efficient fiber-based sources of broadband light with a fully controllable polarization state.
CRIS-Team WoS Importer:2019-04-30

Polychromatic Maximum Likelihood Reconstruction for Talbot-Lau X-ray Tomography - Schiffers, Florian; Käppler, Sebastian; Pelzer, Georg; Wolf, Andreas; Maier, Andreas; Anton, Gisela; Riess, Christian (International Conference on Fully Three-Dimensional Image Reconstruction in Radiology and Nuclear Medicine (Fully3D), 2017)

Post-recombination effects in confined gases photoionized at megahertz repetition rates - Koehler, J. R.; Kottig, F.; Schade, Daniel; Russell, Philip St. John; Tani, F. (Optics Express, 2021)
Recombination-driven acoustic pulses and heating in a photoionized gas transiently alter its refractive index. Slow thermal dissipation can cause substantial heat accumulation and impair the performance and stability of gas-based laser systems operating at strong-field intensities and megahertz repetition rates. Here we study this effect by probing the pulse-by-pulse buildup of refractive index changes in gases spatially confined inside a capillary. A high-power repetition-rate-tunable femtosecond laser photoionizes the gas at its free-space focus, while a transverse-propagating probe laser interferometrically monitors the resulting time-dependent changes in refractive index. The system allows convenient exploration of the nonlinear regimes used to temporally compress pulses with durations in the similar to 30 to similar to 300 fs range. We observe thermal gas-density depressions, milliseconds in duration, that saturate to a level that depends on the peak intensity and repetition rate of the pulses, in good agreement with numerical modelling. The dynamics are independently confirmed by measuring the mean speed-of-sound across the capillary core, allowing us to infer that the temperature in the gas can exceed 1000 K. Finally, we explore several strategies for mitigating these effects and improving the stability of gas-based high-power laser systems at high repetition rates. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
CRIS-Team WoS Importer:2021-03-19

Practical continuous variable QKD in fiber and free space systems - Marquardt, Christoph (Frontiers in Optics 2016, 2016)
I will review recent activities in continuous variable QKD that aims for the deployment of QKD equipment compatible with current telecom standards and research in satellite QKD that will make it possible to bridge long distances.<br

Practical limitations of Talbot imaging with microlens arrays - Lindlein, Norbert; et al. (Journal of Optics A: Pure and Applied Optics, 1997)
The Talbot effect which also appears for the foci of microlens arrays can, in principle, be used for array illuminators. In particular, the multiplication of the foci in the fractional Talbot planes seems to be promising. Certainly, in practice there are three effects which limit the application of the fractional Talbot effect for microlens arrays. Theoretical, numerical and experimental results are given to demonstrate these limitations. © 1997 IOP Publishing Ltd.
UnivIS-Import:2015-03-05:Pub.1997.nat.dphy.optik.1optik.practi

Practical limits of an optimized quantum receiver - Marquardt, Christoph; Müller, Christian R.; Leuchs, Gerd (Optics InfoBase Conference Papers, 2014)
We present a quantum receiver for the discrimination of quadrature phase-shift keyed signals that approaches the Helstrom bound for any signal power and discuss the influence of practical limitations. © 2014 Optical Society of America.
CRIS-Team Scopus Importer:2022-06-05

Practical notes on designing and analysing thick holographic optical elements - Lindlein, Norbert; Schwider, Johannes (Journal of Optics A: Pure and Applied Optics, 1992)
Equations for tracing rays through (aspheric) holographic optical elements (HOE) are reviewed, and, in addition, the diffraction efficiency of a thick HOE is taken into account. Expressions for calculating the phase functions of aspheric recording wave fronts of a thick HOE in the presence of a wavelength shift are given. A simple least squares fitting algorithm is used to compute analytic expressions of these phase functions. Finally, a method to calculate a focus of rays is described.

Precise balancing of viscous and radiation forces on a particle in liquid-filled photonic bandgap fiber - Euser, T. G.; Garbos, M. K.; Chen, J. S. Y.; Russell, Philip St. John (Optics Letters, 2009)
A great challenge in microfluidics is the precise control of laser radiation forces acting on single particles or cells, while allowing monitoring of their optical and chemical properties. We show that, in the liquid-filled hollow core of a single-mode photonic crystal fiber, a micrometer-sized particle can be held stably against a fluidic counterflow using radiation pressure and can be moved to and fro (over tens of centimeters) by ramping the laser power up and down. Accurate studies of the microfluidic drag forces become possible, because the particle is trapped in the center of the single guided optical mode, resulting in highly reproducible radiation forces. The counterflowing liquid can be loaded with sequences of chemicals in precisely controlled concentrations and doses, making possible studies of single particles, vesicles, or cells.
EAM Import::2019-03-08

Precision estimation of source dimensions from higher-order intensity correlations - Pearce, M. E.; Mehringer, Thomas; von Zanthier, Joachim; Kok, P. (Physical Review A, 2015)
An important topic of interest in imaging is the construction of protocols that are not diffraction limited. This can be achieved in a variety of ways, including classical superresolution techniques or quantum entanglement-based protocols. Here, we consider superresolving imaging in the far field using higher-order intensity correlations. We show that third-and fourth-order correlations can improve upon the first-and second-order correlations that are traditionally used in classical optics and Hanbury Brown-Twiss-type experiments. The improvement is achieved entirely by post-processing of the data. As a demonstrator, we simulate the far field intensity distribution of a circular aperture that emits thermal light and use maximum likelihood estimation to determine the radius of the aperture. We compare the achieved precision to the Cramer-Rao lower bound and find that the variance of measurements for the third-and fourth-order correlation functions are indeed closer to the Cramer-Rao bound than that of the second-order correlation function. The method presented here is general, and can be used for all kinds of incoherent emitters, geometries, and types of nois

Precision in Length - Leuchs, Gerd (Laser Physics at the Limits, 2002)
UnivIS-Import:2015-04-20:Pub.2002.nat.dphy.optik.1optik.precis

Precision single-particle localization using radial variance transform - Kashkanova, Anna D.; Shkarin, Alexey B.; Mahmoodabadi, Reza Gholami; Blessing, Martin; Tuna, Yazgan; Gemeinhardt, Andre; Sandoghdar, Vahid (Optics Express, 2021)
We introduce an image transform designed to highlight features with high degree of radial symmetry for identification and subpixel localization of particles in microscopy images. The transform is based on analyzing pixel value variations in radial and angular directions. We compare the subpixel localization performance of this algorithm to other common methods based on radial or mirror symmetry (such as fast radial symmetry transform, orientation alignment transform, XCorr, and quadrant interpolation), using both synthetic and experimentally obtained data. We find that in all cases it achieves the same or lower localization error, frequently reaching the theoretical limit.
CRIS-Team Scopus Importer:2021-04-30

Pressure-driven collective growth mechanism of planar cell colonies. - Metzner, Claus; Lange, Janina; Krauß, Patrick; Wunderling, Nico; Übelacker, Julian; Martin, Florian; Fabry, Ben (Journal of Physics D-Applied Physics, 2018)

Pressure-driven collective growth mechanism of planar cell colonies. - Metzner, Claus; Lange, Janina; Krauß, Patrick; Wunderling, Nico; Übelacker, Julian; Martin, Florian; Fabry, Ben (Journal of Physics D: Applied Physics, 2018)
The growth of cell colonies is determined by the migration and proliferation of the individual cells. This is often modeled with the Fisher-Kolmogorov (FK) equation, which assumes that cells diffuse independently from each other, but stop to proliferate when their density reaches a critial limit. However, when using measured, cell-line specific parameters, we find that the FK equation drastically underestimates the experimentally observed increase of colony radius with time. Moreover, cells in real colonies migrate radially outward with superdiffusive trajectories, in contrast to the assumption of random diffusion. We demonstrate that both dicrepancies can be resolved by assuming that cells in dense colonies are driven apart by repulsive, pressure-like forces. Using this model of proliferating repelling particles (PRP), we find that colony growth exhibits different dynamical regimes, depending on the ratio between a pressure-related equilibrium cell density and the critial density of proliferation arrest.
EVALuna2:210450

Pressure-tuned phase-matched generation of non-classical light in microstructured fibre - Joly, Nicolas; Hammer, Jonas; Pennetta, R.; Cavanna, A.; Chekhova, Maria (23RD OPTO-ELECTRONICS AND COMMUNICATIONS CONFERENCE (OECC2018), 2018)
CRIS-Team WoS Importer:2019-08-13

Previous Record Record 8 of 11 Next Record Record from Web of Science® On the calibration of diffractive nulls for transmission tests of aspheric components - Schwider, Johannes; Lindlein, Norbert; Mantel, Klaus Peter; Harder, Irina (Optics Communications, 2007)
UnivIS-Import:2015-04-14:Pub.2007.nat.dphy.optik.1optik.previo

Prime number decomposition using the Talbot effect - Pelka, Karl; Graf, Jasmin; Mehringer, Thomas; von Zanthier, Joachim (Optics Express, 2018)
We report on prime number decomposition by use of the Talbot effect, a well-known phenomenon in classical near field optics whose description is closely related to Gauss sums. The latter are a mathematical tool from number theory used to analyze the properties of prime numbers as well as to decompose composite numbers into their prime factors. We employ the well-established connection between the Talbot effect and Gauss sums to implement prime number decompositions with a novel approach, making use of the longitudinal intensity profile of the Talbot carpet. The new algorithm is experimentally verified and the limits of the approach are discussed. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Probabilistic amplification and cloning of phase-covariant coherent states - Müller, C. R.; Wittmann, C.; Marek, P.; Filip, R.; Usuga, M. A.; Marquardt, Christoph; Andersen, U. L.; Leuchs, Gerd (Optics InfoBase Conference Papers, 2011)
CRIS-Team Scopus Importer:2022-06-05

Probabilistic cloning of coherent states without a phase reference - Mueller, Christian R.; Wittmann, Christoffer; Marek, Petr; Filip, Radim; Marquardt, Christoph; Leuchs, Gerd; Andersen, Ulrik L. (Physical Review A - Atomic, Molecular, and Optical Physics, 2012)
We present a probabilistic cloning scheme operating independently of any phase reference. The scheme is based solely on a phase-randomized displacement and photon counting, omitting the need for nonclassical resources and nonlinear materials. In an experimental implementation, we employ the scheme to clone coherent states from a phase covariant alphabet and demonstrate that the cloner is capable of outperforming the hitherto best-performing deterministic scheme. An analysis of the covariances between the output states shows that uncorrelated clones can be approached asymptotically. This simultaneously demonstrates how the effect of loss on coherent states can be compensated via noiseless preamplification. © 2012 American Physical Society.
CRIS-Team Scopus Importer:2022-06-05

Probing colloidal interfaces by angle-resolved second harmonic light scattering - Schürer, Benedikt; Wunderlich, Sarina; Sauerbeck, Christian; Peschel, Ulf; Peukert, Wolfgang (Physical Review B, 2010)
We report angle-resolved second harmonic light scattering from bare colloidal particles in water. A nonlinear Mie model is used to quantitatively analyze the nonresonant second harmonic (SH) scattering profiles and to determine the elements of the local second-order surface susceptibility. The SH signal is attributed to oriented and electrically polarized water molecules at the charged particle interface. The results show how angle-resolved SH light scattering can be applied to probe not only resonant excited dye molecules but also nonresonant molecules such as water at the interface of colloidal particles.

Probing guided modes in a monolayer colloidal crystal on a flat metal film - Romanov, Sergei G.; Vogel, Nicolas; Bley, Karina; Landfester, Katharina; Weiss, Clemens K.; Orlov, Sergej; Korovin, Alexander V.; Chuiko, Gennady P.; Regensburger, Alois; Romanova, Alexandra; Kriesch, Arian; Peschel, Ulf (Physical Review B, 2012)
Two-dimensional slab hybrid metal-dielectric photonic crystals, which are prepared by assembling polymer colloidal spheres into closely packed monolayers of hexagonal symmetry on a gold-coated glass substrate, show an improved confinement of light compared with a colloidal monolayer on a glass substrate. We demonstrated that the optical response of such hybrid crystals consists of diffractively coupled waveguiding modes, Fabry–Perot resonances, and Mie resonances. Correspondingly, two major mechanisms, namely, band transport and hopping of localized excitations, participate in the in-plane light transport in such hybrid crystals.

Probing the quantum properties of microwave radiation emitted from superconducting circuits. - Eichler, Christopher (Hannover, Institut für Theoretische Physik, 2013)
Keywords: wwwqudev

Processing Range Data for Reverse Engineering and Virtual Reality - Häusler, Gerd; et al. (Proceedings of Third International Conference on 3-DDigital Imaging and Modeling, 2001)
UnivIS-Import:2015-04-16:Pub.2001.nat.dphy.optik.1optik.proces

Production and control of refractive and diffractive microlenses - Lindlein, Norbert; et al. (Proceedings of the 4th International Conference on Holographic Systems, Components and Applications, 1993)
Here we will discuss two examples of microlenses where the generation process and the interferometric control are strongly interwoven. We developed an evaluation software under windows.

Production of isolated giant unilamellar vesicles under high salt concentrations - Stein, Hannah; Spindler, Susann; Bonakdar, Navid; Wang, Chun; Sandoghdar, Vahid (Frontiers in Physiology, 2017)
The cell membrane forms a dynamic and complex barrier between the living cell and its environment. However, its in vivo studies are difficult because it consists of a high variety of lipids and proteins and is continuously reorganized by the cell. Therefore, membrane model systems with precisely controlled composition are used to investigate fundamental interactions of membrane components under well-defined conditions. Giant unilamellar vesicles (GUVs) offer a powerful model system for the cell membrane, but many previous studies have been performed in unphysiologically low ionic strength solutions which might lead to altered membrane properties, protein stability and lipid-protein interaction. In the present work, we give an overview of the existing methods for GUV production and present our efforts on forming single, free floating vesicles up to several tens of μm in diameter and at high yield in various buffer solutions with physiological ionic strength and pH.
CRIS-Team Scopus Importer:2023-03-27
Keywords: Double emulsion; Electroformation; Giant unilamellar vesicle; Lipid membrane; Microfluidic jetting; Micropipette aspiration; Model membrane system; Swelling

Progress toward third-order parametric down-conversion in optical fibers - Cavanna, Andrea; Hammer, Jonas; Okoth, Cameron; Ortiz-Ricardo, Erasto; Cruz-Ramirez, Hector; Garay-Palmett, Karina; U'Ren, Alfred B.; Frosz, Michael H.; Jiang, Xin; Joly, Nicolas; Chekhova, Maria (Physical Review A, 2020)
Optical fibers have been considered an optimal platform for third-order parametric down-conversion since they can potentially overcome the weak third-order nonlinearity by their long interaction length. Here we present, in the first part, a theoretical derivation for the conversion rate both in the case of spontaneous generation and in the presence of a seed beam. Then we review three types of optical fibers and we examine their properties in terms of conversion efficiency and practical feasibility.
CRIS-Team WoS Importer:2020-04-10

Proof-of-principle test of coherent-state continuous variable quantum key distribution through turbulent atmosphere - Derkach, Ivan; Peuntinger, Christian; Ruppert, Laszlo; Heim, Bettina; Gunthner, Kevin; Usenko, Vladyslav C.; Elser, Dominique; Marquardt, Christoph; Filip, Radim; Leuchs, Gerd (SPIE Security + Defence, 2016)
Continuous-variable quantum key distribution is a practical application of quantum information theory that is aimed at generation of secret cryptographic key between two remote trusted parties and that uses multi-photon quantum states as carriers of key bits. Remote parties share the secret key via a quantum channel, that presumably is under control of of an eavesdropper, and which properties must be taken into account in the security analysis. Well-studied fiber-optical quantum channels commonly possess stable transmittance and low noise levels, while free-space channels represent a simpler, less demanding and more flexible alternative, but suffer from atmospheric effects such as turbulence that in particular causes a non-uniform transmittance distribution referred to as fading. Nonetheless free-space channels, providing an unobstructed line-of-sight, are more apt for short, mid-range and potentially long-range (using satellites) communication and will play an important role in the future development and implementation of QKD networks. It was previously theoretically shown that coherent-state CV QKD should be in principle possible to implement over a free-space fading channel, but strong transmittance fluctuations result in the significant modulation-dependent channel excess noise. In this regime the post-selection of highly transmitting sub-channels may be needed, which can even restore the security of the protocol in the strongly turbulent channels. We now report the first proof-of-principle experimental test of coherent state CV QKD protocol using different levels Gaussian modulation over a mid-range (1.6-kilometer long) free-space atmospheric quantum channel. The transmittance of the link was characterized using intensity measurements for the reference but channel estimation using the modulated coherent states was also studied. We consider security against Gaussian collective attacks, that were shown to be optimal against CV QKD protocols . We assumed a general entangling cloner collective attack (modeled using data obtained from the state measurement results on both trusted sides of the protocol), that allows to purify the noise added in the quantum channel . Our security analysis of coherent-state protocol also took into account the effect of imperfect channel estimation, limited post-processing efficiency and finite data ensemble size on the performance of the protocol. In this regime we observe the positive key rate even without the need of applying post-selection. We show the positive improvement of the key rate with increase of the modulation variance, still remaining low enough to tolerate the transmittance fluctuations. The obtained results show that coherent-state CV QKD protocol that uses real free-space atmospheric channel can withstand negative influence of transmittance fluctuations, limited post-processing efficiency, imperfect channel estimation and other finite-size effects, and be successfully implemented. Our result paves the way to the full-scale implementation of the CV QKD in real free-space channels at mid-range distances.<br

Propagation of broadband sub-picosecond soliton squeezing in a fiber - Leuchs, Gerd; et al. (Optics Express, 1998)
UnivIS-Import:2015-03-05:Pub.1998.nat.dphy.optik.1optik.propag

Propagation of Quantum Properties of Sub-Picosecond Solitons in a Fibre - Leuchs, Gerd; et al. (Optics Express, 1998)
We present new results on photon number squeezing of spectrally filtered solitons in fibers. The impact of frequency low-, high-, and bandpass filtering on noise reduction has been measured as a function of fiber length for 130-fs pulses close to the soliton energy. For short fibers our results agree qualitatively with theoretical predictions. For longer fibers, however, the measured squeezing increases to an unexpectedly large value. Spectral filtering of a strongly Raman-shifted, higher energy pulse squeezed the directly detected photocurrent fluctuations down to 3.8±0.2 dB (59%) below the shot noise level. The measured noise reductions are broadband from 5 to 90 MHz. © 1997 Optical Society of America.
UnivIS-Import:2015-03-05:Pub.1998.nat.dphy.optik.1optik.propag_4

Properties of bright squeezed vacuum at increasing brightness - Sharapova, P. R.; Frascella, Gaetano; Riabinin, M.; Perez, A. M.; Tikhonova, Olga; Lemieux, S.; Boyd, R. W.; Leuchs, Gerd; Chekhova, Maria (Physical Review Research, 2020)
A bright squeezed vacuum (BSV) is a nonclassical macroscopic state of light, which is generated through high-gain parametric down-conversion or four-wave mixing. Although the BSV is an important tool in quantum optics and has a lot of applications, its theoretical description is still not complete. In particular, the existing description in terms of Schmidt modes with gain-independent shapes fails to explain the spectral broadening observed in the experiment as the mean number of photons increases. Meanwhile, the semiclassical description accounting for the broadening does not allow us to decouple the intermodal photon-number correlations. In this work, we present a new generalized theoretical approach to describe the spatial properties of a multimode BSV. In the multimode case, one has to take into account the complicated interplay between all involved modes: each plane-wave mode interacts with all other modes, which complicates the problem significantly. The developed approach is based on exchanging the (k, t) and (omega, z) representations and solving a system of integrodifferential equations. Our approach predicts correctly the dynamics of the Schmidt modes and the broadening of the angular distribution with the increase in the BSV mean photon number due to a stronger pumping. Moreover, the model correctly describes various properties of a widely used experimental configuration with two crystals and an air gap between them, namely, an SU(1,1) interferometer. In particular, it predicts the narrowing of the intensity distribution, the reduction and shift of the side lobes, and the decline in the interference visibility as the mean photon number increases due to stronger pumping. The presented experimental results confirm the validity of the new approach. The model can be easily extended to the case of the frequency spectrum, frequency Schmidt modes, and other experimental configurations.
CRIS-Team WoS Importer:2021-01-15

Proposal for a hybrid clock system consisting of passive and active optical clocks and a fully stabilized microcomb - Yu, Deshui; Vollmer, Frank; Del'Haye, Pascal; Zhang, Shougang (Optics Express, 2023)
Optical atomic clocks produce highly stable frequency standards and frequency combs bridge clock frequencies with hundreds of terahertz difference. In this paper, we propose a hybrid clock scheme, where a light source pumps an active optical clock through a microresonator-based nonlinear third harmonic process, serves as a passive optical clock via indirectly locking its frequency to an atomic transition, and drives a chip-scale microcomb whose mode spacing is stabilized using the active optical clock. The operation of the whole hybrid system is investigated through simulation analysis. The numerical results show: (i) The short-term frequency stability of the passive optical clock follows an Allan deviation of σy(τ) = 9.3 × 10−14τ−1/2 with the averaging time τ, limited by the population fluctuations of interrogated atoms. (ii) The frequency stability of the active optical clock reaches σy(τ) = 6.2 × 10−15τ−1/2, which is close to the quantum noise limit. (iii) The mode spacing of the stabilized microcomb has a shot-noise-limited Allan deviation of σy(τ) = 1.9 × 10−11τ−1/2. Our hybrid scheme may be realized using recently developed technologies in (micro)photonics and atomic physics, paving the way towards on-chip optical frequency comparison, synthesis, and synchronization.
CRIS-Team Scopus Importer:2023-02-24

Prospect for detecting squeezed states of light created by a single atom in free space - Stobinska, Magdalena; Sondermann, Markus; Leuchs, Gerd (Optics Communications, 2010)
We discuss the possibilities of studying in detail the dynamics of spontaneous emission of a single photon by a single atom and measuring the transient degree of squeezing by means of full solid angle fluorescence detection. © 2009 Elsevier B.V. All rights reserved.
UnivIS-Import:2015-03-09:Pub.2010.nat.dphy.optik.1optik.prospe
Keywords: Resonance fluorescence; Single atom; Single photon; Squeezing

Prospects of Trapping Atoms with an Optical Dipole Trap in a Deep Parabolic Mirror for Light-Matter-Interaction Experiments - Sondermann, Markus; Fischer, Martin; Leuchs, Gerd (Advanced Quantum Technologies, 2020)
Keywords: light-matter interaction; optical trapping; parabolic mirror

Publisher Correction: Resonant electro-optic frequency comb (Nature, (2019), 568, 7752, (378-381), 10.1038/s41586-019-1110-x) - Rueda, Alfredo; Sedlmeir, Florian; Kumari, Madhuri; Leuchs, Gerd; Schwefel, Harald G.L. (Nature, 2019)
Change history: In the Methods section of this Letter, there were formatting errors to the equations of motion using the Heisenberg picture; see accompanying Amendment for further details. This has been corrected online.
CRIS-Team Scopus Importer:2019-05-28

Pump depletion in parametric down-conversion with low pump energies - Florez, Jefferson; Lundeen, Jeff S.; Chekhova, Maria (Optics Letters, 2020)
We report the efficient generation of high-gain parametric down-conversion, including pump depletion, with pump powers as low as 100 µW (energies 0.1 µJ/pulse) and conversion efficiencies up to 33%. In our simple configuration, the pump beam is tightly focused into a bulk periodically poled lithium niobate crystal placed in free space. We also observe a change in the photon number statistics for both the pump and down-converted beams as the pump power increases to reach the depleted pump regime. The experimental results are a clear signature of the interplay between the pump and the down-converted beams in highly efficient parametric down-conversion sources.
CRIS-Team Scopus Importer:2020-09-18

QPSK receiver outperforming the standard quantum limit for any signal power - Muller, Christian R.; Leuchs, Gerd; Marquardt, Christoph (Optics InfoBase Conference Papers, 2014)
We present a quantum receiver for the discrimination of quadrature phase-shiftkeyed signals that approaches the Helstrom bound for any signal power. The discrimination isperformed via adaptive displacements prior to a single photon detector. © 2014 Optical Society of America.
CRIS-Team Scopus Importer:2022-06-05

Quadrature measurements of a bright squeezed state via sideband swapping - Leuchs, Gerd; et al. (Optics Letters, 2009)
The measurement of an arbitrary quadrature of a bright quantum state of light is a commonly requested action in many quantum information protocols, but it is experimentally challenging with previously proposed schemes. We suggest that the quadrature be measured at a specific sideband frequency of a bright quantum state by transferring the sideband modes under interrogation to a vacuum state and subsequently measuring the quadrature via homodyne detection. The scheme is implemented experimentally, and it is successfully tested with a bright squeezed state of light. © 2009 Optical Society of America.
UnivIS-Import:2015-03-09:Pub.2009.nat.dphy.optik.1optik.quadra

Quadrature phase shift keying coherent state discrimination via a hybrid receiver - Müller, Christian; Usuga, M. A.; Wittmann, Christoffer; Takeoka, M.; Marquardt, Christoph; Andersen, U. L.; Leuchs, Gerd (New Journal of Physics, 2012)
We propose and experimentally demonstrate a near-optimal discrimination scheme for the quadrature phase shift keying (QPSK) protocol. We show in theory that the performance of our hybrid scheme is superior to the standard scheme-heterodyne detection-for all signal amplitudes and underpin the predictions with our experimental results. Furthermore, our scheme provides hitherto the best performance in the domain of highly attenuated signals. The discrimination is composed of a quadrature measurement, a conditional displacement and a threshold detector. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
CRIS-Team Scopus Importer:2022-06-05

Quantencomputer heute und in Zukunft - Eichler, Christopher (2022)
Keywords: wwwquantum

Quantencomputer: Von Schrödingers Katze zu Hochleistungsrechnern der Zukunft. - Eichler, Christopher (2023)

Quantenrauschberuhigtes Licht - Leuchs, Gerd; et al. (Design & Elektronik, 2000)
UnivIS-Import:2015-03-09:Pub.2000.nat.dphy.optik.1optik.quante

Quantitative broadband chemical sensing in air-suspended solid-core fibers - Euser, Tijmen; Chen, J. S. Y.; Scharrer, Michael; Russell, Philip St. John; Farrer, N. J.; Sadler, P. J. (Journal of Applied Physics, 2008)
We demonstrate a quantitative broadband fiber sensor based on evanescent-field sensing in the cladding holes of an air-suspended solid-core photonic crystal fiber. We discuss the fabrication process, together with the structural and optical characterization of a range of different fibers. Measured mode profiles are in good agreement with finite element method calculations made without free parameters. The fraction of the light in the hollow cladding can be tuned via the core diameter of the fiber. Dispersion measurements are in excellent agreement with theory and demonstrate tuning of the zero dispersion wavelength via the core diameter. Optimum design parameters for absorption sensors are discussed using a general parameter diagram. From our analysis, we estimate that a sensitivity increase of three orders of magnitude is feasible compared to standard cuvette measurements. Our study applies to both liquid and gas fiber sensors. We demonstrate the applicability of our results to liquid chemical sensing by measuring the broad absorption peak of an aqueous NiCl2 solution. We find excellent agreement with the reference spectrum measured in a standard cuvette, even though the sample volume has decreased by three orders of magnitude. Our results demonstrate that air-suspended solid-core photonic crystal fibers can be used in quantitative broadband chemical-sensing measurements.
EAM Import::2019-03-12

Quantum communication with coherent states of light - Khan, Imran; Elser, Dominique; Dirmeier, Thomas; Marquardt, Christoph; Leuchs, Gerd (Philosophical Transactions of the Royal Society A-Mathematical Physical and Engineering Sciences, 2017)
Quantum communication offers long-term security especially, but not only, relevant to government and industrial users. It is worth noting that, for the first time in the history of cryptographic encoding, we are currently in the situation that secure communication can be based on the fundamental laws of physics (information theoretical security) rather than on algorithmic security relying on the complexity of algorithms, which is periodically endangered as standard computer technology advances. On a fundamental level, the security of quantum key distribution (QKD) relies on the non-orthogonality of the quantum states used. So even coherent states are well suited for this task, the quantum states that largely describe the light generated by laser systems. Depending on whether one uses detectors resolving single or multiple photon states or detectors measuring the field quadratures, one speaks of, respectively, a discrete- or a continuous-variable description. Continuous-variable QKD with coherent states uses a technology that is very similar to the one employed in classical coherent communication systems, the backbone of today's Internet connections. Here, we review recent developments in this field in two connected regimes: (i) improving QKD equipment by implementing front-end telecom devices and (ii) research into satellite QKD for bridging long distances by building upon existing optical satellite links.
CRIS-Team Scopus Importer:2022-06-05
Keywords: Coherent states; Continuous variables; Quantum communication

Quantum Communication with continuous variables using multi-photonstates of light - Leuchs, Gerd; et al. (Proc. of the 15th European Meeting on Cybernetics and Systems Research, 2000)
UnivIS-Import:2015-04-16:Pub.2000.nat.dphy.optik.1optik.quantu

Quantum correlations in separable multi-mode states and in classically entangled light - Korolkova, N.; Leuchs, Gerd (Reports on Progress in Physics, 2019)
In this review we discuss intriguing properties of apparently classical optical fields, that go beyond purely classical context and allow us to speak about quantum characteristics of such fields and about their applications in quantum technologies. We briefly define the genuinely quantum concepts of entanglement and steering. We then move to the boarder line between classical and quantum world introducing quantum discord, a more general concept of quantum coherence, and finally a controversial notion of classical entanglement. To unveil the quantum aspects of often classically perceived systems, we focus more in detail on quantum discordant correlations between the light modes and on nonseparability properties of optical vector fields leading to entanglement between different degrees of freedom of a single beam. To illustrate the aptitude of different types of correlated systems to act as quantum or quantum-like resource, entanglement activation from discord, high-precision measurements with classical entanglement and quantum information tasks using intra-system correlations are discussed. The common themes behind the versatile quantum properties of seemingly classical light are coherence, polarization and inter and intra-mode quantum correlations.
CRIS-Team WoS Importer:2019-04-23

Quantum cryptography with bright entangled beams - Leuchs, Gerd; et al. (IQEC'2000 Conference Digest, 2000)
A scheme for the generation of bright entangled beams is discussed. The Einstein-Podolsky-Rosen (EPR) quantum correlations are produced by letting two amplitude-squeezed bright optical fields interfere on a 50:50 beamsplitter. This is illustrated in the phase space representation in a single-mode picture. The phase and amplitude uncertainty measurements exhibit strong correlations and anticorrelations which can be detected by recording the difference of the photocurrents.
UnivIS-Import:2015-04-16:Pub.2000.nat.dphy.optik.1optik.quantu_2

Quantum cryptography with twisted photons through an outdoor underwater channel - Bouchard, Frederic; Sit, Alicia; Hufnagel, Felix; Abbas, Aazad; Zhang, Yingwen; Heshami, Khabat; Fickler, Robert; Marquardt, Christoph; Leuchs, Gerd; Boyd, Robert W.; Karimi, Ebrahim (Optics Express, 2018)
Quantum communication has been successfully implemented in optical fibres and through free-space. Fibre systems, though capable of fast key and low error rates, are impractical in communicating with destinations without an established fibre link. Free-space quantum channels can overcome such limitations and reach long distances with the advent of satellite-to-ground links. However, turbulence, resulting from local fluctuations in refractive index, becomes a major challenge by adding errors and losses. Recently, an interest in investigating the possibility of underwater quantum channels has arisen. Here, we investigate the effect of turbulence on an underwater quantum channel using twisted photons in outdoor conditions. We study the effect of turbulence on transmitted error rates, and compare different quantum cryptographic protocols in an underwater quantum channel, showing the feasibility of high-dimensional encoding schemes. Our work may open the way for secure high-dimensional quantum communication between submersibles, and provides important input for potential submersibles-to-satellite quantum communication.
CRIS-Team Scopus Importer:2022-06-05

Quantum effects in optical fibers - Leuchs, Gerd; Marquardt, Christoph (Optics InfoBase Conference Papers, 2011)
The quantization of the light field is important for understanding some aspects of optical fiber systems: the quantum limit of amplifiers, the dynamics of solitons below shot noise and the appearance of non-classical light. © OSA/OFC/NFOEC 2011.
CRIS-Team Scopus Importer:2022-06-05

Quantum Efficiency of Single Dibenzoterrylene Molecules in p-Dichlorobenzene at Cryogenic Temperatures - Musavinezhad, Mohammad; Shkarin, Alexey; Rattenbacher, Dominik; Renger, Jan; Utikal, Tobias; Götzinger, Stephan; Sandoghdar, Vahid (Journal of Physical Chemistry B, 2023)
We measure the quantum efficiency (QE) of individual dibenzoterrylene (DBT) molecules embedded in p-dichlorobenzene at cryogenic temperatures. To achieve this, we combine two distinct methods based on the maximal photon emission and on the power required to saturate the zero-phonon line to compensate for uncertainties in some key system parameters. We find that the outcomes of the two approaches are in good agreement for reasonable values of the parameters involved, reporting a large fraction of molecules with QE values above 50%, with some exceeding 70%. Furthermore, we observe no correlation between the observed lower bound on the QE and the lifetime of the molecule, suggesting that most of the molecules have a QE exceeding the established lower bound. This confirms the suitability of DBT for quantum optics experiments. In light of previous reports of low QE values at ambient conditions, our results hint at the possibility of a strong temperature dependence of the QE.
CRIS-Team Scopus Importer:2023-07-21

Quantum fiber solitons - generation, entanglement and detection - Leuchs, Gerd; Korolkova, Natalia; Glöckl, Oliver; Lorenz, Stefan; Heersink, Joel; Silberhorn, Christine; Marquardt, Christoph; Andersen, Ulrik L. (Quantum Information Processing: Schwerpunktprogramm 1078 der Deutschen Forschungsgemeinschaft, 2005)
UnivIS-Import:2015-04-20:Pub.2005.nat.dphy.optik.1optik.quantu_4
Keywords: Bright entangled beams; Entanglement of bright beams; Entanglement swapping; Non-separability; Polarization variables; Quantum correlations; Quantum fiber solitons; Quantum information processing; Sub-shot-noise phase quadrature measurements on intense beams

Quantum field theory and classical optics: Determining the fine structure constant - Leuchs, Gerd; Hawton, Margaret; Sanchez-Soto, Luis L. (Journal of Physics: Conference Series, 2017)
The properties of the vacuum are described by quantum physics including the response to external fields such as electromagnetic radiation. Of the two parameters that govern the details of the electromagnetic field dynamics in vacuum, one is fixed by the requirement of Lorentz invariance . The other one, and its relation to the quantum vacuum, is discussed in this contribution. Deriving ϵ 0 from the properties of the quantum vacuum implies the derivation of the fine structure constant.
CRIS-Team Scopus Importer:2023-04-20

Quantum filtering of optical coherent states - Leuchs, Gerd; et al. (Physical Review A, 2008)
We propose and experimentally demonstrate nondestructive and noiseless removal (filtering) of vacuum states from an arbitrary set of coherent states of continuous variable systems. Errors, i.e., vacuum states in the quantum information are diagnosed through a weak measurement, and on that basis, probabilistically filtered out. We consider three different filters based on on-off detection, phase stabilized, and phase randomized homodyne detection. We find that on-off detection, optimal in the ideal theoretical setting, is superior to the homodyne strategy also in a practical setting. © 2008 The American Physical Society.
UnivIS-Import:2015-03-09:Pub.2008.nat.dphy.optik.1optik.quantu

Quantum hacking of continuous-variable quantum key distribution systems: Realtime Trojan-horse attacks - Stiller, Birgit; Khan, Imran; Jain, Nitin; Jouguet, P.; Kunz-Jacques, S.; Diamanti, E.; Marquardt, Christoph; Leuchs, Gerd (Conference on Lasers and Electro-Optics Europe - Technical Digest, 2015)
We experimentally demonstrate successful Trojan-horse attacks on laboratory and commercial continuous-variable quantum key distribution systems with binary and Gaussian modulation. Furthermore, we analyze appropriate countermeasures regarding their spectral performance.
CRIS-Team Scopus Importer:2021-06-29
Keywords: Optical pulses; Optical refraction; Optical variables control; Phase modulation; Protocols; Security

Quantum imaging with incoherently scattered light from a free-electron laser - Schneider, Raimund; Mehringer, Thomas; Mercurio, Giuseppe; Wenthaus, Lukas; Classen, Anton; Brenner, Gunter; Gorobtsov, Oleg; Benz, Adrian; Bhatti, Daniel; Bocklage, Lars; Fischer, Birgit; Lazarev, Sergey; et al. (Nature Physics, 2018)
The advent of accelerator-driven free-electron lasers (FEL) has opened new avenues for high-resolution structure determination via diffraction methods that go far beyond conventional X-ray crystallography methods(1-10). These techniques rely on coherent scattering processes that require the maintenance of first-order coherence of the radiation field throughout the imaging procedure. Here we show that higher-order degrees of coherence, displayed in the intensity correlations of incoherently scattered X-rays from an FEL, can be used to image two-dimensional objects with a spatial resolution close to or even below the Abbe limit. This constitutes a new approach towards structure determination based on incoherent processes(11,12), including fluorescence emission or wavefront distortions, generally considered detrimental for imaging applications. Our method is an extension of the landmark intensity correlation measurements of Hanbury Brown and Twiss(13) to higher than second order, paving the way towards determination of structure and dynamics of matter in regimes where coherent imaging methods have intrinsic limitations(14).

Quantum imaging with incoherent photons - Thiel, Christoph; Bastin, Thierry; Martin, J; Solano, Enrique; von Zanthier, Joachim; Agarwal, Girish S. (Physical Review Letters, 2007)
We propose a technique to obtain subwavelength resolution in quantum imaging with potentially 100% contrast using incoherent light. Our method requires neither path-entangled number states nor multiphoton absorption. The scheme makes use of N photons spontaneously emitted by N atoms and registered by N detectors. It is shown that for coincident detection at particular detector positions a resolution of lambda/N can be achieve

Quantum Information From Foundations to Quantum Technology Applications Preface to the New Edition - Bruss, Dagmar; Leuchs, Gerd (Quantum Information: From Foundations to Quantum Technology Applications, 2019)
CRIS-Team WoS Importer:2020-09-25

Quantum information processing and communication, Strategic report on current status, visions and goals for research in Europe - Leuchs, Gerd; et al. (European Physical Journal D, 2005)
We present an excerpt of the document "Quantum Information Processing and Communication: Strategic report on current status, visions and goals for research in Europe", which has been recently published in electronic form at the website of FET (the Future and Emerging Technologies Unit of the Directorate General Information Society of the European Commission, http://www.cordis.lu/ist/fet/qipc-sr.htm). This document has been elaborated, following a former suggestion by FET, by a committee of QIPC scientists to provide input towards the European Commission for the preparation of the Seventh Framework Program. Besides being a document addressed to policy makers and funding agencies (both at the European and national level), the document contains a detailed scientific assessment of the state-of-the-art, main research goals, challenges, strengths, weaknesses, visions and perspectives of all the most relevant QIPC sub-fields, that we report here. Dedicated to the memory of Prof. Th. Beth, one of the pioneers of QIPC, whose contributions have had a significant scientific impact on the development as well as on the visibility of a field that he enthusiastically helped to shape since its early days. © EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2005.
UnivIS-Import:2015-03-09:Pub.2005.nat.dphy.optik.1optik.quantu_2

Quantum Information Processing - Leuchs, Gerd; et al. (Wiley-VCH, 2003)
UnivIS-Import:2015-04-02:Pub.2003.nat.dphy.optik.1optik.quantu_6

Quantum Information Processing - Leuchs, Gerd; et al. (Wiley-VCH, 2003)
UnivIS-Import:2015-05-08:Pub.2003.nat.dphy.optik.1optik.quantu_7

Quantum Information Processing: Schwerpunktprogramm 1078 der Deutschen Forschungsgemeinschaft - Leuchs, Gerd; et al. (Wiley-VCH Verlag GmbH &Co KGaA, 2005)
UnivIS-Import:2015-04-02:Pub.2005.nat.dphy.optik.1optik.quantu

Quantum Information Processing: Schwerpunktprogramm 1078 der Deutschen Forschungsgemeinschaft - Leuchs, Gerd; et al. (Wiley-VCH Verlag GmbH & Co KGaA, 2005)
UnivIS-Import:2015-05-08:Pub.2005.nat.dphy.optik.1optik.quantu_0

Quantum Information Processing with Superconducting Circuits - Eichler, Christopher (GDR IQFA - 9th Colloquium, 2018)
Keywords: wwwqudev

Quantum Information with Continuous Variables of Atoms and Light - Leuchs, Gerd; et al. (Imperial College Press, 2007)
UnivIS-Import:2015-04-02:Pub.2007.nat.dphy.optik.1optik.quantu

Quantum interference and entanglement of photons that do not overlap in time - Wiegner, Ralph; Thiel, Christoph; von Zanthier, Joachim; Agarwal, G. S. (Optics Letters, 2011)
We discuss the possibility of quantum interferences and entanglement of photons that exist at different intervals of time, i.e., one photon being recorded before the other has been created. The corresponding two-photon correlation function is shown to violate Bell's inequalities. (c) 2011 Optical Society of America

Quantum interference and non-locality of independent photons from disparate sources - Wiegner, Ralph; von Zanthier, Joachim; Agarwal, G. S. (Journal of Physics B-Atomic Molecular and Optical Physics, 2011)
We quantitatively investigate the non-classicality and non-locality of a whole new class of mixed disparate quantum and semiquantum photon sources at the quantum-classical boundary. The latter include photon-added thermal and photon-added coherent sources, experimentally investigated recently by Zavatta et al (2009 Phys. Rev. Lett. 103 140406). The key quantity in our investigations is the visibility of the corresponding photon-photon correlation function. We present explicit results on the violations of the Cauchy-Schwarz inequality-which is a measure of non-classicality-as well as of Bell-type inequalitie

Quantum-interference-initiated superradiant and subradiant emission from entangled atoms - Wiegner, Ralph; von Zanthier, Joachim; Agarwal, G. S. (Physical Review A, 2011)
We calculate the radiative characteristics of emission from a system of entangled atoms which can have a relative distance larger than the emission wavelength. We develop a quantum multipath interference approach which explains both super-and subradiance though the entangled states have zero dipole moment. We derive a formula for the radiated intensity in terms of different interfering pathways. We further show how the interferences lead to directional emission from atoms prepared in symmetric W states. As a byproduct of our work we show how Dicke's classic result can be understood in terms of interfering pathways. In contrast to the previous works on ensembles of atoms, we focus on finite numbers of atoms prepared in well characterized state

Quantum interferometry - Leuchs, Gerd; et al. (Lectures on Quantum Information, 2006)
UnivIS-Import:2015-04-20:Pub.2006.nat.dphy.optik.1optik.quantu

Quantum interferometry with fiber solitons - a direct experimental test of non-separability - Leuchs, Gerd; et al. (Proceedings of the 8th Rochester Conference on Coherence and Quantum Optics, 2002)
UnivIS-Import:2015-04-16:Pub.2002.nat.dphy.optik.1optik.uantum

Quantum Interferometry with Gaussian States - Andersen, Ulrik L.; Gloeckl, Oliver; Gehring, Tobias; Leuchs, Gerd (Quantum Information: From Foundations to Quantum Technology Applications, 2019)
CRIS-Team WoS Importer:2020-09-25

Quantum interferometry with intense optical pulses - Leuchs, Gerd; et al. (Fortschritte Der Physik-Progress of Physics, 2003)
For intense optical pulses the optical Kerr interaction in matter such as an optical fiber is large enough to generate quantum states of light with significant non-classical properties. On this basis pairs of entangled light pulses have been generated. This entanglement can be used for novel schemes in high precision interferometry and for quantum communication protocols such as quantum dense coding.
UnivIS-Import:2015-03-09:Pub.2003.nat.dphy.optik.1optik.quantu

Quantum key distribution with bright entangled beams - Leuchs, Gerd; et al. (Physical Review Letters, 2002)
Continuous electron paramagnetic resonance (EPR)-like correlations of bright optical beams were used to suggest a quantum cryptographic scheme. The continuous information was discretized in a novel way by associating a respective measurement, amplitude, or phase, with a bit value 1 or 0 for binary key encoding. The binary bits were encoded by the choice to detect either of two conjugate variables accomplished independently and randomly by both communicating parties. The implementation of the scheme was experimentally simple, robust and well-suited for fiber-integrated or free-space transmission.
UnivIS-Import:2015-03-09:Pub.2002.nat.dphy.optik.1optik.quantu

Quantum Light from a Whispering-Gallery-Mode Disk Resonator - Fuerst, J. U.; Strekalov, D. V.; Elser, Dominique; Aiello, Andrea; Andersen, U. L.; Marquardt, Christoph; Leuchs, Gerd (Physical Review Letters, 2011)
Optical parametric down-conversion has proven to be a valuable source of nonclassical light. The process is inherently able to produce twin-beam correlations along with individual intensity squeezing of either parametric beam, when pumped far above threshold. Here, we present for the first time the direct observation of intensity squeezing of -1.2dB of each of the individual parametric beams in parametric down-conversion by use of a high quality whispering-gallery-mode disk resonator. In addition, we observed twin-beam quantum correlations of -2.7dB with this cavity. Such resonators feature strong optical confinement and offer tunable coupling to an external optical field. This work exemplifies the potential of crystalline whispering-gallery-mode resonators for the generation of quantum light. The simplicity of this device makes the application of quantum light in various fields highly feasible. © 2011 American Physical Society.
CRIS-Team Scopus Importer:2022-06-05

Quantum-like nonseparable structures in optical beams - Aiello, Andrea; Töppel, Falk; Marquardt, Christoph; Giacobino, Elisabeth; Leuchs, Gerd (New Journal of Physics, 2015)
When two or more degrees of freedom become coupled in a physical system, a number of observables of the latter cannot be represented by mathematical expressions separable with respect to the different degrees of freedom. In recent years it appeared clear that these expressions may display the same mathematical structures exhibited by multiparty entangled states in quantum mechanics. In this work, we investigate the occurrence of such structures in optical beams, a phenomenon that is often referred to as 'classical entanglement'. We present a unified theory for different kinds of light beams exhibiting classical entanglement and we indicate several possible extensions of the concept. Our results clarify and shed new light upon the physics underlying this intriguing aspect of classical optics.
CRIS-Team Scopus Importer:2022-06-05
Keywords: classical entanglement; non-separability; optical beams

Quantum limited amplification and entanglement of microwave fields with coupled nonlinear cavities - Eichler, Christopher (2014)
Coupled nonlinear cavities provide a versatile testbed to study fundamental light-matter interactions and constitute a generic building block to realize photonic quantum simulators for strongly interacting systems. Their theoretical investigation and experimental realizations have therefore been driven forward in a variety of physical settings. In my talk I will present the implementation of a dissipative Bose-Hubbard dimer in superconducting circuits to achieve quantum limited amplification and to generate frequency entangled microwave photon pairs. Featuring a flexible control over the relevant system parameters, the presented lumped element circuit has also great potential to be used as an elementary cell in larger nonlinear cavity arrays. In contrast to previous implementations of microwave parametric amplifiers our device can be operated both as a bsingle mode squeezer and as a nondegenerate phase-preserving amplifier. In combination with its large achievable bandwidth, tunability and saturation power our device may find broad application in experiments aiming at quantum limited detection – particularly in superconducting circuits. Collaborators: Y. Salathe, J. Mlynek, S. Schmidt, Wallraff, A.
Keywords: wwwqudev

Quantum Limited Amplification, Vacuum Squeezing, and Frequency Conversion in Parametrically Driven Superconducting Circuits - Eichler, Christopher (Workshop on Parametric phenomena, 2017)
Keywords: wwwqudev

Quantum-limited measurements of intensity noise levels in Yb-doped fiber amplifiers - Popp, Alexandra; Distler, Victor; Jaksch, Kevin; Sedlmeir, Florian; Mueller, Christian R.; Haarlammert, Nicoletta; Schreiber, Thomas; Marquardt, Christoph; Tuennermann, Andreas; Leuchs, Gerd (Applied Physics B-Lasers and Optics, 2020)
We investigate the frequency-resolved intensity noise spectrum of an Yb-doped fiber amplifier down to the fundamental limit of quantum noise. We focus on the kHz and low MHz frequency regime with special interest in the region between 1 and 10 kHz. Intensity noise levels up to ≥ 60 dB above the shot noise limit are found, revealing great optimization potential. Additionally, two seed lasers with different noise characteristics were amplified, showing that the seed source has a significant impact and should be considered in the design of high power fiber amplifiers.
CRIS-Team Scopus Importer:2020-07-24

Quantum-limited measurements of optical signals from a geostationary satellite - Günthner, Kevin; Khan, Imran; Elser, Dominique Alexander; Stiller, Birgit; Bayraktar, Ömer; Mueller, Christian R.; Saucke, Karen; Troendle, Daniel; Heine, Frank; Seel, Stefan; Greulich, Peter; Zech, Herwig; et al. (Optica, 2017)
The measurement of quantum signals that travel through long distances is fundamentally and technologically interesting. We present quantum-limited coherent measurements of optical signals that are sent from a satellite in geostationary Earth orbit to an optical ground station. We bound the excess noise that the quantum states could have acquired after having propagated 38,600 km through Earth’s gravitational potential, as well as its turbulent atmosphere. Our results indicate that quantum communication is feasible, in principle, in such a scenario, highlighting the possibility of a global quantum key distribution network for secure communication.
CRIS-Team Scopus Importer:2021-06-29
Keywords: (010.1300) Atmospheric propagation; (060.1660) Coherent communications; (060.2605) Free-space optical communication; (270.5565) Quantum communications; (270.5568) Quantum cryptography

Quantum-limited measurements of optical signals from a satellite in geostationary earth orbit - Günthner, Kevin; Khan, Imran; Elser, Dominique; Stiller, Birgit; Bayraktar, Ömer; Müller, Christian; Saucke, Karen; Tröndle, Daniel; Heine, Frank; Seel, Stefan; Greulich, Peter; Zech, Herwig; et al. (Optics InfoBase Conference Papers, 2017)
CRIS-Team Scopus Importer:2021-06-29

Quantum-limited measurements of signals from geostationary earth orbit - Elser, Dominique; Günthner, Kevin; Khan, Imran; Stiller, Birgit; Bayraktar, Ömer; Müller, Christian; Saucke, Karen; Tröndle, Daniel; Heine, Frank; Seel, Stefan; Greulich, Peter; Zech, Herwig; et al. (European Conference on Optical Communication, ECOC, 2016)
Quantum key distribution (QKD) has been implemented in metropolitan area networks around the world. Optical satellite communication is seen as suitable to provide the missing long-haul interconnections. We validate this approach by quantum measurements of optical signals from space.
CRIS-Team Scopus Importer:2021-06-29

Quantum Limits of Coherent Beam Combining - Leuchs, Gerd; Müller, Christian; Sedlmeir, Florian; Chatterjee, Sourav; Haarlammert, Nicoletta; Jauregui, Cesar; Schreiber, Thomas; Limpert, Jens; Tunnermann, Andreas; Marquardt, Christoph (2018 Conference on Lasers and Electro-Optics Pacific Rim, CLEO-PR 2018, 2019)
Coherent beam combining refers to the process of generating a bright output beam by merging independent input beams with locked relative phases. We report the first quantum mechanical noise limit calculations for coherent beam combining and compare our results to quantum-limited amplification. We highlight a favourable noise scaling for both pure and noisy input states.
CRIS-Team Scopus Importer:2019-05-21

Quantum limits to center-of-mass measurements - Leuchs, Gerd; et al. (Physical Review A, 2008)
UnivIS-Import:2015-03-09:Pub.2008.nat.dphy.optik.1optik.quantu_8

Quantum measurements of signals from the Alphasat TDP1 laser communication terminal - Elser, D.; Günthner, Kevin; Khan, Imran; Stiller, Birgit; Bayraktar, Ömer; Müller, Christian; Saucke, K.; Tröndle, D.; Heine, F.; Seel, S.; Greulich, P.; Zech, H.; et al. (Proceedings of SPIE - The International Society for Optical Engineering, 2017)
Quantum optics [1] can be harnessed to implement cryptographic protocols that are verifiably immune against any conceivable attack [2]. Even quantum computers, that will break most current public keys [3, 4], cannot harm quantum encryption. Based on these intriguing quantum features, metropolitan quantum networks have been implemented around the world [5-15]. However, the long-haul link between metropolitan networks is currently missing [16]. Existing fiber infrastructure is not suitable for this purpose since classical telecom repeaters cannot relay quantum states [2]. Therefore, optical satellite-to-ground communication [17-22] lends itself to bridge intercontinental distances for quantum communication [23-40].
CRIS-Team Scopus Importer:2021-06-29

Quantum Metamaterials with Magnetic Response at Optical Frequencies - Alaee, Rasoul; Gurlek, Burak; Albooyeh, Mohammad; Martin-Cano, Diego; Sandoghdar, Vahid (Physical Review Letters, 2020)
We propose novel quantum antennas and metamaterials with a strong magnetic response at optical frequencies. Our design is based on the arrangement of natural quantum emitters with only electric dipole transition moments at distances smaller than a wavelength of light but much larger than their physical size. In particular, we show that an atomic dimer can serve as a magnetic antenna at its antisymmetric mode to enhance the decay rate of a magnetic transition in its vicinity by several orders of magnitude. Furthermore, we study metasurfaces composed of atomic bilayers with and without cavities and show that they can fully reflect the electric and magnetic fields of light, thus, forming nearly perfect electric or magnetic mirrors. The proposed metamaterials will embody the intrinsic quantum functionalities of natural emitters such as atoms, ions, color center, or molecules and can be fabricated with available state-of-the-art technologies, promising several applications both in classical optics and quantum engineering.
CRIS-Team WoS Importer:2020-08-28

Quantum nature of Gaussian discord: Experimental evidence and role of system-environment correlations - Chille, Vanessa; Quinn, Niall; Peuntinger, Christian; Croal, Callum; Mista, Ladislav; Marquardt, Christoph; Leuchs, Gerd; Korolkova, Natalia (Physical Review A - Atomic, Molecular, and Optical Physics, 2015)
We provide experimental evidence of quantum features in bipartite states classified as entirely classical according to a conventional criterion based on the Glauber P function but possessing nonzero Gaussian quantum discord. Their quantum nature is experimentally revealed by acting locally on one part of the discordant state. We experimentally verify and investigate the effect of discord increase under the action of local loss and link it to the entanglement with the environment. Adding an environmental system purifying the state, we unveil the flow of quantum correlations within a global pure system using the Koashi-Winter inequality. For a discordant state generated by splitting a state in which the initial squeezing is destroyed by random displacements, we demonstrate the recovery of entanglement highlighting the role of system-environment correlations.
CRIS-Team Scopus Importer:2022-06-05

Quantumness beyond entanglement: The case of symmetric states - Goldberg, Aaron Z.; Grassl, Markus; Leuchs, Gerd; Sánchez-Soto, Luis L. (Physical Review A, 2022)
Nowadays, it is accepted that truly quantum correlations can exist even in the absence of entanglement. For the case of symmetric states, a physically trivial unitary transformation can alter a state from entangled to separable, and vice versa. We propose to certify the presence of quantumness via an average of a state's bipartite entanglement properties over all physically relevant modal decompositions. We investigate extremal states for such a measure: SU(2)-coherent states possess the least quantumness, whereas the opposite extreme is inhabited by states with maximally spread Majorana constellations.
CRIS-Team Scopus Importer:2022-03-18

Quantum Non-Demolition Measurements with Solitons - Leuchs, Gerd; et al. (Applied Physics B-Lasers and Optics, 1997)
The optical Kerr effect provides an ideal quantum non-demolition interaction. Experiments and proposals using this interaction are reviewed with special emphasis on optical soliton pulses propagating in fibres. The performance of a quantum non-demolition experiment using the optical Kerr effect may be reduced by self-phase modulation of the probe pulse. Proposals to overcome this limitation are discussed.
UnivIS-Import:2015-03-05:Pub.1997.nat.dphy.optik.1optik.quantu_1

Quantum physics in space - Belenchia, Alessio; Carlesso, Matteo; Bayraktar, Ömer; Dequal, Daniele; Derkach, Ivan; Gasbarri, Giulio; Herr, Waldemar; Li, Ying Lia; Rademacher, Markus; Sidhu, Jasminder; Oi, Daniel K.L.; Seidel, Stephan T.; et al. (Physics Reports-Review Section of Physics Letters, 2022)
Advances in quantum technologies are giving rise to a revolution in the way fundamental physics questions are explored at the empirical level. At the same time, they are the seeds for future disruptive technological applications of quantum physics. Remarkably, a space-based environment may open many new avenues for exploring and employing quantum physics and technologies. Recently, space missions employing quantum technologies for fundamental or applied studies have been proposed and implemented with stunning results. The combination of quantum physics and its space application is the focus of this review: we cover both the fundamental scientific questions that can be tackled with quantum technologies in space and the possible implementation of these technologies for a variety of academic and commercial purposes.
CRIS-Team Scopus Importer:2022-01-14
Keywords: Quantum physics; Quantum technology; Space

Quantum polarization tomography of bright squeezed light - Mueller, C. R.; Stoklasa, B.; Peuntinger, Christian; Gabriel, C.; Rehacek, Jaroslav; Hradil, Zdenek; Klimov, A. B.; Leuchs, Gerd; Marquardt, Christoph; Sanchez-Soto, L. L. (New Journal of Physics, 2012)
We reconstruct the polarization sector of a bright polarization squeezed beam starting from a complete set of Stokes measurements. Given the symmetry that underlies the polarization structure of quantum fields, we use the unique SU(2) Wigner distribution to represent states. In the limit of localized bright states, the Wigner function can be approximated by an inverse threedimensional Radon transform. We compare this direct reconstruction with the results of a maximum likelihood estimation, thus finding excellent agreement. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
CRIS-Team Scopus Importer:2022-06-05

Quantum random numbers based on the vacuum state - Gabriel, C.; Wittmann, C.; Sych, D.; Dong, R.; Mauerer, W.; Andersen, U. L.; Marquardt, Christoph; Leuchs, Gerd (Optics InfoBase Conference Papers, 2011)
CRIS-Team Scopus Importer:2022-06-05

Quantum reconstruction of an intense polarization squeezed optical state - Marquardt, Christoph; Heersink, Joel; Dong, Ruifang; Chekova, Maria; Klimov, Andrei B.; Sanchez-Soto, L. L.; Andersen, Ulrik L.; Leuchs, Gerd (Physical Review Letters, 2007)
We perform a reconstruction of the polarization sector of the density matrix of an intense polarization squeezed beam starting from a complete set of Stokes measurements. By using an appropriate quasidistribution, we map this onto the Poincaré space, providing a full quantum mechanical characterization of the measured polarization stat
UnivIS-Import:2015-03-09:Pub.2007.nat.dphy.optik.1optik.quantu_3

Quantum Simulations with Microwave Radiation - Eichler, Christopher (67th Fujihara seminar, 2014)
Keywords: wwwqudev

Quantum Solitons in Fibers - Recent Experimental Progress and Perspectives - Leuchs, Gerd; et al. (Proc. of the Sixth International Conference on Sqeezed States and Uncertainty Relations, 1999)
UnivIS-Import:2015-04-16:Pub.1999.nat.dphy.optik.1optik.quantu_4

Quantum Solitons in Fibres - Internal Structure,Entanglement, and Cats - Leuchs, Gerd; et al. (Proc. of the International Conference on Squeezed States and Uncertainty Relations, 1999)
UnivIS-Import:2015-04-16:Pub.1999.nat.dphy.optik.1optik.quantu

Quantum Solitons in Optical Fibres: Basic Requisites for Experimental Quantum Communication - Leuchs, Gerd; et al. (Quantum Information Theory with Continuous Variables, 2003)
UnivIS-Import:2015-04-20:Pub.2003.nat.dphy.optik.1optik.quantu_3

Quantum State Reconstruction of an Intense Polarization Squeezed State - Marquardt, Christoph; Heersink, Joel; Chekhova, Maria V.; Klimov, A. B.; Sánchez-Soto, Luis L.; Andersen, Ulrik Lund; Leuchs, Gerd (Quantum Electronics and Laser Science Conference 2006, 2006)
The first quantum reconstruction of an intense Kerr squeezed state is reported. Taking into account the algebraic properties of the Stokes operators, the Wigner function describing a polarization squeezed state can also be fully reconstructed.<br

Quantum structure of fiber solitons and quantum communication - Leuchs, Gerd; et al. (Quantum Information Processing, 2003)
UnivIS-Import:2015-04-20:Pub.2003.nat.dphy.optik.1optik.quantu_7

Quantum technologies in space - Kaltenbaek, Rainer; Acin, Antonio; Bacsardi, Laszlo; Bianco, Paolo; Bouyer, Philippe; Diamanti, Eleni; Marquardt, Christoph; Omar, Yasser; Pruneri, Valerio; Rasel, Ernst Maria; Sang, Bernhard; Seidel, Stephan T.; et al. (Experimental Astronomy, 2021)
Recently, the European Commission supported by many European countries has announced large investments towards the commercialization of quantum technology (QT) to address and mitigate some of the biggest challenges facing today's digital era - e.g. secure communication and computing power. For more than two decades the QT community has been working on the development of QTs, which promise landmark breakthroughs leading to commercialization in various areas. The ambitious goals of the QT community and expectations of EU authorities cannot be met solely by individual initiatives of single countries, and therefore, require a combined European effort of large and unprecedented dimensions comparable only to the Galileo or Copernicus programs. Strong international competition calls for a coordinated European effort towards the development of QT in and for space, including research and development of technology in the areas of communication and sensing. Here, we aim at summarizing the state of the art in the development of quantum technologies which have an impact in the field of space applications. Our goal is to outline a complete framework for the design, development, implementation, and exploitation of quantum technology in space.<br
Keywords: Quantum technology; Entanglement; Fundamental tests; Quantum communication; Quantum sensing

Quantum uncertainty in the beam width for optical spatial modes - Chille, Vanessa; Aiello, Andrea; Banzer, Peter; Leuchs, Gerd; Marquardt, Christoph; Treps, Nicolas; Fabre, Claude (2016 Conference on Lasers and Electro-Optics, CLEO 2016, 2016)
We theoretically investigate the quantum uncertainty in the width of optical beams. Many optical applications such as imaging and beam focusing are limited by the quantum noise in spatial characteristics of light beams.
CRIS-Team Scopus Importer:2022-06-05

Quantum uncertainty in the beam width of spatial optical modes - Chille, Vanessa; Banzer, Peter; Aiello, Andrea; Leuchs, Gerd; Marquardt, Christoph; Treps, Nicolas; Fabre, Claude (Optics Express, 2015)
We theoretically investigate the quantum uncertainty in the beam width of transverse optical modes and, for this purpose, define a corresponding quantum operator. Single mode states are studied as well as multimode states with small quantum noise. General relations are derived, and specific examples of different modes and quantum states are examined. For the multimode case, we show that the quantum uncertainty in the beam width can be completely attributed to the amplitude quadrature uncertainty of one specific mode, which is uniquely determined by the field under investigation. This discovery provides us with a strategy for the reduction of the beam width noise by an appropriate choice of the quantum state.
CRIS-Team Scopus Importer:2022-06-05

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

Quasi-absolute measurement of aspheres with a combined diffractive optical element as reference. - Lindlein, Norbert; et al. (Applied Optics, 2006)
We have already reported a method for the quasi-absolute test of rotationally symmetric aspheres by means of combined diffractive optical elements (combo-DOEs). The combo-DOEs carry the information for the ideal shape of an aspheric surface under test as well as a spherical wave for the measurement at the cat's eye position. An experimental demonstration of the procedure is given. Measurements with two different designs of combo-DOEs have been conducted, and their relative advantages and disadvantages are discussed.

QUBE-II - Quantum Key Distribution with a CubeSat - Hutterer, Martin; Auer, Michael; Baliuka, Adomas; Bayraktar, Ömer; Freiwang, Peter; Gall, Marcell; Günthner, Kevin; Haber, Roland; Janusch, Janko; Knips, Lukas; Kobel, Pascal; Krauss, Markus; et al. (IAC-22-B4.9-GTS.5.5,x70823, 2022)
Keywords: QKD; CubeSat; QUBE; Quantum Payload; Quantum Mechanics; QRNG

QUBE – Towards Quantum Key Distribution with Small Satellites - Knips, Lukas; Auer, Michael; Baliuka, Adomas; Bayraktar, Ömer; Freiwang, Peter; Grünefeld, Matthias; Haber, Roland; Lemke, Norbert; Marquardt, Christoph; Moll, Florian; Pudelko, Jonas; Rödiger, Benjamin; et al. (Optics InfoBase Conference Papers, 2022)
Quantum Key Distribution (QKD) in space will be integral for future quan-tum networks. The space mission QUBE will test novel integrated optics components in a three-unit CubeSat demonstrating an economic route for global-scale QKD.
CRIS-Team Scopus Importer:2022-09-02

Qubit-Photon Entanglement and Hong-Ou-Mandel Interference with Propagating Microwaves - Eichler, Christopher; et al. (APS March Meeting, 2013)
Keywords: wwwqudev

Raman-Free, Noble-Gas-Filled Photonic-Crystal Fiber Source for Ultrafast, Very Bright Twin-Beam Squeezed Vacuum - Finger, Martin A.; Iskhakov, Timur Sh.; Joly, Nicolas; Chekhova, Maria; Russell, Philip St. John (Physical Review Letters, 2015)
We report a novel source of twin beams based on modulational instability in high-pressure argon-filled hollow-core kagome-style photonic-crystal fiber. The source is Raman-free and manifests strong photonnumber correlations for femtosecond pulses of squeezed vacuum with a record brightness of similar to 2500 photons per mode. The ultra-broadband (similar to 50 THz) twin beams are frequency tunable and contain one spatial and less than 5 frequency modes. The presented source outperforms all previously reported squeezed-vacuum twin-beam sources in terms of brightness and low mode content.

Raman frequency conversion between guided vortex modes in twisted gas-filled photonic crystal fibers - Davtyan, Sona; Novoa, David; Chen, Yang; Frosz, Michael H.; Russell, Philip St. John (Optics InfoBase Conference Papers, 2020)
We report efficient Raman conversion of vortex modes in twisted hydrogen-filled hollow-core photonic crystal fibers. Circular birefringence provides topological protection and broadband guidance of helically-phased modes over long distances.
CRIS-Team Scopus Importer:2020-11-13

Range Sensing of the first, the second, and the third kind - Häusler, Gerd (Proc. of the EOS Topical Meetings Digest Series, 1994)
UnivIS-Import:2015-04-16:Pub.1994.nat.dphy.optik.1optik.ranges

Rapid and accurate calculation of vector photonic band-structure in regular arrays of coupled waveguides - Chen, Yang; Russell, Philip St. John (2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2019, 2019)
Vector coupled-mode (VCM) theory, applied to helical Bloch waves [1], was recently introduced to clarify the origins of circular dichroism in twisted single-ring hollow-core photonic crystal fibres [2]. Here we show it can also be used to calculate, rapidly and precisely, the photonic band structure of regular lattices of coupled anisotropic waveguides, offering considerable advantages over the plane-wave expansion method and finite element modelling (FEM). As an example, we treat a graphene-like lattice of coupled cores (Fig. 1a), which represents the type of mode seen in coreless twisted PCF [3]. The VCM approach itself is illustrated in Fig. 1b.
CRIS-Team Scopus Importer:2019-11-15

Rapid prototyping of 1xN multifocus gratings via additive direct laser writing - Reischke, Marie; Vanderpoorten, Oliver; Ströhl, Florian (Micro and Nano Engineering, 2023)
Multifocus gratings (MFGs) enable microscopes and other imaging systems to record entire Z-stacks of images in a single camera exposure. The exact grating shape depends on microscope parameters like wavelength and magnification and defines the multiplexing onto a grid of MxN Z-slices. To facilitate the swift production and alteration of MFGs for a system and application at hand, we have developed a fabrication protocol that allows manufacturing of 1xN MFGs within hours and without the requirement of clean room facilities or hazardous etching steps. Our approach uses photolithography with a custom-built stage-scanning direct laser writing (DLW) system. By writing MFG grating lines into spin-coated negative tone SU-8 photoresist, polymerized parts are crafted onto the substrate and thus directly become a part of the grating structure. We provide software to generate the required MFG grating line paths, details of the DLW system and fully characterize a manufactured MFG. Our produced MFG is 5.4 mm in diameter and manages to record an image volume with a Z-span of over 600 μm without spherical aberrations or noticeable loss of resolution.
CRIS-Team Scopus Importer:2023-04-28
Keywords: 3D microscopy; Additive manufacturing; Diffraction grating; Direct laser writing; Photolithography; SU-8; Two-photon

Rauschunterdrückung und Pulsformung in faseroptischen Sagnac Interferometern (NOLM) - Wietfeld, André; Schmauß, Bernhard; Meißner, Markus; Leuchs, Gerd (ITG Workshop Modellierung photonischer Komponenten und Systeme, Stuttgart, November, 2001)
UnivIS-Import:2015-04-16:Pub.2001.tech.IE.LEH.rausch_7

Rauschunterdrückung und Pulsformung mit einem Faser Sagnac Interferometer - Wietfeld, André; Meißner, Markus; Schmauß, Bernhard (Workshop der ITG Fachgruppe 5.3.1., 2001)
UnivIS-Import:2015-04-16:Pub.2001.tech.IE.LEH.rausch

Rayleigh-Backscattering Impact on Performance of NOLM-Based Phase-Preserving Optical Limiters - Onishchukov, G.; Sponsel, K.; Stephan, C.; Roethlingshoefer, T.; Schmauß, Bernhard; Leuchs, Gerd (Photonics Society Summer Topical Meetings Series, IEEE, 2010)
lhft_intern.bib::Onishchukov10

Reaktionen des zwitterionischen Thiooxalsäure-2-amid-1-hydrazid-2-hydrazons - Dehne, Henry; Scheunemann, A.; Michalik, M.; Hartung, H.; Heinemann, Frank Wilhelm (Sulfur Letters, 1995)

Realization of two-qubit gates with tunable couplers in superconducting circuits - Eichler, Christopher; et al. (APS March Meeting, 2019)
Keywords: wwwqudev

Realizing a reinforcement learning agent for real-time quantum feedback - Eichler, Christopher (ENS Lyon, seminar hosted by Benjamin Huard, 2022)
Rapid advancements in building quantum information processing devices at scale call for radical paradigm shifts in the real-time control of quantum systems. Reinforcement learning offers a powerful approach to learn sophisticated control strategies in the absence of detailed models and promises to become a game changer in quantum technology as it did in many other disciplines ranging from board games, to robotics, to fundamental science. In my talk, I will show how we achieve real-time feedback control of a quantum system by using a reinforcement learning agent. We realize the agent as a novel low-latency neural-network on a field-programmable gate array interacting with a superconducting quantum system at MHz rates, which is more than 100 times faster than any other previous implementation of a reinforcement learning agent deployed in any physics experiment. Our work paves the way towards using reinforcement learning for real-time control of quantum computers, most notably for quantum error correction and fault-tolerant gate operations. Beyond that, the unprecedented speed of the agent marks an important engineering achievement , which can be deployed in a wide range of other applications, such as real-time the control of optical systems.
Keywords: wwwquantum

Realizing Quantum Convolutional Neural Networks on a Superconducting Quantum Processor - Eichler, Christopher (International Quantum Tensor Network, 2022)
Keywords: wwwqudev

Realizing Quantum Convolutional Neural Networks on a Superconducting Quantum Processor - Eichler, Christopher (Seminar, Quantum Theory Group, 2022)
Keywords: wwwqudev

Recent experimental results and future directions of the DLA single grating project - McNeur, Joshua; Hammer, Jonas; Li, Ang; Tafel, Alexander; Hommelhoff, Peter; Tafel, Alexander; Hammer, Jakob (16th Advanced Accelerator Concepts Workshop, AAC 2014, 2016)
The recent demonstration of Dielectric Laser Acceleration of subrelativistic electrons is reviewed. In this experiment, a Ti:Sapphire laser is incident upon a fused silica grating, exciting fields that accelerated 28 keV electrons with a 25 MeV/m acceleration gradient. Upgrades and future directions of this DLA project are discussed.

Reconstructing two-dimensional spatial modes for classical and quantum light - Averchenko, Valentin A.; Frascella, Gaetano; Kalash, Mahmoud; Cavanna, Andrea; Chekhova, Maria (Physical Review A, 2020)
We propose a method for finding two-dimensional spatial modes of thermal field through a direct measurement of the field intensity and an offline analysis of its spatial fluctuations. Using this method, in a simple and efficient way we reconstruct the modes of a multimode fiber and the spatial Schmidt modes of squeezed vacuum generated via high-gain parametric down-conversion. The reconstructed shapes agree with the theoretical results.
CRIS-Team WoS Importer:2020-12-18

Reconstruction of guided helical bloch modes in twisted coreless photonic crystal fibre using bessel beams - Roth, P.; Wong, G. K.L.; Frosz, Michael H.; Ahmed, G.; Russell, Philip St. John (2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2019, 2019)
Light beams carrying orbital angular momentum (OAM) are of fundamental interest in many fields of research [1]. Recently it has been reported that helical Bloch modes (HBMs) carrying multiple values of OAM are guided in chirally twisted photonic crystal fibre (PCF), even when there is no core [2]. HBMs are not supported by conventional waveguides and would be very difficult to realise using multi-beam interference. Here we report the first complete experimental characterisation of the phase and amplitude of the complex HBM fields in twisted coreless PCF. We compare the measurements with finite element simulations, based on precise scanning electron micrographs of the fibre structure, obtaining excellent agreement. We then expand the numerically calculated HBM fields as a series of Bessel beams, allowing us to calculate the strengths and azimuthal orders of the HBM harmonics with a fidelity greater than 95%.
CRIS-Team Scopus Importer:2019-11-15

Reconstruction of smoothed polyhedral surfaces from multiple range images - Häusler, Gerd; et al. (3D Image Analysis and Synthesis '97, 1997)
UnivIS-Import:2015-04-20:Pub.1997.nat.dphy.optik.1optik.recons

Reducing losses in solid-core photonic crystal fibers using chlorine dehydration - Frosz, Michael H.; Ahmed, Goran; Lapshina, Nadezda; Keding, Ralf; Babic, Fehim; Joly, Nicolas; Russell, Philip St. John (Optical Materials Express, 2016)
The fabrication of photonic crystal fibers (PCFs) involves the stacking of multiple preform elements, providing many opportunities for contamination by water vapor or dust particles and causing increased fiber loss. Even after manufacture, diffusion of water vapor into the hollow channels is known to cause a slow increase in loss if the fibers are stored in a humid environment. In this paper we report a systematic study of three methods to reduce OH-related loss in solid-core PCFs: (1) treating the stack (primary preform) with chlorine or oxygen; (2) treating the cane (intermediate preform) with chlorine or oxygen; and (3) using a dry gas for pressurization of the hollow channels during the final step of fiber drawing. Each treatment is independently found effective in reducing OH-related loss, although stack treatment alone is not sufficient if the canes are subsequently stored for a longer time. On the other hand, chlorine-treatment of the canes and/ or using a suitably dry gas using fiber drawing significantly lowers the loss even when the canes have been stored for more than two years in a closed tube at room temperature and at relative humidities in the range similar to 20% to similar to 50%. (C) 2016 Optical Society of America

Reduction of guided acoustic wave brillouin scattering in photonic crystal fibers - Elser, Dominique Alexander; Andersen, Ulrik Lund; Korn, Alexander; Glöckl, Oliver; Lorenz, Stefan; Marquardt, Christoph; Leuchs, Gerd (Physical Review Letters, 2006)
Guided acoustic wave Brillouin scattering (GAWBS) generates phase and polarization noise of light propagating in glass fibers. This excess noise affects the performance of various experiments operating at the quantum noise limit. We experimentally demonstrate the reduction of GAWBS noise in a photonic crystal fiber in a broad frequency range by tailoring the acoustic modes using the photonic also as a phononic crystal. We compare the noise spectrum to the one of a standard fiber and observe a tenfold noise reduction in the frequency range up to 200 MHz. Based on our measurement results as well as on numerical simulations, we establish a model for the reduction of GAWBS noise in photonic crystal fibers. © 2006 The American Physical Society.
Created from Fastlane, Scopus look-up

Reduction of Nonlinear Phase Noise in DPSK Transmission Using a NALM - Stephan, Christian; Sponsel, Klaus; Onishchukov, Georgy; Schmauß, Bernhard; Leuchs, Gerd (IEEE/LEOS Winter Topicals Meeting Series, 2009)
Performance of a NALM as phase-preserving amplitude 2R-regenerator in a DPSK transmission system has been investigated experimentally and numerically. A 3dB improvement of eye opening or alternatively a 3dB increase of fibre-launched power are demonstrated.
UnivIS-Import:2017-12-18:Pub.2009.tech.IE.LEH.reduct

Reduction of phase singularities in speckle-shearing interferometry by incoherent averaging of speckle patterns - Mantel, K.; Nercissian, Vanusch; Lindlein, Norbert (Optical Measurement Systems for Industrial Inspection IX, 2015)
Speckle interferometry is a well established technique for the optical characterization of rough objects, with the quantification of deformations as one particular application of interest. Owing to its common path property, a speckle-shearing interferometer is often the natural choice as a setup. Like other speckle techniques, however, speckle-shearing interferometry suffers from the existence of phase singularities present in the speckle patterns. Phase singularities introduce ambiguities into the phase unwrapping process and make this evaluation step highly sophisticated. In this work, we attempt to reduce the number of phase singularities by physical means, i. e. by applying an incoherent averaging of multiple, mutually independent speckle intensities. The effect of the incoherent averaging on the number of phase singularities has been investigated theoretically, by computer simulations, and experimentally. To obtain high contrast fringes in connection with a shearing setup, which would not be the case for a simple extended light source, a periodically structured light source with a period matched to the shear distance is applied. It turns out that the number of phase singularities may indeed be reduced, but only to a certain extent.
Keywords: incoherent averaging; phase singularities; Speckle-shearing interferometry

Reduction of the focal spot size by using polarization effects - Leuchs, Gerd; et al. (IQEC'2000 Conference Digest, 2000)
Polarization distribution of the focused beam reduced the focal area in an optical system with high numerical aperture (NA). Focal intensity distribution was measured using knife edge method setup. An incoming beam is focused by a microscope objective onto a specially designed p-i-n photodiode, where parts of the light sensitive area were covered with a sharp edged gold pad. By measuring the dependence of the photocurrent on the translation distance for different translation directions and orientations of the gold pad a reconstruction of the shape of the focus is possible by applying the Radon back-transformation.
UnivIS-Import:2015-04-16:Pub.2000.nat.dphy.optik.1optik.reduct_8

Reduction of the Rayleigh-Backscattering Impact in Nonlinear Loop Mirrors by Dispersion Management - Röthlingshöfer, Tobias; Sponsel, Klaus; Onishchukov, Georgy; Schmauß, Bernhard; Leuchs, Gerd (OSA Conference on Nonlinear Photonic, 2010)
UnivIS-Import:2016-06-01:Pub.2011.tech.IE.LEH.reduct

Reduktion der Residuenanzahl bei lateraler Speckle-Shearing-Interferometrie: Simulationen und Messergebnisse - Nercissian, Vanusch; Mantel, Klaus Peter; Harder, Irina; Lindlein, Norbert (115. Jahrestagung der DGaO, 2014)

Reduktion von Phasensingularitäten bei lateraler Shearing-Speckle-Interferometrie - Nercissian, Vanusch; Mantel, Klaus Peter; Seifert, Kristina Johanna; Berger, Andreas; Harder, Irina; Lindlein, Norbert (114. Jahrestagung der DGaO, 2013)

Refining Triangle Meshes by Non-Linear Subdivision - Häusler, Gerd; et al. (Proceedings of Third International Conference on 3-DDigital Imaging and Modeling, 2001)
UnivIS-Import:2015-04-16:Pub.2001.nat.dphy.optik.1optik.refini

Refraktive Strahlformungsoptik mittels direktschreibender Grautonlithographie - Leroch, Dominik; Harder, Irina; Lindlein, Norbert (114. Jahrestagung der DGaO, 2013)

Reliable simulation of optical bridge system by exchanging optical field data - Lindlein, Norbert; et al. (Photon Management III, 2008)
In succession of a benchmark study for the modeling of micro-optical components in the Network of Excellence on Micro-Optics (NEMO) we define a novel systematic approach for the evaluation of modeling results and the combination of different modeling approaches and modeling expertise. The method is applied for an optical bridge system, comprising both refractive and diffractive optical components. We work with different intermediate planes at which the field distributions obtained with different simulation tools are rigorously compared. Therefore all participating partners have programmed the necessary tools that allow the exchange of obtained field distributions. First evaluation results are discussed in detail.
Keywords: Diffractive element; Micro-lens; Modeling; Optical field data

Repeated Quantum Error Correction in a Surface Code Using Superconducting Circuits - Eichler, Christopher (IST Austria : Vienna, Austria, 2022)
The ability to perform logical quantum operations fault-tolerantly by correcting unavoidable errors induced by control inaccuracies and decoherence, will be essential for building and operating large-scale quantum computers. In my talk, I present our recent demonstration of repeated quantum error correction using a surface code, which is known for it exceptionally high error threshold and its compatibility with planar qubit architectures featuring nearest-neighbor coupling. The code implemented in our experiments uses 17 physical qubits, nine of of which encode the logical information and eight of which perform repeated measurements of error syndromes. By decoding the syndrome data in post-processing we preserve initialized logical states with a low error probability of 3% per cycle. The demonstration of repeated, fast and high-performance quantum error correction supports our understanding that fault-tolerant quantum computation will eventually be realizable. [1] S. Krinner, N. Lacroix, A. Remm, A. Di Paolo, E. Genois, C. Leroux, C. Hellings, S. Lazar, F. Swiadek, J. Herrmann, G. J. Norris, C K. Andersen, M. Müller, A. Blais, C. Eichler, and A. Wallraff, arxiv.org:2112.03708 (2021)
Keywords: wwwqudev

Repeated Quantum Error Correction in a Surface Code Using Superconducting Circuits - Eichler, Christopher (CMD 29, Superconducting Circuits for Quantum Technologies, 2022)
The ability to perform logical quantum operations fault-tolerantly by correcting unavoidable errors induced by control inaccuracies and decoherence, will be essential for building and operating large-scale quantum computers. In my talk, I present our recent demonstration of repeated quantum error correction using a surface code, which is known for it exceptionally high error threshold and its compatibility with planar qubit architectures featuring nearest-neighbor coupling. The code implemented in our experiments uses 17 physical qubits, nine of of which encode the logical information and eight of which perform repeated measurements of error syndromes. By decoding the syndrome data in post-processing we preserve initialized logical states with a low error probability of 3% per cycle. The demonstration of repeated, fast and high-performance quantum error correction supports our understanding that fault-tolerant quantum computation will eventually be realizable.
Keywords: wwwqudev

Repeated Quantum Error Correction in a Surface Code Using Superconducting Circuits - Eichler, Christopher (Physics Frontiers with Quantum Science and Technology, 2022)
Keywords: wwwqudev

Repeated Quantum Error Correction in a Surface Code Using Superconducting Circuits - Eichler, Christopher (Walter-Meissner-Institut, 2022)
The ability to perform logical quantum operations fault-tolerantly by correcting unavoidable errors induced by control inaccuracies and decoherence, will be essential for building and operating large-scale quantum computers. In my talk, I present our recent demonstration of repeated quantum error correction using a surface code [1], which is known for it exceptionally high error threshold and its compatibility with planar qubit architectures featuring nearest-neighbor coupling. The code implemented in our experiments uses 17 physical qubits, nine of of which encode the logical information and eight of which perform repeatedmeasurements of error syndromes. By decoding the syndrome data in post-processing we preserve initialized logical states with a low error probability of 3% per cycle. The demonstration of repeated, fast and high-performance quantum error correction supports our understanding that fault-tolerant quantum computation will eventually be realizable. [1] S. Krinner, N. Lacroix, A. Remm, A. Di Paolo, E. Genois, C. Leroux, C. Hellings, S. Lazar, F. Swiadek, J. Herrmann, G. J. Norris, C K. Andersen, M. Müller, A. Blais, C. Eichler, and A. Wallraff, arxiv.org:2112.03708 (202
Keywords: wwwqudev

Resonance amplification of defect emission in ZnO-inverted opal - Khunsin, Worawut; Scharrer, Michael; Aagesen, Larry K.; Anderson, Mark A.; Chang, Robert P. H.; Sotomayor Torres, Clivia M.; Romanov, Sergei G. (Optics Letters, 2009)
Transformation of broadband emission of oxygen defects in the carcass of ZnO-inverted opal into a multiple-mode amplified spontaneous emission band has been observed in the spectral interval of a photonic bandgap upon increasing excitation intensity. The mode structure has been assigned to amplification of emission coupled to resonance modes of the self-selected distributed Bragg resonator. The surprisingly low 2 W/cm^2 onset of amplification has been explained by the long radiative decay time of defect states populated according to the three-level excitation scheme. The decrease of emission intensity between amplified peaks has been associated with the saturation of the ZnO defect emission.
EAM Import::2019-03-13

Resonant electro-optic frequency comb - Rueda, Alfredo; Sedlmeir, Florian; Kumari, Madhuri; Leuchs, Gerd; Schwefel, Harald G. L. (Nature, 2019)
High-speed optical telecommunication is enabled by wavelength-division multiplexing, whereby hundreds of individually stabilized lasers encode information within a single-mode optical fibre. Higher bandwidths require higher total optical power, but the power sent into the fibre is limited by optical nonlinearities within the fibre, and energy consumption by the light sources starts to become a substantial cost factor 1 . Optical frequency combs have been suggested to remedy this problem by generating numerous discrete, equidistant laser lines within a monolithic device; however, at present their stability and coherence allow them to operate only within small parameter ranges 2–4 . Here we show that a broadband frequency comb realized through the electro-optic effect within a high-quality whispering-gallery-mode resonator can operate at low microwave and optical powers. Unlike the usual third-order Kerr nonlinear optical frequency combs, our combs rely on the second-order nonlinear effect, which is much more efficient. Our result uses a fixed microwave signal that is mixed with an optical-pump signal to generate a coherent frequency comb with a precisely determined carrier separation. The resonant enhancement enables us to work with microwave powers that are three orders of magnitude lower than those in commercially available devices. We emphasize the practical relevance of our results to high rates of data communication. To circumvent the limitations imposed by nonlinear effects in optical communication fibres, one has to solve two problems: to provide a compact and fully integrated, yet high-quality and coherent, frequency comb generator; and to calculate nonlinear signal propagation in real time 5 . We report a solution to the first problem.
CRIS-Team Scopus Importer:2019-05-02

Resonant electro-optic frequency comb generation in lithium niobate disk resonator inside a microwave cavity - Rueda, Alfredo; Sedlmeir, Florian; Leuchs, Gerd; Kumari, Madhuri; Schwefel, Harald (Optics InfoBase Conference Papers, 2019)
We demonstrate electro-optic frequency comb generation using a doubly resonant system comprising a whispering gallery mode disk resonator made of lithium niobate mounted inside a three dimensional copper cavity. We observe 180 sidebands centred at 1550 nm.
CRIS-Team Scopus Importer:2020-02-21

Resonant metamaterials for contrast enhancement in optical lithography - Dobmann, Sabine; Shyroki, Dzmitry; Banzer, Peter; Erdmann, Andreas; Peschel, Ulf (Optics Express, 2012)
The transmission through ultra-thin metal films is noticeable and thus limits their potential for the formation of lithographic masks. By sub-wavelength patterning of a metal film with a post structure, a resonant metamaterial is formed, which can effectively suppress the transmission. Measurements as well as calculations identify the width of the metal islands as a critical geometrical feature. Hence, the extraordinarily low transmission effect can be explained by the resonant response of single scatterers known as Localized Surface Plasmon Resonances (LSPR). A potential application of this suppressed transmission effect to thin metal masks in optical lithography is experimentally investigated.
EAM Import::2019-03-13

Resonant metasurfaces for generating complex quantum states - Santiago Cruz, Tomás; Gennaro, Sylvain D.; Mitrofanov, Oleg; Addamane, Sadhvikas; Reno, John; Brener, Igal; Chekhova, Maria (Science, 2022)
Quantum state engineering, the cornerstone of quantum photonic technologies, mainly relies on spontaneous parametric downconversion and four-wave mixing, where one or two pump photons spontaneously decay into a photon pair. Both of these nonlinear effects require momentum conservation for the participating photons, which strongly limits the versatility of the resulting quantum states. Nonlinear metasurfaces have subwavelength thickness and allow the relaxation of this constraint; when combined with resonances, they greatly expand the possibilities of quantum state engineering. Here, we generated entangled photons via spontaneous parametric downconversion in semiconductor metasurfaces with high-quality factor, quasi-bound state in the continuum resonances. By enhancing the quantum vacuum field, our metasurfaces boost the emission of nondegenerate entangled photons within multiple narrow resonance bands and over a wide spectral range. A single resonance or several resonances in the same sample, pumped at multiple wavelengths, can generate multifrequency quantum states, including cluster states. These features reveal metasurfaces as versatile sources of complex states for quantum information.
CRIS-Team Scopus Importer:2022-09-09

Resonant photo-ionization of Yb+ to Yb2+ - Heugel, Simon Tobias; Fischer, Martin; Elman, Vladimir; Maiwald, Robert; Sondermann, Markus; Leuchs, Gerd (Journal of Physics B: Atomic, Molecular and Optical Physics, 2016)
We demonstrate the controlled creation of a Yb ion by photo-ionizing Yb with weak continuous-wave lasers at ultraviolet wavelengths. The photo-ionization is performed by resonantly exciting transitions of the Yb ion in three steps. Starting from an ion crystal of two laser-cooled Yb ions localized in a radio-frequency trap, the verification of the ionization process is performed by characterizing the properties of the resulting mixed-species ion-crystal. The obtained results facilitate fundamental studies of physics involving Yb ions.
Keywords: light-matter interaction; photo-ionization; ytterbium

Reverse Engineering mit Hilfe optischer 3D-Sensoren - Häusler, Gerd; et al. (Optische 3D-Erfassung großer Objekte, 1996)
UnivIS-Import:2015-04-16:Pub.1996.nat.dphy.optik.1optik.revers

Reverse engineering using optical 3D sensors - Häusler, Gerd; et al. (Proceedings of SPIE, 1998)
Optical 3D sensors are used as tools for reverse engineering: First the shape of an object is digitized by acquisition of multiple range images from different view points. Then the range images are registered and the data is turned into a CAD description, e.g. tensor product surfaces, by surface modeling software. For many applications however it is sufficient to generate a polyhedral surface. We present a nearly automatic procedure covering the complete task of data acquisition, calibration, surface registration and surface reconstruction using a mesh of triangles. A couple of measurements, such as teeth, works of art and cutting tools are shown.
UnivIS-Import:2015-03-05:Pub.1998.nat.dphy.optik.1optik.revers
Keywords: 3D sensing; Calibration; Optical 3D sensor; Registration; Reverse engineering; Surface reconstruction; Triangulation

Reverse Engineering using Optical Range Sensors - Häusler, Gerd; et al. (Handbook of Computer Vision and Applications Vol. 3: Systems and Applications, 1999)
UnivIS-Import:2015-04-20:Pub.1999.nat.dphy.optik.1optik.revers

Ring-shaped molecules as split ring resonators of a molecular metamaterial - Lindlein, Norbert; et al. (Photonic Metamaterials: From Random to Periodic, META 2006, 2006)
We analytically analyse the magnetic response of ring shaped molecules. We find that circular symmetry must be broken and that transitions between higher order states have to be enabled to ob-tain a reasonable magnetic response. © 2006 Optical Society of America.

Risk analysis of Trojan-horse attacks on practical quantum key distribution systems - Jain, Nitin; Stiller, Birgit; Khan, Imran; Makarov, Vadim; Marquardt, Christoph; Leuchs, Gerd (IEEE Journal of Selected Topics in Quantum Electronics, 2015)
An eavesdropper Eve may probe a quantum key distribution (QKD) system by sending a bright pulse from the quantum channel into the system and analyzing the back-reflected pulses. Such Trojan-horse attacks can breach the security of the QKD system, if appropriate safeguards are not installed or if they can be fooled by the Eve. We present a risk analysis of such attacks based on extensive spectral measurements, such as transmittance, reflectivity, and detection sensitivity of some critical components used in a typical QKD systems. Our results indicate the existence of wavelength regimes, where the attacker gains considerable advantage as compared to launching an attack at 1550 nm. We also propose countermeasures to reduce the risk of such attacks.
CRIS-Team Scopus Importer:2021-06-29
Keywords: Electrooptic modulators; Fiber optics; Infrared detectors; Infrared spectra; Optical pulses; Optical receivers; Photodetectors; Quantum cryptography; Quantum key distribution; Reflectometry; Supercontinuum; Transmittance; Trojan-horse attack

Route from single-pulse to multi-pulse states in a mid-infrared soliton fiber laser - Huang, J.; Pang, M.; Jiang, X.; He, W.; Russell, Philip St. John (Optics Express, 2019)
State-of-the-art ultrafast mid-IR fiber lasers deliver optical solitons with durations of several hundred femtoseconds. The Er- or Ho-doped fluoride gain fibers generally used in these lasers have strong anomalous dispersion at ∼3 µm, which generally forces them to operate in the soliton regime. Here we report that a pulse-energy clamping effect, caused by the buildup of intracavity nonlinearities, limits the shortest obtainable pulse durations in these mid-infrared soliton fiber lasers. Excessive intra-cavity energy results in soliton instability, collapse and fragmentation into a variety of stable multi-pulse states, including phase-locked soliton molecules and harmonically mode-locked states. We report that the spectral evolution of the mid-IR laser pulses can be recorded between roundtrips through stretching their second-harmonic signal in a 25-km-length of single-mode fiber. Using a modified dispersive Fourier transform set-up, we were able to perform for the first time spectro-temporal measurements of mid-IR laser pulses both in the pulsed state and during pulse collapse and fragmentation. The results provide insight into the complex nonlinear dynamics of mid-IR soliton fiber lasers and open up new opportunities for obtaining a variety of stable multi-pulse mode-locked states at mid-IR wavelengths.
CRIS-Team Scopus Importer:2019-09-24

Satellite quantum communication via the alphasat laser communication terminal quantum signals from 36 thousand kilometers above earth - Elser, Dominique Alexander; Günthner, Kevin; Khan, Imran; Stiller, Birgit; Marquardt, Christoph; Leuchs, Gerd; Saucke, Karen; Tröndle, Daniel; Heine, Frank; Seel, Stefan; Greulich, Peter; Zech, Herwig; et al. (2015 IEEE International Conference on Space Optical Systems and Applications, ICSOS 2015, 2016)
By harnessing quantum effects, we nowadays can use encryption that is in principle proven to withstand any conceivable attack. These fascinating quantum features have been implemented in metropolitan quantum networks around the world. In order to interconnect such networks over long distances, optical satellite communication is the method of choice. Standard telecommunication components allow one to efficiently implement quantum communication by measuring field quadratures (continuous variables). This opens the possibility to adapt our Laser Communication Terminals (LCTs) to quantum key distribution (QKD). First satellite measurement campaigns are currently validating our approach.
CRIS-Team Scopus Importer:2021-06-29
Keywords: free-space optical communication; quantum cryptography; quantum key distribution; satellite quantum communication; satellite-ground laser communication

Scaling rules for high quality soliton self-compression in hollow-core fibers - Schade, Daniel; Köttig, Felix; Koehler, Johannes R.; Frosz, Michael H.; Russell, Philip St. John; Tani, Francesco (Optics Express, 2021)
Soliton dynamics can be used to temporally compress laser pulses to few fs durations in many different spectral regions. Here we study analytically, numerically and experimentally the scaling of soliton dynamics in noble gas-filled hollow-core fibers. We identify an optimal parameter region, taking account of higher-order dispersion, photoionization, self-focusing, and modulational instability. Although for single-shots the effects of photoionization can be reduced by using lighter noble gases, they become increasingly important as the repetition rate rises. For the same optical nonlinearity, the higher pressure and longer diffusion times of the lighter gases can considerably enhance the long-term effects of ionization, as a result of pulse-by-pulse buildup of refractive index changes. To illustrate the counter-intuitive nature of these predictions, we compressed 250 fs pulses at 1030 nm in an 80-cm-long hollow-core photonic crystal fiber (core radius 15 µm) to ∼5 fs duration in argon and neon, and found that, although neon performed better at a repetition rate of 1 MHz, stable compression in argon was still possible up to 10 MHz.
CRIS-Team Scopus Importer:2021-06-18

Scattering of an exponential pulse by a single atom - Sondermann, Markus; Leuchs, Gerd (Romanian Reports in Physics, 2013)
We discuss the scattering of a light pulse by a single atom in free space using a purely semi-classical framework. The atom is treated as a linear elastic scatterer allowing to treat each spectral component of the incident pulse separately. For an increasing exponential pulse with a dipole radiation pattern incident from full solid angle the spectrum resulting from interference of incident and scattered components is a decreasing exponential pulse.

Scheme for the generation of entangeled solitons for quantum communication - Leuchs, Gerd; et al. (Journal of Modern Optics, 1999)
UnivIS-Import:2015-03-05:Pub.1999.nat.dphy.optik.1optik.scheme

Search for Correlations of High-energy Neutrinos Detected in IceCube with Radio-bright AGN and Gamma-Ray Emission from Blazars - Abbasi, R.; Ackermann, M.; Adams, J.; Agarwalla, S. K.; Aguilar, J. A.; Ahlers, M.; Alameddine, J. M.; Amin, N. M.; Andeen, K.; Anton, Gisela; Argüelles, C.; Ashida, Y.; et al. (Astrophysical Journal, 2023)
The IceCube Neutrino Observatory sends realtime neutrino alerts with a high probability of being astrophysical in origin. We present a new method to correlate these events and possible candidate sources using 2089 blazars from the Fermi-LAT 4LAC-DR2 catalog and with 3413 active galactic nuclei (AGNs) from the Radio Fundamental Catalog. No statistically significant neutrino emission was found in any of the catalog searches. The result suggests that a small fraction, <1%, of the studied AGNs emit neutrinos that pass the alert criteria, and is compatible with prior evidence for neutrino emission presented by IceCube and other authors from sources such as TXS 0506 + 056 and PKS 1502 + 106. We also present cross-checks to other analyses that claim a significant correlation using similar data samples.
CRIS-Team Scopus Importer:2023-10-20

Search for Galactic Core-collapse Supernovae in a Decade of Data Taken with the IceCube Neutrino Observatory - Abbasi, R.; Ackermann, M.; Adams, J.; Agarwalla, S. K.; Aguilar, J. A.; Ahlers, M.; Alameddine, J. M.; Amin, N. M.; Andeen, K.; Anton, Gisela; Argüelles, C.; Ashida, Y.; et al. (Astrophysical Journal, 2024)
The IceCube Neutrino Observatory has been continuously taking data to search for O(0.5–10) s long neutrino bursts since 2007. Even if a Galactic core-collapse supernova is optically obscured or collapses to a black hole instead of exploding, it will be detectable via the O(10) MeV neutrino burst emitted during the collapse. We discuss a search for such events covering the time between 2008 April 17 and 2019 December 31. Considering the average data taking and analysis uptime of 91.7% after all selection cuts, this is equivalent to 10.735 yr of continuous data taking. In order to test the most conservative neutrino production scenario, the selection cuts were optimized for a model based on an 8.8 solar mass progenitor collapsing to an O–Ne–Mg core. Conservative assumptions on the effects of neutrino oscillations in the exploding star were made. The final selection cut was set to ensure that the probability to detect such a supernova within the Milky Way exceeds 99%. No such neutrino burst was found in the data after performing a blind analysis. Hence, a 90% C.L. upper limit on the rate of core-collapse supernovae out to distances of ≈25 kpc was determined to be 0.23 yr−1. For the more distant Magellanic Clouds, only high neutrino luminosity supernovae will be detectable by IceCube, unless external information on the burst time is available. We determined a model-independent limit by parameterizing the dependence on the neutrino luminosity and the energy spectrum.
CRIS-Team Scopus Importer:2024-02-16
Keywords: Core-collapse supernovae (304); Neutrino telescopes (1105); Supernova neutrinos (1666)

Search for Spatial Correlations of Neutrinos with Ultra-high-energy Cosmic Rays - Albert, A.; Domi, Alba; Alves, S.; Andre, M.; Anghinolfi, M.; Ardid, S.; Aubert, J-J; Aublin, J.; Baret, B.; Basa, S.; Belhorma, B.; Bendahman, M.; et al. (Astrophysical Journal, 2022)
For several decades, the origin of ultra-high-energy cosmic rays (UHECRs) has been an unsolved question of high-energy astrophysics. One approach for solving this puzzle is to correlate UHECRs with high-energy neutrinos, since neutrinos are a direct probe of hadronic interactions of cosmic rays and are not deflected by magnetic fields. In this paper, we present three different approaches for correlating the arrival directions of neutrinos with the arrival directions of UHECRs. The neutrino data are provided by the IceCube Neutrino Observatory and ANTARES, while the UHECR data with energies above similar to 50 EeV are provided by the Pierre Auger Observatory and the Telescope Array. All experiments provide increased statistics and improved reconstructions with respect to our previous results reported in 2015. The first analysis uses a high-statistics neutrino sample optimized for point-source searches to search for excesses of neutrino clustering in the vicinity of UHECR directions. The second analysis searches for an excess of UHECRs in the direction of the highest-energy neutrinos. The third analysis searches for an excess of pairs of UHECRs and highest-energy neutrinos on different angular scales. None of the analyses have found a significant excess, and previously reported overfluctuations are reduced in significance. Based on these results, we further constrain the neutrino flux spatially correlated with UHECRs.
CRIS-Team WoS Importer:2022-08-26

Second Harmonic Generation from metallic and dielectric spherical nanoparticles - Peukert, Wolfgang; Wunderlich, Sarina; Zhuromskyy, Oleksandr; Schürer, Benedikt; Haderlein, Michael; Sauerbeck, Christian; Peschel, Ulf (2012 Conference on Lasers and Electro-Optics (CLEO), 2012)
Due to symmetry-breaking at an interface, Second Harmonic Generation (SHG) is an extremely surface sensitive process. Therefore it is a widely used tool to study surfaces. Applied to colloidal nanoparticles it offers efficient means to monitor growth and molecular adsorption processes in real time and in situ. This makes SHG a preferred method to study the formation of core-shell plasmonic nanoparticles, which recently became quite popular because of their strong and tunable plasmonic resonances.
Keywords: Symmetry; spherical; nanoparticle; second; harmonic; generation; plasmon; Optical; surface; wave; Harmonic analysis; Plasmons; Frequency conversion; Dielectrics

Second Harmonic Light Scattering from Spherical Polyelectrolyte Brushes - Peukert, Wolfgang; Schürer, Benedikt; Hoffmann, Martin; Wunderlich, Sarina; Peschel, Ulf; Harnau, Ludger; Ballauf, Matthias (Journal of Physical Chemistry C, 2011)
Optical second harmonic generation (SHG) was applied to study the shell layer of spherical polyelectrolyte brushes (SPB) as a function of ionic strength. The particles consist of a polystyrene core from which linear chains of a quenched polyelectrolyte are grafted. Compared to all systems studied by SHG previously, the shell layer in this study has a remarkable thickness of ca. 100 nm. Angle-resolved second harmonic (SH) scattering profiles were recorded and compared to simulations with different model geometries using a nonlinear Mie scattering model. The analysis reveals that the second harmonic signal is not generated by the polyelectrolyte molecules, but rather by oriented and polarized water molecules at the inner (polystyrene / polyelectrolyte) and at the outer (polyelectrolyte / solvent) interface of the polyelectrolyte shell. The results demonstrate that angle-resolved SH light scattering provides direct access to the structure of water and the screening of charges at the inner and outer interface of the polyelectrolyte shell. Correspondingly, this work sets the experimental and theoretical basis for the study of the extended interfacial layer of electrosterically stabilized particles by SH light scattering.
Keywords: optical; second; harmonic; generation; particle; polyelectrolyte

Seeded and unseeded high-order parametric down-conversion - Okoth, Cameron; Cavanna, Andrea; Joly, Nicolas; Chekhova, Maria (Physical Review A, 2019)
Spontaneous parametric down-conversion (SPDC) has been one of the foremost tools in quantum optics for over five decades. Over that time, it has been used to demonstrate some of the curious features that arise from quantum mechanics. Despite the success of SPDC, its higher-order analogs have never been observed, even though it has been suggested that they generate far more unique and exotic states than SPDC. An example of this is the emergence of non-Gaussian states without the need for postselection. Here we calculate the expected rate of emission for nth-order SPDC with and without external stimulation (seeding). Focusing primarily on third-order parametric down-conversion, we estimate the photon detection rates in a rutile crystal for both the unseeded and seeded regimes.
CRIS-Team WoS Importer:2019-04-18

Segmentation of Fat and Fascias in Canine Ultrasound Images - Rybakov, Oleksiy; Stromer, Daniel; Mischewski, Irina; Maier, Andreas (Bildverarbeitung für die Medizin 2018 (BVM 2018), 2018)
The connective tissue between fat and muscle termed fascia has been of interest to the recent clinical and biological research. However, in the canine and human medicine, the anatomic knowledge is still limited. To analyze the superficial fascia in canine medicine, a database with around 200 ultrasound images of one dog has been created. The superficial fascia contains fat compartments and is closely connected to the surrounding structures such as the skin's dermis and the epimysium of the muscles. This work proposes a semi-automatic and fully-automatic segmentation algorithm separating the different layers of ultrasound images of canines. Both algorithms were evaluated on a set of 24 expert-labeled images achieving high accuracy scores up to 95.9
Keywords: fascia; segmentation; ultrasound; canine; fat; open-source; GUI

Self-Catalyzed Growth of Vertically Aligned InN Nanorods by Metal-Organic Vapor Phase Epitaxy - Tessarek, C.; Fladischer, Stefanie; Dieker, Christel; Sarau, G.; Hoffmann, Björn; Bashouti, M.; Goebelt, M.; Heilmann, M.; Latzel, Michael; Butzen, E.; Figge, S.; Gust, A.; et al. (Nano Letters, 2016)
Vertically aligned hexagonal InN nanorods were grown mask-free by conventional metal organic vapor phase epitaxy without any foreign catalyst. The In droplets on top of the nanorod's indicate a self-catalytic vapor liquid solid growth mode. A systematic study on important growth parameters has been carried out for the optimization of nanorod morphology. The nanorod N-polarity, induced by high temperature nitridation of the sapphire substrate, IS necessary to achieve vertical growth. Hydrogen, usually inapplicable during InN growth due to formation of metallic indium, and silane are needed to enhance the aspect ratio and to reduce parasitic deposition beside the nanorods on the sapphire surface. The results reveal many similarities between InN and GaN nanorod growth showing that the process despite the large difference in growth temperature is similar. Transmission electron microscopy, spatially resolved energy-dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy have been performed to analyze the structural properties. Spatially resolved cathodoluminescence investigations are carried out to verify the optical activity of the InN nanorods. The InN nanorods are expected to be the material of choice for high-efficiency hot carrier solar cells.
Keywords: InN; nanorods; MOVPE; growth; vapor-liquid-solid; cathodoluminescence

Self-starting soliton modelocked femtosecond Chromium YAG laser using an antiresonant Fabry-Perot saturable absorber - Leuchs, Gerd; et al. (PDP oral presentation, 1996)
UnivIS-Import:2015-04-16:Pub.1996.nat.dphy.optik.1optik.selfst

Self-Starting Soliton-modelocked Femtosecond Cr(4+):YAG Laser Using an Antiresonant Fabry-Perot Saturable Absorber - Leuchs, Gerd; et al. (Applied Physics B-Lasers and Optics, 1997)
We set up a self-starting passively modelocked femtosecond Cr(4+):YAG laser using a low-finesse antiresonant Fabry-Pérot saturable absorber (A-FPSA). Stable transform-limited pulses were produced without the critical cavity alignment necessary for Kerr lens modelocking. We achieved 114-fs pulses with 94 mW output power at the telecommunication wavelength 1.5 μm. The pulse formation is demonstrated to be due to soliton modelocking. At higher intracavity energy multiple pulsing was observed and is explained by the saturation behaviour of the A-FPSA. In the multipulsing regime a pulse width as short as 95 fs and an averaged output power of up to 395 mW have been obtained. © Springer-Verlag 1997.
UnivIS-Import:2015-03-05:Pub.1997.nat.dphy.optik.1optik.selfst

Self-Switching Kerr Oscillations of Counterpropagating Light in Microresonators - Woodley, Michael T.M.; Hill, Lewis; Del Bino, Leonardo; Oppo, Gian Luca; Del'Haye, Pascal (Physical Review Letters, 2021)
We report the experimental and numerical observation of oscillatory antiphase switching between counterpropagating light beams in Kerr ring microresonators, where dominance between the intensities of the two beams is periodically or chaotically exchanged. Self-switching occurs in balanced regimes of operation and is well captured by a simple coupled dynamical system featuring only the self- and cross-phase Kerr nonlinearities. Switching phenomena are due to temporal instabilities of symmetry-broken states combined with attractor merging, which restores the broken symmetry on average. Self-switching of counterpropagating light is robust for realizing controllable, all-optical generation of waveforms, signal encoding, and chaotic cryptography.
CRIS-Team Scopus Importer:2021-02-12

Semiclassical limit of new path integral formulation from reduced phase space loop quantum gravity - Han, Muxin; Liu, Hsuan-Wei (Physical Review D - Particles, Fields, Gravitation and Cosmology, 2020)
Recently, a new path integral formulation of loop quantum gravity (LQG) has been derived in M. Han and H. Liu, Phys. Rev. D 101, 046003 (2020). from the reduced phase space formulation of the canonical LQG. This paper focuses on the semiclassical analysis of this path integral formulation. We show that dominant contributions of the path integral come from solutions of semiclassical equations of motion (EOMs), which reduce to Hamilton's equations of holonomies and fluxes h(e), p(a)(e) in the reduced phase space P-gamma of the cubic lattice gamma: dh(e)/d tau = h(e), H, dp(a)(e)/d tau = p(a)(e), H, where H is the discrete physical Hamiltonian. The semiclassical dynamics from the path integral becomes an initial value problem of Hamiltonian time evolution in P-gamma. Moreover when we take the continuum limit of the lattice gamma, these Hamilton's equations reproduce correctly classical reduced phase space EOMs of gravity coupled to dust fields in the continuum, as far as initial and final states are semiclassical. Our result proves that the new path integral formulation has the correct semiclassical limit and indicates that the reduced phase space quantization in LQG is semiclassically consistent. Based on these results, we compare this path integral formulation and the spin foam formulation, and show that this formulation has several advantages including the finiteness, the relation with canonical LQG, and the freedom from cosine and flatness problems.
CRIS-Team WoS Importer:2020-08-14

Sensing nanoparticles with a cantilever-based scannable optical cavity of low finesse and sub- λ3 volume - Kelkar, Hrishikesh; Wang, Daqing; Martin-Cano, Diego; Hoffmann, Björn; Christiansen, Silke; Götzinger, Stephan; Sandoghdar, Vahid (Physical Review Applied, 2015)
We report on the realization of an open plane-concave Fabry-Perot resonator with a mode volume below λ3 at optical frequencies. We discuss some of the less-common features of this microcavity regime and show that the ultrasmall mode volume allows us to detect cavity resonance shifts induced by single nanoparticles even at quality factors as low as 100. Being based on low-reflectivity micromirrors fabricated on a silicon cantilever, our experimental arrangement provides broadband operation, tunability of the cavity resonance, and lateral scanning. These features are interesting for a range of applications including biochemical sensing, modification of photophysics, and optomechanical studies.

Separated Schmidt modes in the angular spectrum of biphotons - Borshchevskaia, N. A.; Just, F.; Katamadze, K. G.; Cavanna, Andrea; Chekhova, Maria (Laser Physics Letters, 2019)
We prepared qudits based on angular multimode biphoton states by modulating the pump angular spectrum. The modes were prepared in the Schmidt basis and their intensity distributions did not overlap in space. This allows one to get rid of filtering losses while addressing single modes and to realize a single-shot qudit readout.
CRIS-Team WoS Importer:2019-07-26

Seven-octave high-brightness and carrier-envelope-phase-stable light source - Elu, Ugaitz; Maidment, Luke; Vamos, Lenard; Tani, Francesco; Novoa, David; Frosz, Michael H.; Badikov, Valeriy; Badikov, Dmitrii; Petrov, Valentin; Russell, Philip St. John; Biegert, Jens (Nature Photonics, 2020)
High-brightness sources of coherent and few-cycle-duration light waveforms with spectral coverage from the ultraviolet to the terahertz would offer unprecedented versatility and opportunities for a wide range of applications from bio-chemical sensing(1) to time-resolved and nonlinear spectroscopy, and to attosecond light-wave electronics(2,3). Combinations of various sources with frequency conversion(4,5) and supercontinuum generation(6-9) can provide relatively large spectral coverage, but many applications require a much broader spectral range(10) and low-jitter synchronization for time-domain measurements(11). Here, we present a carrier-envelope-phase (CEP)-stable light source, seeded by a mid-infrared frequency comb(12,13), with simultaneous spectral coverage across seven optical octaves, from the ultraviolet (340 nm) into the terahertz (40,000 nm). Combining soliton self-compression and dispersive wave generation in an anti-resonant-reflection photonic-crystal fibre with intra-pulse difference frequency generation in BaGa2GeSe6, the spectral brightness is two to five orders of magnitude above that of synchrotron sources. This will enable high-dynamic-range spectroscopies and provide numerous opportunities in attosecond physics and material sciences(14,15).
CRIS-Team WoS Importer:2021-01-01