@article{62862, abstract = {{Exciton polariton condensates are macroscopic coherent states in which topological excitations can be observed. In this work, we observe the excitation of the vortices and realize tuning the topological charge by manipulating the pumping configurations. Using a digital micromirror device, we constructed an annular pumping pattern where the inner and outer rings can be easily tuned. Both the number and the topological charge of the vortices can be changed by slightly tuning the inner ring position against the outer ring. The experimental results can be reproduced in theory by the Gross–Pitaevskii equation. Our work offers to generate and manipulate vortices in exciton polariton condensates using a straightforward optical method.}}, author = {{Ai, Qiang and Ma, Xuekai and Barkhausen, Franziska and Zhai, Xiaokun and Xing, Chunzi and Yang, Xinmiao and Wang, Peilin and Liu, Tianyu and Zhang, Yong and Gu, Yazhou and Li, Peigang and Li, Zhitong and Hatzopoulos, Zacharias and Savvidis, Pavlos G. and Schumacher, Stefan and Gao, Tingge}}, issn = {{0003-6951}}, journal = {{Applied Physics Letters}}, number = {{12}}, publisher = {{AIP Publishing}}, title = {{{Tuning polariton vortices in an asymmetric ring potential}}}, doi = {{10.1063/5.0287076}}, volume = {{127}}, year = {{2025}}, } @article{62865, author = {{Sun, Jinming and Chen, Manna and Schumacher, Stefan and Hu, Wei and Ma, Xuekai}}, issn = {{2469-9950}}, journal = {{Physical Review B}}, number = {{11}}, publisher = {{American Physical Society (APS)}}, title = {{{Higher-order dark solitons and control dynamics in microcavity polariton condensates}}}, doi = {{10.1103/p357-vyq8}}, volume = {{112}}, year = {{2025}}, } @article{62860, abstract = {{ The Quantum Internet, a network of quantum-enabled infrastructure, represents the next frontier in telecommunications, promising capabilities that cannot be attained by classical counterparts. A crucial step in realizing such large-scale quantum networks is the integration of entanglement distribution within existing telecommunication infrastructure. Here, we demonstrate a real-world scalable quantum networking testbed deployed within Deutsche Telekom’s metropolitan fibers in Berlin. Using commercially available quantum devices and standard add-drop multiplexing hardware, we distributed polarization-entangled photon pairs over dynamically selectable looped fiber paths ranging from 10 m to 60 km and showed entanglement distribution over up to approximately 100 km. Quantum signals, transmitted at 1324 nm (O-band), coexist with conventional bidirectional C-band traffic without dedicated fibers or infrastructure changes. Active stabilization of the polarization enables robust long-term performance, achieving entanglement Bell-state fidelity bounds between 85% and 99% and Clauser–Horne–Shimony–Holt parameter S -values between 2.36 and 2.74 during continuous multiday operation. By achieving a high-fidelity entanglement distribution with less than 1.5% downtime, we confirm the feasibility of hybrid quantum-classical networks under real-world conditions at the metropolitan scale. These results establish deployment benchmarks and provide a practical roadmap for telecom operators to integrate quantum capabilities. }}, author = {{Sena, Matheus and Flament, Mael and Andrewski, Shane and Caltzidis, Ioannis and Bigagli, Niccolò and Rieser, Thomas and Bello Portmann, Gabriel and Sekelsky, Rourke and Braun, Ralf-Peter and Craddock, Alexander N. and Schulz, Maximilian and Jöns, Klaus and Ritter, Michaela and Geitz, Marc and Holschke, Oliver and Namazi, Mehdi}}, issn = {{1943-0620}}, journal = {{Journal of Optical Communications and Networking}}, number = {{12}}, publisher = {{Optica Publishing Group}}, title = {{{High-fidelity quantum entanglement distribution in metropolitan fiber networks with co-propagating classical traffic}}}, doi = {{10.1364/jocn.575396}}, volume = {{17}}, year = {{2025}}, } @article{62912, abstract = {{We investigate the dynamics of wave packets in a parabolic optical lattice formed by combining an optical lattice with a global parabolic trap. Our study examines the phase space representation of the system's eigenstates by comparing them to the classical phase space of a pendulum, to which the system effectively maps. The analysis reveals that quantum states can exhibit mixed dynamics by straddling the separatrix. A key finding is that the dynamics around the separatrix enables the controlled creation of highly nonclassical states, distinguishing them from the classical oscillatory or rotational dynamics of the pendulum. By considering a finite momentum of the initial wave packet, we demonstrate various dynamical regimes. Furthermore, a slight energy mismatch between nearly degenerate states localized at opposite turning points of the trap potential results in controlled long-range dynamical tunneling. These results can be interpreted as quantum beating between a clockwise rotating and a counterclockwise rotating pendulum.}}, author = {{Ali, Usman and Holthaus, Martin and Meier, Torsten}}, issn = {{2643-1564}}, journal = {{Physical Review Research}}, number = {{1}}, publisher = {{American Physical Society (APS)}}, title = {{{Wave packet dynamics in parabolic optical lattices: From Bloch oscillations to long-range dynamical tunneling}}}, doi = {{10.1103/physrevresearch.7.013141}}, volume = {{7}}, year = {{2025}}, } @article{62911, abstract = {{In this paper, we theoretically study the spectral and temporal properties of pulsed spontaneous parametric down-conversion (SPDC) generated in lossy waveguides. Our theoretical approach is based on the formalism of Gaussian states and the Langevin equation, which is elaborated for weak parametric down-conversion and photon-number-unresolved click detection. Using the example of frequency-degenerate type-II SPDC generated under the pump-idler group-velocity-matching condition, we show how the joint-spectral intensity, mode structure, normalized second-order correlation function, and Hong-Ou-Mandel interference pattern depend on internal losses of the SPDC process. We found that the joint-spectral intensity is almost insensitive to internal losses, while the second-order correlation function shows a strong dependence on them, being different for the signal and idler beams in the presence of internal losses. Based on the sensitivity of the normalized second-order correlation function, we show how its measurement can be used to experimentally determine internal losses.}}, author = {{Kopylov, Denis A. and Stefszky, Michael and Meier, Torsten and Silberhorn, Christine and Sharapova, Polina R.}}, issn = {{2643-1564}}, journal = {{Physical Review Research}}, number = {{3}}, publisher = {{American Physical Society (APS)}}, title = {{{Spectral and temporal properties of type-II parametric down-conversion: The impact of losses during state generation}}}, doi = {{10.1103/zp72-7qwl}}, volume = {{7}}, year = {{2025}}, } @inproceedings{62913, author = {{Hunstig, Anna and Peitz, Sebastian and Rose, Hendrik and Meier, Torsten}}, booktitle = {{2024 IEEE 63rd Conference on Decision and Control (CDC)}}, publisher = {{IEEE}}, title = {{{Accelerating the analysis of optical quantum systems using the Koopman operator}}}, doi = {{10.1109/cdc56724.2024.10886589}}, year = {{2025}}, } @inproceedings{62920, author = {{Fox, Marvin Lee and Peeters, Hendrik and Fechner, Sabine}}, booktitle = {{GDCP Jahrestagung}}, keywords = {{Artificial intelligence, education, chemistry}}, location = {{Frankfurt}}, title = {{{KI-Einsatz durch Lernende im Erkenntnisgewinnungsprozess - ein Review}}}, year = {{2025}}, } @article{60568, author = {{Bocchini, Adriana and Kollmann, S. and Gerstmann, Uwe and Schmidt, Wolf Gero and Grundmeier, Guido}}, issn = {{0039-6028}}, journal = {{Surface Science}}, publisher = {{Elsevier BV}}, title = {{{Phosphonic acid adsorption on α-Bi2O3 surfaces}}}, doi = {{10.1016/j.susc.2025.122776}}, volume = {{760}}, year = {{2025}}, } @article{61353, abstract = {{Abstract Muonic hydrogen is an exotic atom where a muon instead of an electron is bound to a proton. The comparably high mass of the muon (≈ 207 · me ) has two important effects, (i) the reduced mass of the system becomes more important, and (ii) the muon is localized much closer to the nucleus. Thus, muonic hydrogen is not only excellently suitable for evaluating highly precise quantum electrodynamic (QED) calculations, but may also be used for assessing new approaches including finite nuclear size (FNS) effects to evaluate the proton structure and improve calculation schemes for the hyperfine splittings of many-particle systems, as e.g. to be implemented in density functional theory (DFT) software packages. Here, starting from Dirac’s equation we calculate the relativistic hyperfine splitting of the ground state and several excited states of muonic hydrogen analytically for different charge and magnetization models. The FNS related hyperfine shifts are compared with the differences between QED calculations and experimental measurements. This comparison also allows to unravel the role of the reduced mass, which is on one hand crucial in case of muonic atoms, but on the other hand is by no means well defined in relativistic quantum mechanics.}}, author = {{Franzke, Katharina L. and Schmidt, Wolf Gero and Gerstmann, Uwe}}, issn = {{1742-6588}}, journal = {{Journal of Physics: Conference Series}}, number = {{1}}, publisher = {{IOP Publishing}}, title = {{{Finite-size and relativistic effects onto hyperfine interaction of muonic hydrogen}}}, doi = {{10.1088/1742-6596/3027/1/012001}}, volume = {{3027}}, year = {{2025}}, } @inproceedings{61352, author = {{Devaraj, Vasanthan and Ruiz Alvarado, Isaac Azahel and Lee, Jongmin and Oh, Jin-Woo and Gerstmann, Uwe and Schmidt, Wolf Gero and Zentgraf, Thomas}}, booktitle = {{2025 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)}}, publisher = {{IEEE}}, title = {{{Dynamic and Reversible Plasmonic Nanogaps From Isolated Dimer Nanoparticles via Self-Assembly}}}, doi = {{10.1109/cleo/europe-eqec65582.2025.11109762}}, year = {{2025}}, } @article{62866, abstract = {{Abstract The development of efficient and broadly applicable n‐doping strategies for organic semiconductors (OSCs) is crucial for advancing the performance of various organic electronic devices. Here, a novel nucleophilic‐attack n‐doping mechanism is unveiled that achieves exceptionally high conductivity in doped OSC films and demonstrates broad applicability across OSCs. The remarkable efficacy of n‐Butyl lithium (n‐BuLi) is highlighted in n‐doping C 60 and PC 61 BM, achieving a conductivity of 1.27 S cm −1 and 2.57 S cm −1 , respectively, which are among the highest reported values for these materials. The investigation reveals that the n‐BuLi anion interacts with electron‐deficient units in OSCs, generating a carbanion that facilitates efficient electron transfer for n‐doping. This mechanism is further validated across diverse fullerenes, polymeric, and small molecule OSCs, and is extendable to other high‐performance dopants such as tert‐Butyllithium (tert‐BuLi) and sodium ethoxide (NaOEt). Device studies show that n‐BuLi‐doped C 60 enables substantially improved diode rectification, attributed to greater junction built‐in potential. These findings establish a unified chemical‐bonding‐based n‐doping paradigm, complementing existing electrophilic‐attack p‐doping concepts, and pave the way for achieving efficient doping of OSCs for advanced organic electronic applications. }}, author = {{Wei, Huan and Wu, Tong and Dong, Chuanding and Chen, Chen and Gong, Zhenqi and Xia, Jiangnan and Peng, Chengyuan and Ding, Jiaqi and Zhang, Yu and Shi, Wenpei and Schumacher, Stefan and Zhang, Xue and Bai, Yugang and Jiang, Lang and Liao, Lei and Nguyen, Thuc‐Quyen and Hu, Yuanyuan}}, issn = {{2198-3844}}, journal = {{Advanced Science}}, publisher = {{Wiley}}, title = {{{Efficient n‐Doping of Organic Semiconductors via a Broadly Applicable Nucleophilic‐Attack Mechanism}}}, doi = {{10.1002/advs.202520487}}, year = {{2025}}, } @article{60992, abstract = {{Non-Hermitian systems hosting exceptional points (EPs) exhibit enhanced sensitivity and unconventional mode dynamics. Going beyond isolated EPs, here we report on the existence of exceptional rings (ERs) in planar optical resonators with specific form of circular dichroism and TE-TM splitting. Such exceptional rings possess intriguing topologies as discussed earlier for condensed matter systems, but they remain virtually unexplored in presence of nonlinearity, for which our photonic platform is ideal. We find that when Kerr-type nonlinearity (or saturable gain) is introduced, the linear ER splits into two concentric ERs, with the larger-radius ring being a ring of third-order EPs. Transitioning from linear to nonlinear regime, we present a rigorous analysis of spectral topology and report enhanced and adjustable perturbation response in the nonlinear regime. Whereas certain features are specific to our system, the results on non-Hermitian spectral topology and nonlinearity-enhanced perturbation response are generic and equally relevant to a broad class of other nonlinear non-Hermitian systems, providing a universal framework for engineering ERs and EPs in nonlinear non-Hermitian systems.}}, author = {{Wingenbach, Jan and Ares Santos, Laura and Ma, Xuekai and Sperling, Jan and Schumacher, Stefan}}, journal = {{Arxiv}}, publisher = {{Arxiv}}, title = {{{Sensitivity and Topology of Exceptional Rings in Nonlinear Non-Hermitian Planar Optical Microcavities}}}, doi = {{10.48550/ARXIV.2507.07099}}, year = {{2025}}, } @article{62926, abstract = {{Abstract Negatively charged boron vacancies () in hexagonal boron nitride (hBN) are emerging as promising solid‐state spin qubits due to their optical accessibility, structural simplicity, and compatibility with photonic platforms. However, quantifying the density of such defects in thin hBN flakes has remained elusive, limiting progress in device integration and reproducibility. Here, an all‐optical method is presented to quantify defect density in hBN by correlating Raman and photoluminescence (PL) signatures with irradiation fluence. Two defect‐induced Raman modes, D1 and D2, are identified and assigned them to vibrational modes of using polarization‐resolved Raman measurements and density functional theory (DFT) calculations. By adapting a numerical model originally developed for graphene, an empirical relationship linking Raman (D1, E 2g ) and PL intensities is established to absolute defect densities. This method is universally applicable across various irradiation types and uniquely suited for thin flakes, where conventional techniques fail. The approach enables accurate, direct, and non‐destructive quantification of spin defect densities down to 10 15  defects/cm 3 , offering a powerful tool for optimizing and benchmarking hBN for quantum optical applications. }}, author = {{Patra, Atanu and Konrad, Paul and Sperlich, Andreas and Biktagirov, Timur and Schmidt, Wolf Gero and Spencer, Lesley and Aharonovich, Igor and Höfling, Sven and Dyakonov, Vladimir}}, issn = {{1616-301X}}, journal = {{Advanced Functional Materials}}, publisher = {{Wiley}}, title = {{{Quantifying Spin Defect Density in hBN via Raman and Photoluminescence Analysis}}}, doi = {{10.1002/adfm.202517851}}, year = {{2025}}, } @article{62980, abstract = {{We introduce a new classification of multimode states with a fixed number of photons. This classification is based on the factorizability of homogeneous multivariate polynomials and is invariant under unitary transformations. The classes physically correspond to field excitations in terms of single and multiple photons, each of which is in an arbitrary irreducible superposition of quantized modes. We further show how the transitions between classes are rendered possible by photon addition, photon subtraction, and photon-projection nonlinearities. We explicitly put forward a design for a multilayer interferometer in which the states for different classes can be generated with state-of-the-art experimental techniques. Limitations of the proposed designs are analyzed using the introduced classification, providing a benchmark for the robustness of certain states and classes.}}, author = {{Kopylov, Denis A. and Offen, Christian and Ares, Laura and Wembe Moafo, Boris Edgar and Ober-Blöbaum, Sina and Meier, Torsten and Sharapova, Polina R. and Sperling, Jan}}, issn = {{2643-1564}}, journal = {{Physical Review Research}}, number = {{3}}, publisher = {{American Physical Society (APS)}}, title = {{{Multiphoton, multimode state classification for nonlinear optical circuits}}}, doi = {{10.1103/sv6z-v1gk}}, volume = {{7}}, year = {{2025}}, } @article{63021, abstract = {{Bell measurements, entailing the projection onto one of the Bell states, play a key role in quantum information and communication, where the outcome of a variety of protocols crucially depends on the success probability of such measurements. Although in the case of qubit systems, Bell measurements can be implemented using only linear optical components, the same result is no longer true for qudits, where at least the use of ancillary photons is required. In order to circumvent this limitation, one possibility is to introduce nonlinear effects. In this work, we adopt the latter approach and propose a scalable Bell measurement scheme for high-dimensional states, exploiting multiple squeezer devices applied to a linear optical circuit for discriminating the different Bell states. Our approach does not require ancillary photons, is not limited by the dimension of the quantum states, and is experimentally scalable, thus paving the way toward the realization of an effective high-dimensional Bell measurement.}}, author = {{Bianchi, Luca and Marconi, Carlo and Sperling, Jan and Bacco, Davide}}, issn = {{2643-1564}}, journal = {{Physical Review Research}}, number = {{2}}, publisher = {{American Physical Society (APS)}}, title = {{{Predetection squeezing as a resource for high-dimensional Bell-state measurements}}}, doi = {{10.1103/physrevresearch.7.023038}}, volume = {{7}}, year = {{2025}}, } @article{62859, abstract = {{Frequency-filtered photon correlations have been proven to be extremely useful in grasping how the detection process alters photon statistics. Harnessing the spectral correlations also permits refinement of the emission and unraveling of previously hidden strong correlations in a plethora of quantum-optical systems under continuous-wave excitation. In this work, we investigate such correlations for time-dependent excitation and develop a methodology to compute efficiently time-integrated correlations, which are at the heart of the photon-counting theory, and subsequently apply it to analyze the photon emission of pulsed systems. By combining this formalism with the —which facilitates frequency-resolved correlations—we demonstrate how spectral filtering enhances single-photon purity and suppresses multiphoton noise in time-bin-encoded quantum states. Specifically, filtering the central spectral peak of a dynamically driven two-level system boosts temporal coherence and improves the fidelity of time-bin entanglement preparation, even under conditions favoring multiphoton emission. These results establish spectral filtering as a critical tool for tailoring photon statistics in pulsed quantum light sources.}}, author = {{Bermúdez-Feijóo, Santiago and Zubizarreta Casalengua, Eduardo and Müller, Kai and Jöns, Klaus}}, issn = {{2643-1564}}, journal = {{Physical Review Research}}, number = {{3}}, publisher = {{American Physical Society (APS)}}, title = {{{Spectral correlations of dynamical resonance fluorescence}}}, doi = {{10.1103/jmy9-bd3l}}, volume = {{7}}, year = {{2025}}, } @misc{63050, author = {{Güsken, Nicholas Alexander}}, title = {{{Beam steering device and electronic apparatus including the same}}}, year = {{2025}}, } @article{62269, abstract = {{The titanium in-diffused lithium niobate waveguide platform is well-established for reliable prototyping and packaging of many quantum photonic components at room temperature. Nevertheless, compatibility with certain quantum light sources and superconducting detectors requires operation under cryogenic conditions. We characterize alterations in phase-matching and mode guiding of a non-degenerate spontaneous parametric down-conversion process emitting around 1556 nm and 950 nm, under cryogenic conditions. Despite the effects of pyroelectricity and photorefraction, the spectral properties match our theoretical model. Nevertheless, these effects cause small but significant variations within and between cooling cycles. These measurements provide a first benchmark against which other nonlinear photonic integration platforms, such as thin-film lithium niobate, can be compared.}}, author = {{Lange, Nina Amelie and Lengeling, Sebastian and Mues, Philipp and Quiring, Viktor and Ridder, Werner and Eigner, Christof and Herrmann, Harald and Silberhorn, Christine and Bartley, Tim}}, issn = {{1094-4087}}, journal = {{Optics Express}}, number = {{24}}, publisher = {{Optica Publishing Group}}, title = {{{Widely non-degenerate nonlinear frequency conversion in cryogenic titanium in-diffused lithium niobate waveguides}}}, doi = {{10.1364/oe.578108}}, volume = {{33}}, year = {{2025}}, } @article{63072, abstract = {{Titanium alloys are widely employed for biomedical implants due to their high strength, biocompatibility, and corrosion resistance, yet their lack of intrinsic antibacterial activity remains a major limitation. Incorporating copper, an antibacterial and β-stabilising element, offers a promising strategy to enhance implant performance. This study investigates Ti-6Al-7Nb modified with 1–9 wt.% Cu via in situ alloying during metal-based laser powder bed fusion (PBF-LB/M), with the aim of assessing processability, microstructural evolution, and mechanical properties. Highly dense samples (>99.9%) were produced across all Cu levels, though chemical homogeneity strongly depended on processing parameters. Increasing Cu content promoted β-phase stabilisation, Ti2Cu precipitation, and pronounced grain refinement. Hardness and yield strength increased nearly linearly with Cu addition, while ductility decreased sharply at ≥5 wt.% Cu due to intermetallic formation, hot cracking, and brittle fracture. These results illustrate both the opportunities and constraints of rapid alloy screening via PBF-LB/M. Overall, moderate Cu additions of 1–3 wt.% provide the most favourable balance between mechanical performance, manufacturability, and potential antibacterial functionality. These findings provide a clear guideline for the design of Cu-functionalised titanium implants and demonstrate the efficiency of in situ alloy screening for accelerated materials development.}}, author = {{Steinmeier, Paul and Hoyer, Kay-Peter and Lopes Dias, Nelson Filipe and Zielke, Reiner and Tillmann, Wolfgang and Schaper, Mirko}}, issn = {{2073-4352}}, journal = {{Crystals}}, keywords = {{Biomaterial, In Situ Alloying, Titanium, Additive Manufacturing}}, number = {{12}}, publisher = {{MDPI AG}}, title = {{{In Situ Alloying of Ti-6Al-7Nb with Copper Using Laser Powder Bed Fusion}}}, doi = {{10.3390/cryst15121053}}, volume = {{15}}, year = {{2025}}, } @inproceedings{62921, author = {{Fox, Marvin Lee and Peeters, Hendrik and Fechner, Sabine}}, booktitle = {{Conference of The European Science Education Research Association (ESERA)}}, keywords = {{Artificial intelligence, education, chemistry}}, location = {{Copenhagen, Denmark}}, title = {{{How can students be supported by ChatGPT as a tutor in hands-on chemistry education?}}}, year = {{2025}}, }