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Physics Physics Optics

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Friday 4 September

Optics

Band Gaps and Localization of Surface Waves at Hyperbolic Material and Topological Insulator Interfaces

Andrei I. Maimistov, Ildar R. Gabitov and Ilia Kuk

We develop analytical criteria for surface electromagnetic waves at interfaces between hyperbolic materials and topological insulators. The analysis identifies propagation conditions, field penetration depths, and spectral band gaps. In the lossless model, the band edge is governed primarily by dielectric contrast, while the bulk topological coupling produces only a small shift and a weak correction to the dispersion. For structures combining hexagonal boron nitride with bismuth selenide, a thin topological insulator film on a dielectric substrate with low permittivity can substantially broaden the accessible propagation window. We also analyze a dissipative titanium and silicon hyperbolic effective medium interfaced with bismuth selenide. To make the complex branch structure visible, this lossy calculation uses an intentionally enhanced interface response and is therefore illustrative rather than a quantitative prediction for a conventional topological insulator. In the lossy case, a root of the dispersion relation represents a physical guided mode only when the fields decay away from the interface, attenuate consistently along the propagation direction, have finite penetration depths, and exhibit a consistent energy flow profile. Apparent gaps and jumps can occur when the complex quantities controlling transverse decay approach square root branch cuts. These results provide design guidelines for controlling dispersion, confinement, band gaps, and propagation loss in mid-infrared photonic structures.
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Thursday 3 September

Optics

Nonlinear Photoemission for Bright Beams in X-Band Photoinjectors

Casey Timms, Lucas Malin, Kevin Eckrosh et al. (+15 more)

The ongoing development of low-cost and compact x-ray light sources is vital for increasing the number of experiments that can be performed at the atomic scale. One option for a compact and simple photoinjector is to operate in blow-out mode, in which a high-charge, short-bunch length electron beam self-expands by space-charge forces into a uniformly ellipsoidal shape. This mode necessitates a photoinjector whose initial electron pulse has a pulse duration on the order of $100$ fs. A photoinjector utilizing linear photoemission with an ultraviolet laser in this regime presents significant technical challenges, as many optical substrates degrade at these wavelengths. In this paper, we present an alternative design that uses nonlinear photoemission to produce electron beams with high charge and short bunch length in an X-band (9300 MHz) photoinjector. This photoinjector design produces an electron beam with a bunch charge of up to $200$ pC, an RMS bunch length of $291$ fs, a normalized transverse emittance of $1$ to $1.4$ mm$\cdot$mrad, and an energy spread of $10^{-4}$. This results in a beam brightness of $10^{18}$ A/m$^2$, which is bright enough for our beamline's purposes. We also present ongoing efforts are aimed at further increasing the electron beam brightness by using a spatial light modulator to shape the laser profile at the cathode.
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All authors Casey Timms, Lucas Malin, Kevin Eckrosh, Sean E. Tilton, Lidia C. Santander, Hyung Seo Lee, Rejul Jaswal, Alex Gardeck, Eric Everett, Alan Dupre, Mukhtar Hussain, Sami Tantawi, William Graves, Henrik Loos, Mark Holl, Arvinder Sandhu, Robert Kaindl, Samuel Teitelbaum

Optics · Cross-listed from cs.AI

When Quantization Breaks Memory: Recurrent-State Write-Back in Low-Precision Temporal Inference

Ismail Erbas, Xavier Intes and Vikas Pandey

Quantization is widely used to reduce the computational and memory demands of neural-network inference. In recurrent networks, however, the quantized state is stored and returned at the next time step, so the rule used to store that state can alter subsequent computations. Here, we introduce recurrent-state write-back to denote this rule and isolate its effect in a compact GRU encoder–decoder for fluorescence lifetime imaging, a molecular imaging modality used in quantitative biological imaging. A central task is estimating two lifetime parameters, the short-lived component {\tau}1 and the long-lived component {\tau}2, from high-noise time-resolved fluorescence signals. Holding the trained model fixed, replacing continuous state propagation with deterministic 4-bit state storage increases estimation errors for {\tau}1 and {\tau}2 by approximately 70x and 300x, respectively. Failure occurs when repeated small updates remain below the write threshold, leaving the stored state nearly fixed while the network continues to propose change. Error feedback, residual memory, and direction memory carry information from these suppressed updates across time and recover accuracy without retraining. Precision sweeps show that increasing state precision can worsen a fixed recurrent solution, while matched training shows that compatibility with the state interface can be learned. To test whether this behavior extends beyond the GRU, we repeat the post-training intervention in an independently trained LSTM, where coarse write-back reproduces the failure, error feedback restores accuracy, and state-specific interventions reveal greater sensitivity of the cell state than the hidden state. Our results establish recurrent-state write-back as a key determinant of low-precision recurrent dynamics and identify the state-storage interface as a central design consideration for quantized recurrent inference.
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Optics · Cross-listed from quant-ph

Proof-of-principle long-distance Sagnac twin-field quantum key distribution network

Reem Mandil, Yen-An Shih, Abhay Verma et al. (+2 more)

Twin-field (TF) quantum key distribution (QKD) offers a promising approach to long-distance QKD networks due to its superior performance over large channel losses. Due to specialized hardware requirements, nearly all long-distance TFQKD demonstrations have only two users exchanging keys, rather than a network with three or more users. In this work, we experimentally demonstrate a proof-of-principle three-user-pair Sagnac TFQKD network spanning 127-km using single-photon avalanche detectors without any active phase stabilization or postcompensation. We implement efficient procedures for maintaining polarization stability and circumventing Rayleigh backscattering noise to achieve a stable Sagnac interference visibility of $93\pm1$% over one hour. A secure key rate of $1.398\times10^{-5}$ bits per pulse is achieved over an asymmetric communication channel with 102-km fiber and 45-dB overall loss. To our knowledge, this is the first TFQKD network without active phase stabilization or postcompensation achieved over long fibers. Our results represent a highly practical and cost-effective approach to long-distance QKD networks.
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All authors Reem Mandil, Yen-An Shih, Abhay Verma, Li Qian, Hoi-Kwong Lo

Optics

Ultrafast Control of Lifetime in High Q Anisotropic Plasmon Polaritons

Romain Tirole, Giacomo Venturi, Emroz Khan et al. (+6 more)

Losses are a major roadblock in the technological implementation of surface plasmons at optical frequencies. The recent emergence of MoOCl2, a correlated van-der-Waals material with strongly anisotropic optical properties, offers new avenues to circumvent this limit. We report the far-field observation of high-Q surface plasmon polaritons in this material, arising from the anisotropic hybridisation of surface plasmons and dielectric modes. We then explore nonlinear pumping of intraband electrons to the conduction band in these structures, leading, contrary to intuition, to an abrupt increase in the lifetime of the polariton resonance, despite the injection of hot electrons. This counterintuitive phenomenon stems from the competition between photon and plasmon excitations in a lenticular polariton resonance, yielding a largely tuneable lifetime at ultrafast speeds.
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All authors Romain Tirole, Giacomo Venturi, Emroz Khan, Lin Jing, Lin Nan, Nicola Melchioni, Andrea Mancini, Antonio Ambrosio, Andrea Alù

Optics

Twin-photon generation in a silicon nitride microresonator

Franz Pacher, Haochen Yan, Alekhya Ghosh et al. (+8 more)

Photonic chips with silicon nitride ($\mathrm{Si_3N_4}$) microring resonators are well established as heralded single-photon sources, but their operation as frequency-degenerate twin-photon sources has not previously been demonstrated. Here, we realise a twin-photon source at telecommunication wavelengths in a $\mathrm{Si_3N_4}$ ring microresonator via an inverse four-wave mixing (FWM) process, in which two photons from spectrally distinct pumps are converted into a pair of identical twin photons. The measurements show a maximum coincidence-to-accidental ratio (CAR) of $5.4\pm0.6$. In addition, the microresonator functions as a heralded single-photon source through pump-degenerate spontaneous four-wave mixing (SFWM), exhibiting a spectral purity of $P=0.67\pm0.05$ and a heralded anti-bunching of $g^{(2)}_h(0)=0.0042\pm0.0015$. Together, these results demonstrate both photon-generation schemes on a single integrated $\mathrm{Si_3N_4}$ platform, highlighting its potential for scalable, tailored quantum light generation.
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All authors Franz Pacher, Haochen Yan, Alekhya Ghosh, Arghadeep Pal, Toby Bi, Hao Zhang, Lixing You, Hao Li, Daniela Salvoni, Shuangyou Zhang, Pascal Del'Haye

Optics · Cross-listed from quant-ph

Quantum-Enhanced Phase Estimation with Photon-Added Even and Odd Coherent States in an SU(1,1) Interferometer

Abdelmajid El Maaroufi, Mouad Ait Maskour, Bouchra Maroufi et al. (+2 more)

We investigate phase estimation in an SU(1,1) interferometer employing $m$-photon-added even and odd coherent states as nonclassical input resources. The phase sensitivity is evaluated through intensity detection and the error propagation method, while the ultimate precision limit is determined from the quantum Cramér-Rao bound with the quantum Fisher information serving as the relevant metrological quantity. Our results demonstrate that photon addition significantly enhances the phase sensitivity, increases the quantum Fisher information, and reduces the quantum Cramér-Rao bound, leading to a clear improvement over the corresponding even and odd coherent states. Furthermore, the achievable sensitivity exceeds the standard quantum limit and gradually approaches the Heisenberg scaling with increasing photon-addition number. We also find that the $m$-photon-added even coherent states exhibit a modest advantage over their odd counterparts. As $m$ increases, however, this distinction becomes progressively weaker, suggesting that photon addition diminishes the role of the initial parity of the coherent state in determining the interferometric performance.
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All authors Abdelmajid El Maaroufi, Mouad Ait Maskour, Bouchra Maroufi, Mohammed Daoud, Saeed Haddadi

Optics

Cavity Ring-Down Spectroscopy at Benchmark-Level Sub-Permille Accuracy Enabled by a System-Level Detection Transfer Function

Rajesh Chell, Marcin Gibas, Szymon Wójtewicz et al. (+3 more)

Cavity ring-down spectroscopy (CRDS) is widely used for sensitive optical absorption measurements, but its quantitative accuracy can be limited at the few-percent level by systematic distortions originating in the CRDS detection system, particularly at short ring-down times. These limitations can restrict demanding spectroscopic applications requiring sub-permille accuracy, including atmospheric sensing, tests of ab initio theory and fundamental physics, and quantum-based optical gas standards. Here we develop a methodology based on a system-level detection transfer function describing the complete CRDS detection-system response, including detector, electronics, and digitization stages, and use it to correct previously unaccounted-for instrumental distortions in retrieved absorption. We demonstrate the method on a CO absorption line measured down to very short ring-down times using multiple independent CRDS detection configurations, initially exhibiting line-area biases of up to 14%. After applying the transfer-function correction, all systems converge to a common value, with the bias relative to the most accurate ab initio-validated reference data reaching the sub-permille level and the accuracy improving by a factor of 41–87. The proposed framework brings well-established CRDS to the level of the most accurate reference methods without requiring specialized measurement schemes or external calibration standards, making benchmark-quality measurements more widely accessible.
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All authors Rajesh Chell, Marcin Gibas, Szymon Wójtewicz, Jakub Łasocha, Daniel Lisak, Agata Cygan

Optics · Cross-listed from cond-mat.quant-gas

Three-observable measurement of the critical velocity in a paraxial superfluid of light flowing past a mobile impurity

T. Aladjidi, M. Baker-Rasooli, T. D. Ferreira et al. (+4 more)

We report the measurement of the critical velocity of a paraxial superfluid of light flowing past a mobile impurity, realized using a dual-wavelength optical scheme in a warm vapor of $^{87}\text{Rb}$. The superflow is two-dimensional by nature, while the impurity features a highly repulsive potential, a large tunable radius, and a finite mass. The critical velocity is evaluated by simultaneously monitoring three complementary observables: the number of vortices nucleated in the wake of the impurity, the hydrodynamic force exerted on it, and its displacement velocity relative to the flow. These independent methods yield consistent values for the critical velocity, which remain systematically below the Landau criterion and decrease with the impurity radius, in qualitative agreement with theoretical expectations. Our results demonstrate the reliability of these combined diagnostics, establishing paraxial superfluids of light as a versatile platform for exploring the impurity problem in quantum hydrodynamics.
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All authors T. Aladjidi, M. Baker-Rasooli, T. D. Ferreira, A. Bramati, M. Albert, Q. Glorieux, P.-É. Larré

Optics

Thermal Noise in Optical Coatings: A Rigorous Opto-Mechanical Comparison of Nanolaminates and Isotropic Mixtures

Vincenzo Pierro, Vincenzo Fiumara, Veronica Granata et al. (+1 more)

We investigate whether a perfectly ordered periodic nanolaminate is intrinsically less mechanically dissipative than an isotropic co-sputtered mixture designed to provide the exact same optical function. Focusing on a room-temperature SiO2/TiO2 system, we compare coating Brownian dissipation under strict parity of optical thickness and effective refractive index. Amorphous phases are modeled using complex Young's moduli and real Poisson's ratios. The comparison is highly non-trivial: while the nanolaminate is optically optimal, its structural anisotropy forces in-plane shear to operate at the highly dissipative Voigt upper bound, mechanically penalizing it against an isotropic medium. The nanolaminate is treated via exact optical (Wiener) and mechanical (Backus) relations. The isotropic mixture is described by optical closures (Lorentz–Lorenz, Bruggeman) coupled to a complex mechanical self-consistent scheme. To assess uncertainty from the unknown co-sputtered morphology, we explore rigorous optical and mechanical admissible regions in the complex plane. Owing to the small intrinsic losses of SiO2/TiO2, these regions collapse into extremely narrow lenses, strictly limiting microstructural uncertainty. Across all realistic isotropic closures, the nanolaminate systematically exhibits lower mechanical dissipation than the co-sputtered mixture. Even against the thermodynamic lower bound of the isotropic state, this topological advantage remains valid for high effective refractive indices. We prove the ordered architecture exploits the optical upper bound to minimize the required volume fraction of the highly dissipative high-index phase, overwhelmingly overcompensating for its intrinsic mechanical anisotropy penalty.
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All authors Vincenzo Pierro, Vincenzo Fiumara, Veronica Granata, Guerino Avallone

Optics

3D scattered light imaging: extracting 3D fiber orientations from 1D line profiles in brain imaging

Dennis Scheidt, Charlotte Voß, Cristian Rosero Arias et al. (+6 more)

Understanding the 3D fiber architecture of the brain at the microscopic scale is essential for revealing its structural connectivity and function. Polarization-based optical imaging (3D-PLI) techniques enable high-fidelity reconstruction of single nerve fiber orientations but struggle to resolve fiber crossings, which are critical for recovering the full connectome. Scattering-based imaging provides access to the structure factor of three-dimensionally oriented fibers. By probing a fixed scattering angle under multiple azimuthal illumination angles, in-plane fiber orientations and crossings can be recovered using computational scattered light imaging (SLI). However, despite containing 3D information, a theoretical framework to extract full 3D orientations has been lacking. In this talk, a simple analogical approximation of Rayleigh-Gans scattering theory is introduced to extract the 3D orientation of nerve fibers from one-dimensional SLI measurements. The theory is validated using tilted microscopic glass phantoms consisting of 2 um-thick rod lattices fabricated by two-photon lithography. Finally, the method is applied to brain tissue samples and compared with 3D-PLI.
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All authors Dennis Scheidt, Charlotte Voß, Cristian Rosero Arias, Santiago Saavedra Castano, Felix Matuschke, Roxana Koojimans, Katrin Amunts, Arturo Susarrey-Arce, Markus Axer

Optics · Cross-listed from cond-mat.mes-hall

Generalized s-d model for Wannier-Mott excitons in layered magnetic semiconductors

Sonu Verma, Bashab Dey and Akashdeep Kamra

The recent discovery of excitons coupled to the magnetic order, and the consequent strong magneto-optic responses, in some van der Waals magnetic semiconductors has triggered intense activity at the interface of magnetism and semiconductor optics. Here, we present an analytically tractable minimal model that describes magnetic order, electrons, holes, and excitons within a unified framework, thereby capturing a wide range of phenomena. It treats the magnetic order and itinerant carriers to be comprised by distinct electronic orbitals that are mutually coupled via orbital-dependent onsite exchange, similar to the treatment of metallic magnets using an s-d model. Investigating CrSBr bilayer as a case study, we benchmark our model and its predictions against recent experimental and ab-initio results finding good agreement as well as new insights enabled by the model's simplicity. Examining the optical selection rules, we find the conservation of a quantum number formed from a combination of spin and layer pseudospin to be a useful guiding principle, even in noncollinear magnetic configurations. Our analysis finds a series of bright and dark excitonic states in such layered A-type antiferromagnets. The presented framework should be valuable in achieving intuitive understanding of recently discovered excitonic phenomena and guiding the discovery of other excitonic states in layered magnetic semiconductors.
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Optics

Machine learning-assisted design and explainable optimization of CdSnP2-based integrated solar-photodetector devices

Md. Alamin Hossain Pappu, Kazi Abrar Shafin, Mainul Hossain et al. (+1 more)

CdSnP2-based integrated solar cell-photodetector (SC-PD) devices employing CdS and CuGaSe2 (CGS) as the window and back surface field (BSF) layers, respectively are investigated using a hybrid machine learning (ML)-assisted SCAPS-1D framework. Device optimization is performed by varying the thickness, doping concentration, and defect density of individual layers. SCAPS-generated data are used to train six ML models and one deep learning model, with ensemble-based algorithms exhibiting the highest predictive accuracy. The ML-guided optimization identifies the n-CdS/p-CdSnP2 (CTP)/p+-CGS architecture as the optimum configuration among thirteen candidate structures. Incorporation of a 200 nm CGS BSF layer significantly enhances both photovoltaic and photodetection performance, increasing the efficiency from 20.67% to 32.69%, responsivity from 0.53 AW-1 to 0.72 AW-1, and detectivity from 2.51x1014 Jones to 1.78x1016 Jones. SHapley Additive exPlanations (SHAP) analysis reveales that band-offset engineering, particularly at the window/absorber and absorber/BSF interfaces, together with absorber properties, governs device performance. These findings demonstrate the potential of CdSnP2 and the proposed data-driven SCAPS-ML framework for the accelerated design of high-efficiency multifunctional optoelectronic devices.
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All authors Md. Alamin Hossain Pappu, Kazi Abrar Shafin, Mainul Hossain, Jaker Hossain

Optics

A Silicon-Compatible Uncooled Compact Broadband Infrared Spectrometer

A. Nomezine, G. Daligou, D. Vlassov et al. (+3 more)

Infrared spectroscopy is a widely used technique for molecular identification, yet its widespread deployment remains constrained by bulky instrumentation, cryogenic cooling requirements, and limited portability. Here we demonstrate broadband near- to short-wave infrared spectroscopy enabled by a silicon-compatible GeSn photodetector integrated into a compact digital micromirror device-based single-pixel architecture. By combining detector design with targeted optical reconfiguration and wavelength recalibration, we extend the operational range up to 2.4 micrometers while maintaining room-temperature, zero-bias photovoltaic operation. System-level benchmarking quantifies the intrinsic trade-off between spectral extension and detectivity in narrow-bandgap photodetection, yielding a specific detectivity of $1.12 \times 10^{10}$ cm Hz$^{1/2}$ W$^{-1}$ at 1.55 micrometers with an extended wavelength cut-off. We validate the capabilities of the obtained spectrometer through selective identification of representative commodity plastics, demonstrating a lightweight, low-power, and mechanically robust platform for portable and autonomous deployment. Despite the expected increase in generation-limited noise, access to strong polymer combination bands beyond 1.7 micrometers allows enhanced material discrimination. This work establishes a pathway toward scalable distributed molecular sensing and broadens access to infrared spectroscopy for environmental monitoring, industrial process control, and community-level chemical detection.
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All authors A. Nomezine, G. Daligou, D. Vlassov, S. Assali, M. R. M. Atalla, O. Moutanabbir

Optics

Vortex solitons in disclination quasicrystals

Hua Zhong, Yaroslav V Kartashov, Yongdong Li et al. (+2 more)

Being structures characterized by discrete rotational symmetry $\mathcal{C}_\nu$ of order $\nu$, photonic quasicrystals are capable to support stable propagation of linear vortex-carrying light beams and vortex solitons. However, the impact of discrete rotational symmetry $\nu$ of quasicrystals on the properties of vortex light states was not investigated so far, as only the systems constructed using the simplest Penrose tiling or corresponding optically induced Penrose lattices were considered in this context. Here we propose a broad class of quasicrystals with global topological defects – disclinations – introduced into their structure that allows to produce new quasicrystalline structures with any desired order of discrete rotational symmetry from basic Penrose structure. Such global topological deformation substantially enriches linear spectrum of quasicrystals, allowing them to support new types of linear vortex states and bifurcating from them families of stable thresholdless vortex solitons with unusual intensity and phase distributions. We found two different classes of stable vortex solitons consisting of in-phase or out-of-phase pairs of closely located bright spots, with total intensity distribution reflecting particular discrete rotational symmetry of the quasicrystal with disclination. Remarkably, even low-charge vortex solitons can be stable in quasicrystals with disclinations, while stability intervals for them broaden with decrease of the discrete rotational symmetry $\mathcal{C}_\nu$ of quasicrystal. Our results expand the theory of localization in quasicrystals to structures with global topological deformation, highlighting new prospects for robust transmission of power or information arising in these systems.
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All authors Hua Zhong, Yaroslav V Kartashov, Yongdong Li, Fangwei Ye, Yiqi Zhang

Wednesday 2 September

Optics

Grammar-based topology search for reconfigurable integrated photonic spectrometers

Juejun Hu

Reconfigurable integrated photonic spectrometers can generate exponentially increasing measurement states from a small number of switching elements, making them a promising design class for high-performance portable spectroscopy. However, selecting a circuit architecture remains largely intuition driven. We introduce a grammar-based topology optimization framework that composes standard photonic building blocks, canonicalizes and physically prunes candidate circuits, and jointly searches topology and component parameters using a coherent scattering-matrix model. Designs are screened by a decoder-independent architecture objective that combines absolute singular-value noise gain with multi-line conditioning, thereby accounting for response diversity and optical throughput. Direct held-out spectrum reconstruction confirms that this surrogate is a strong predictor of reconstruction quality at high incident signal-to-noise ratio (SNR). Across the nonresonant and resonator-augmented design spaces examined, dFT and its variants offer the best balanced performance; increased component loss favors a shallower dFT variant in which one differential-delay stage is replaced by an analog optical phase shifter. Passive and active rings provide no robust advantage attributable to resonant amplitude coding. The results identify balanced complementary interferometric responses, efficient terminal collection, and limited lossy circuit depth as central design rules, and establish a systematic route for selecting task-optimized photonic circuit topologies under technology-specific constraints.
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Optics · Cross-listed from quant-ph

Exponential speedup of polarization stabilization for long distance DWDM quantum networks

Jinyi Du, En Teng Lim, Xingjian Zhang et al. (+4 more)

Fibre-based quantum networks distributing polarization entanglement require a stable and uninterrupted transmission basis for reliable operation. Bright classical reference light enables rapid polarization feedback but can introduce noise into quantum channels. Entangled-photon-based feedback avoids this noise, but typically interrupts the target entanglement channel during calibration and becomes prohibitively slow over long distances due to the product loss of fibre links. Here, we overcome both limitations by combining wavelength-bracketed probing with switch-enabled path decomposition. Spectrally adjacent entangled-photon sidebands track the polarization response of the central distribution channel without interrupting its transmission, while optical switches and local reference fibres independently determine the signal and idler network transformations. Transferring the resulting compensation settings to the central channel eliminates calibration-induced downtime and changes the acquisition-time scaling from the product of the link losses to the sum of losses. We demonstrate the method on a 133 km fibre testbed and achieve continuous closed-loop stabilization for more than 24 hours without classical reference light. The decomposition of multi-link quantum feedback into single-link measurements provides a scalable stabilization strategy for wavelength-multiplexed quantum networks.
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All authors Jinyi Du, En Teng Lim, Xingjian Zhang, Hongwei Gao, George F.R. Chen, Dawn T. H. Tan, Alexander Ling

Optics

Optical Reservoir Computing with Structural Nonlinearity for Forecasting Chaotic Time Series

Leandro R. Venâncio, Jonathan Dong, Mickael Mounaix et al. (+1 more)

Optical computing offers a promising route to high-speed, energy-efficient information processing. However, implementing nonlinear operations typically requires strong light-matter interactions. Here, we introduce structural nonlinearity into an optical reservoir computing architecture, using only linear components. A digital micromirror device acts as a reconfigurable scattering potential, while the propagation of light through a scattering medium provides the high-dimensional mode mixing. By enforcing a second interaction with the wavefront shaper, we obtain a quadratic mapping of the input within the reservoir. A single experimental apparatus simultaneously implements conventional and structurally nonlinear reservoir architectures, enabling a direct comparison on forecasting of the chaotic Mackey-Glass time series. We demonstrate that the structurally nonlinear reservoir improves short-term prediction accuracy and better preserves the long-term dynamics of the chaotic system, demonstrating the potential of structural nonlinearity for low-power optical computing.
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All authors Leandro R. Venâncio, Jonathan Dong, Mickael Mounaix, Jacopo Bertolotti

Optics

Random-mapped intensity optical neural network: all-optical two-layer computing for multimodal optical-field inference

Gi-Hyun Go, Doeon Lee, Gookho Song et al. (+1 more)

Free-space optical neural networks offer distinct advantages for computational imaging and machine vision because they can compute directly on incident optical fields. However, conventional ONNs composed of cascaded linear optical components are bound to a general linear input-output relation with square-law detection between the input field $\mathbf{x}$ and output score $\mathbf{y}$, $\mathbf{y}=|\mathbf{T}\mathbf{x}|^2$, where at best every complex-valued element of the transmission matrix $\mathbf{T}$ is trainable. This restricts each output score to a quadratic form $\mathbf{x}^\dagger\mathbf{A}\mathbf{x}$ with rank-one decision matrix $\mathbf{A}=\mathbf{t}^\dagger\mathbf{t}$. Here, we present a random-mapped intensity optical neural network (RMI-ONN) as an all-optical two-layer computational network that lifts this rank-one limit. We numerically demonstrate that a high-dimensional feature projection by a disordered medium, a programmable nonnegative intensity mask, and segmented spatial power summation together can surpass the rank-one ceiling through the expressivity of higher-rank quadratic decision boundaries. Furthermore, exploiting the vectorial coherent wave-mixing nature of the disordered medium, we experimentally validate multimodal classification of amplitude, phase, and polarization on MNIST, Fashion-MNIST, and Quick Draw with the RMI-ONN, under a single optical configuration across all encoding domains. These results provide a practical and conceptual basis for scalable direct-field optical processors capable of exploiting amplitude, phase, and polarization information within a unified intensity-based inference framework.
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All authors Gi-Hyun Go, Doeon Lee, Gookho Song, Mooseok Jang

Optics · Cross-listed from cond-mat.quant-gas

Dynamical stabilisation of a quantum fluid using a single topological defect

Deborah Capecchi, Paolo Comaron, Antonio Gianfrate et al. (+5 more)

The size and shape of a quantum fluid in equilibrium is strongly influenced by the inter-particle interactions. In the attractive interaction regime, atomic quantum fluids ultimately collapse in a violent process that expels most of the particles from the macroscopically occupied state. Here, we use a quantum fluid of light in propagating geometry as an analogue to a two-dimensional Bose-Einstein condensate (BEC) with large attractive interactions to show that non-trivial topology significantly alters the dynamical behaviour of the collapse, enhancing the BEC stability and delaying the collapse time by an order of magnitude. We measure direct experimental signatures of topology affecting quantum hydrodynamics, unveiling the inherent competition between attractive nonlinearities, that lead to the collapse, and the preservation of topological charge from a multi-charged vortex. We fully characterise the collapse process in coordinate space and the eventual `solitonification' of the system and connect it to the mode structure of the excitation spectrum.
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All authors Deborah Capecchi, Paolo Comaron, Antonio Gianfrate, Milena De Giorgi, Dario Ballarini, Daniele Sanvitto, Franco Dalfovo, Dimitrios Trypogeorgos

Optics

Spatially-resolved multiphoton photoemission from a lateral transition metal dichalcogenide heterostructure

Lina Hansen, Paul Martin, Sai Shradha et al. (+7 more)

Transition metal dichalcogenides (TMDs) in their monolayer form offer a premier platform for next-generation optoelectronics, particularly through the local manipulation of their robust excitonic states using nanoscale electric fields. These localized states can be dynamically controlled through spatial structuring as well as through ultrafast field modulations driven by tailored optical pulses. Characterizing the resulting rapid, nanoscale charge carrier dynamics requires a technique with exceptional spatial and temporal resolution. Here, we report on the spatio-temporally resolved investigation of ground state and excited state photoemission from a lateral heterostructure built of monolayers of WSe$_2$ and MoSe$_2$ using few-cycle light pulses with a photon energy of 0.62 eV. We utilize photoemission electron microscopy to spatially resolve the highly nonlinear photoemission from the monolayer structure with few tens of nanometer resolution. By varying the laser pulse energy, we extract the nonlinearity of the photoemission process and thus the dynamic binding energy of the photoelectrons before and after optical excitation with high spatial and temporal resolution.
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All authors Lina Hansen, Paul Martin, Sai Shradha, Julian Picker, Arvid Klösgen, Kerstin Harland, Katrin Meier, Andrey Turchanin, Bernhard Urbaszek, Jan Vogelsang

Optics

Exceptional Topological Signatures of Non-Hermitian Photonic Hopf-Link Braids

Samit Kumar Gupta

Non-Hermitian physics endows the non-Abelian systems with exceptional topology characterized by non-commutative braid patterns. Interplay of distinct competing sources of non-Hermiticity may induce novel topological effects. Here, we provide a generalized Hatano-Nelson model with higher-order nonreciprocal hoppings, non-Abelian gauge fields, and staggered gain-loss processes showing the exceptional topological structure of the Hopf-link braids that undergoes a EP-mediated topological phase transition. We demonstrate that mixing multiple nonreciprocal channels drives the system into highly intricate, nested complex energy Hopf-link braids and expands the topological landscape up to higher-order braiding sectors. Furthermore, utilizing biorthogonal eigenvector tracking, we map the structural evolution of the exceptional phase boundaries via the maximum Petermann factor in the phase angle parameter planes. We show that the gain-loss non-Hermiticity drives a topological crossover where the extended exceptional contours constrict into isolated regimes. The demonstration of EP-mediated topological phase transition of Hopf-link braids and the associated rich exceptional phase portraits may offer new physical insights with promising applications in robust, fault-tolerant communication channels and quantum computing platforms.
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Optics

Comparative study of noise-like pulse emission from Mamyshev oscillator and conventional passively mode-locked fiber laser

Oumaima Ougrige, Florent Bessin and François Sanchez

We perform an in-depth comparison of noise-like pulse emission from Mamyshev oscillator and mode-locking through nonlinear polarization rotation (NPR) in fiber lasers. NLP's temporal and spectral characteristics are analyzed in both normal and anomalous dispersion regimes. The output coupling coefficient is modified to optimize the energy of the output pulses. It is demonstrated that the pulse energy is systematically higher in NPR-based mode-locking fiber lasers than in Mamyshev oscillators. This is due to the filtering effect in the Mamyshev oscillator which rejects ultrashort pulses whose energy is insufficient to successfully pass through the two shifted optical filters.
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Optics · Cross-listed from quant-ph

Single-Shot Fidelity Reveals Hard and Soft Limits: A Universal Yardstick for Photon-Number-Resolving Detectors

Tetsuya Tsuruta, Akio Yoshizawa and Daiji Fukuda

Photon-number-resolving (PNR) detectors are essential for photonic quantum computing, where a single measurement outcome must reliably herald a specific quantum state. However, detector fidelity is conventionally evaluated using ensemble-averaged statistics obtained from many measurements, which can remain high even when individual photon-number assignments are frequently misidentified. Here we introduce a universal single-shot fidelity that directly quantifies the probability of correctly identifying a photon number in a single measurement. The framework combines an efficiency-based POVM with a resolution-driven confusion matrix derived from the detector response, allowing photon loss and photon-number misidentification to be treated separately and then recombined into a single operational metric. This distinction reveals two fundamentally different limitations. Detection-efficiency loss represents an unrecoverable hardware constraint, whereas resolution-driven misidentification can be reduced by introducing a rejection region, trading generation rate for confidence. Because the metric is defined independently of detector architecture, it enables direct comparison between energy-resolving detectors such as transition-edge sensors and multiplexed click-based detectors on the same footing. Applying the framework to calibration data from three distinct detector architectures, we demonstrate quantitative comparison across photon-number regimes relevant to both discrete-variable and continuous-variable photonic quantum computing. The resulting benchmark provides a common operational metric for evaluating photon-number-resolving detectors and connecting detector performance to photonic quantum-computing requirements.
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Optics · Cross-listed from cond-mat.str-el

Prominent Dimensional Effects on High-order Harmonic Generation in Strongly Correlated Electron Systems

Kento Uchida, Shintaro Takayoshi, Yuta Murakami et al. (+6 more)

Dimensionality strongly affects elementary excitations in correlated quantum materials, yet its impact on extreme nonlinear optical responses remains largely unexplored. Here, we combine high-harmonic generation (HHG) experiments on quasi-one-dimensional SrCuO$_2$ and quasi-two-dimensional Pr$_2$CuO$_4$ with nonequilibrium simulations of Hubbard models. We find a pronounced dimensional contrast: SrCuO$_2$ exhibits a robust plateau-like high-harmonic spectrum with weak temperature dependence, whereas Pr$_2$CuO$_4$ shows a monotonic decrease in harmonic yield and strong thermal suppression, especially at higher harmonics. The simulations qualitatively reproduce these trends and identify dimensionality-dependent doublon–holon dephasing, governed by spin–charge coupling, as their microscopic origin. These results establish dimensionality and spin–charge coupling as key control parameters for extreme nonlinear optical responses in correlated insulators.
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All authors Kento Uchida, Shintaro Takayoshi, Yuta Murakami, Dongjoon Song, Alannah M. Hallas, Masayuki Watanabe, Takashi Konishi, Aiko Nakano, Koichiro Tanaka

Optics

Static and breathing dynamics of optical bullets in nonlinear GRIN fibers

Sonali Maity, Tiyas Das, Anuj P. Lara et al. (+2 more)

We explore the properties of spatiotemporal solitons within nonlinear graded-index (GRIN) optical fibers, specifically addressing their formation, stability, and breathing dynamics. We solve the (3+1)-dimensional nonlinear Schrödinger equation employing a semi-analytical variational approach, which leads to a set of reduced coupled ordinary differential equations describing the bistable bullet dynamics. The stability of these states is assessed using the Vakhitov-Kolokolov criterion and linear stability analysis within the Kantorovich optimization framework. The breathing dynamics of the optical bullets are investigated adopting the potential formalism, revealing an oscillatory behavior and self-imaging dynamics in GRIN fibers. The analytical results demonstrate strong agreement with full numerical simulations, validating the robustness of our theoretical model. Our research enhances the understanding of stabilizing self-repeated 3D optical structures, which is beneficial for the development of advanced photonic technologies.
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All authors Sonali Maity, Tiyas Das, Anuj P. Lara, Ashis Paul, Samudra Roy

Optics

Dispersion-engineered meta-coverslip for multimodal synthetic imaging

Yuchen Ma, Danlin Xu, Xinwei Wang et al. (+2 more)

Multimodal optical imaging provides comprehensive sample characterization but has traditionally been hindered by complex and bulky instrumentation. Here, we propose a dispersion-engineered meta-coverslip to seamlessly integrate bright-field, differential, fluorescence, and holographic imaging modalities within a standard microscope architecture, requiring no hardware modification or realignment. The meta-coverslip utilizes a scalable subwavelength multilayer film to engineer spatio-temporal dispersion for a customized high-dimensional transfer function. As an example, we demonstrate flexible switching among the four imaging modalities by simply tuning the illumination wavelengths. Lastly, we demonstrate that the synthesis of multimodal images can provide spatially registered structural and molecular information for more comprehensive biological analysis. Our approach provides an accessible, scalable, and flexible solution for advanced imaging and is extensible to other multiplexed optical systems in sensing and computing.
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All authors Yuchen Ma, Danlin Xu, Xinwei Wang, Guangwei Hu, Liangcai Cao

Optics · Cross-listed from quant-ph

A proposal for a hybrid free-space optical quantum communication network with hexagonal boron nitride-based single photon sources

Julien Chénedé, Mostafa Abasifard, Tjorben Matthes et al. (+2 more)

Hexagonal boron nitride (hBN) is known as a promising solid-state platform to host room temperature quantum emitters that produce high purity single photons. The bright and spectrally adaptable hBN emitters are space-compatible, making hBN well-suited for satellite-based free-space optical (FSO) quantum key distribution (QKD) at wavelengths where the atmospheric background is naturally suppressed. This paper presents a pathway to develop hBN emitters operating near the Ca-II Fraunhofer line (at 854 nm), enabling daylight FSO operation. Moreover, due to its compatibility with the first telecommunication window at 850 nm, it is possible to interface with optical fibers to bridge the `last mile' in a scenario where multiple end-users connect through a single optical ground station to a QKD satellite. We therefore introduce a concept that combines continuous operation of a quantum network, hybrid links to minimize deployment costs, and high data rates due to the use of realistic single photon sources. The realization would be an important milestone for the development of the quantum internet.
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All authors Julien Chénedé, Mostafa Abasifard, Tjorben Matthes, Asl{\i} Çakan, Tobias Vogl

Optics · Cross-listed from quant-ph

Observation of Hong-Ou-Mandel interference between photon and polariton

Yun-Ru Fan, Ying-Ao Su, Kai Guo et al. (+11 more)

Light-matter interactions underlie many quantum technologies, yet whether quasiparticles formed from such interactions preserve the full quantum state of light remains unresolved. Surface plasmon polaritons (SPPs), a class of polaritons formed by interacting photons with free-electron oscillations at metal-dielectric interfaces, are prime candidates to explore this question. Here we demonstrate quantum interference between single photons and SPPs using an Au-SiN$_{\mathrm{x}}$ integrated photonic-plasmonic device. Our results reveal that SPPs retain the indistinguishability of their excitation photons, establishing SPP as a viable quantum information carrier and opening a potential route toward photonic-plasmonic quantum circuitry.
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All authors Yun-Ru Fan, Ying-Ao Su, Kai Guo, Bo-Yu Fan, Yao-Qing Zhang, Hai-Zhi Song, Hao Li, Yong Geng, Kun Chen, Deng-Ke Zhang, Li-Xing You, Yan-Yu Wei, Guang-Can Guo, Qiang Zhou

Optics

Multidimensional Light Detection with Symmetry-engineered Heterojunctions

Yucai Lin, Yaoqiang Zhou, Ruijuan Tian et al. (+11 more)

Miniaturised multidimensional light detection, encompassing full-Stokes polarimetry and spectroscopy in ultracompact footprints, is attracting growing interest for its potential to capture a comprehensive set of light properties in portable platforms. Although significant progress has been made in miniaturised schemes for independent polarisation and spectral detection, achieving simultaneous high-dimensional light detection remains an outstanding challenge that limits their development toward full integration. We overcome this limitation by breaking the rotational and inversion symmetries in a symmetry-engineered van der Waals heterojunction to realise an ultracompact multidimensional photodetector. The dual symmetry breaking gives rise to non-trivial quantum geometric and topological features, enabling simultaneous broadband polarisation- and spectrum-resolved light detection, in contrast to previous van der Waals material-based devices, which could detect only one of these modalities. Our device, with an effective area of only 10 micron x 10 micron, reconstructs full-Stokes polarisation with overall root-mean-square errors below 0.05 and resolves spectral peaks separated by 0.4 nm, capabilities not previously achieved in single-pixel detectors. By unifying high-fidelity polarimetry and sub-nanometre spectroscopy in a single electrically tunable junction, our work eliminates the need for cascaded detection architectures and establishes a foundation for multidimensional detector arrays for integrated photonics, quantum information processing, and precision imaging.
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All authors Yucai Lin, Yaoqiang Zhou, Ruijuan Tian, Faisal Ahmed, Andreas C. Liapis, Youqiang Huang, Yawei Dai, Yuwei Chen, Weiwei Cai, Zongyin Yang, Weida Hu, Tawfique Hasan, Luojun Du, Zhipei Sun