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Physics Physics Optics

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Thursday 8 October

Optics

Learning qBIC Resonances across Metasurface Families in Dielectric Fourier Space

Shuangteng Lei, Li Yu, Tianxin Li et al. (+1 more)

Bound states in the continuum (BIC) metasurfaces are typically described by geometry-specific parameters, hindering cross-geometry comparison, while ultranarrow qBIC features are easily diluted in full-spectrum learning. Here, 2015 samples from seven dielectric metasurface families are mapped to a shared reciprocal-lattice grid, where two frozen low-order Fourier channels capture resonance shifts with mean within-branch $R^2$ values of 0.871-0.999. Field-level analysis of two representative branches further confirms that these shifts are consistent with the Maxwell-Fourier perturbation picture. A five-channel K-space backbone models the broadband spectrum, while a local complex K-space expert parameterizes the qBIC resonance through a differentiable Fano layer. The expert reduces resonance-position mean absolute error (MAE) from 3.2 to 0.95 nm and the resonance-depth error by 14-fold on a geometry-blocked test set. The same coordinate supports spectrum-to-structure reconstruction.
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All authors Shuangteng Lei, Li Yu, Tianxin Li, Wei Lu

Optics

Simulations of Fluorescence and Energy Transfer in Periodic Systems: Pitfalls and Considerations for Bound States in the Continuum

Ilia Lykov, Sergejs Boroviks and Olivier J. F. Martin

Bound states in the continuum (BICs) combine high quality factors with strong electromagnetic-field localization and are therefore widely explored for enhancing light–matter interactions. However, large field amplitudes do not directly translate into useful fluorescence enhancement or energy transfer enhancement between two donor–acceptor fluorophores. Here, we investigate this question for a hybrid plasmonic–photonic resonant waveguide grating supporting a symmetry-protected BIC. We emphasize some of the pitfalls associated with the numerical simulations, especially the utilization of periodic boundary conditions for fluorescence. Strong BIC-related fields can enhance acceptor absorption while useful fluorescence enhancement remains moderate. Extensive simulations and the comparison of different figures of merit, indicate that, while a BIC can suppress radiative leakage, it can also redirect a large fraction of the energy into Ohmic losses. As a result, the useful fluorescence enhancement of donors remains moderate, whereas absorption by acceptors can be strongly enhanced in Förster resonance energy transfer (FRET) experiments. It is essential to separate near-field FRET from long-range energy transfer and reabsorption mechanisms, both of which are mediated by the delocalized BIC mode. Finally, results obtained for finite gratings are compared with infinite periodic simulations and conceptual inconsistencies explained. This work provides a consistent framework for interpreting fluorescence, absorption, and energy transfer in BIC-based periodic nanophotonic systems.
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Optics

Inverse Design of Integrated Photonic Components for Visible-Light Applications

Christoph Stockinger, Marko Šimić, John O. Adeniran et al. (+3 more)

Photonic integrated circuits (PICs) operating in the visible spectral range are crucial for quantum technologies, optical sensing, and nonlinear optics applications. However, their development is hampered by limited integration density and operational bandwidth, linked to low refractive index contrast and restricted parameter space in intuition-based PIC design. We address these bottlenecks with an adjoint-based, fabrication-aware inverse design workflow tailored for visible-spectrum photonics. By expanding the capabilities of FDTDX, an open-source, GPU-accelerated FDTD solver, we provide a versatile memory and runtime efficient inverse design platform. Demonstrating this approach on a silicon nitride (Si3N4) platform, we design, fabricate, and experimentally validate ultra-compact, broadband components for light routing, multiplexing, and polarization control. This work provides a scalable framework for high-density, high-performance visible-light PICs.
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All authors Christoph Stockinger, Marko Šimić, John O. Adeniran, Natale G. Pruiti, Marc Sorel, Peter Banzer

Optics

Engineering Photon Avalanche Thresholds in Single Nanocrystals with Plasmonic Nanostructures

Marcin Szalkowski, Maciej Fryckowski, Małgorzata Misiak et al. (+3 more)

Optical sub-diffraction imaging has become an essential tool in modern research. Recently, a new imaging strategy has been demonstrated that exploits the strongly nonlinear excitation-emission response of rare-earth-doped nanocrystals operating in the photon avalanche (PA) regime. This approach benefits from simple optical instrumentation, near-infrared excitation and emission, low cytotoxicity, and high photostability. However, its practical implementation is hindered by relatively high (10-100s of kW/cm2) excitation power densities required to initiate the PA process. We aim to mitigate this limitation through electromagnetic field enhancement provided by metallic nanostructures. The results of microscopic studies of individual photon-avalanching nanocrystals coupled to a silver island film demonstrate a greater than tenfold reduction in the excitation power density required to trigger the avalanche emission. These experimental results, corroborated by numerical modelling, which elucidates the role of plasmon-mediated electromagnetic field enhancement in modifying the photon avalanche dynamics, paves the way towards new generation of low excitation power probes for sub-diffraction imaging and sensing.
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All authors Marcin Szalkowski, Maciej Fryckowski, Małgorzata Misiak, Artur Bednarkiewicz, Dawid Piątkowski, Sebastian Maćkowski

Optics

Impact of Stimulated Brillouin Scattering on Modulation Instability in Fiber Fabry-Perot Resonators

Alice Houard, Thomas Bunel, Matteo Conforti et al. (+2 more)

We report the experimental and numerical demonstration of stimulated Brillouin scattering-induced stabilization of Kerr-driven modulation instability in fiber Fabry–Perot resonators. We show that Brillouin scattering shapes the modulation instability spectrum into a stable multi–free-spectral-range cascade that is otherwise unstable in the absence of Brillouin effects. We further identify that this stabilization originates from the real part of the Brillouin response, leading to an asymmetric Kerr-Brillouin interaction governed by the relative position of the Brillouin frequency shift with respect to the cavity resonances. These results establish stimulated Brillouin scattering as an additional degree of freedom for controlling nonlinear dynamics in Kerr resonators.
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All authors Alice Houard, Thomas Bunel, Matteo Conforti, Saliya Coulibaly, Arnaud Mussot

Optics

Full-Vector Diffractive Deep Neural Networks

Shengmei Zhao, Gongyuan Wang, Zhiwan Wang et al. (+2 more)

Conventional diffractive deep neural networks (D2NNs) treat polarization as independent channels and rely on scalar or semi-vectorial propagation models, which neglect cross polarization coupling and vector diffraction. Here we propose a vector D2NN (V-D2NN) that embeds the full vector angular spectrum method into the end-to-end training pipeline. This physically rigorous framework describes vectorial light-matter interactions across cascaded diffractive layers, enabling direct optimization of polarization conversion, spin-orbit coupling, and vectorial interference without external polarization optics. We demonstrate the V-D2NN on polarization-multiplexed tasks–ector beam generation, polarization dependent imaging and classification, and multiple channel optical encryption–where it consistently outperforms scalar and semi-vectorial counterparts. In longitudinal-field engineering, the V-D2NN actively shapes a prescribed longitudinal field with a normalized correlation of 0.839, a capability inaccessible to scalar-propagation models. An open-source training framework is also provided to support further development of vectorial diffractive optics for computing, sensing, and communications.
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All authors Shengmei Zhao, Gongyuan Wang, Zhiwan Wang, Jianan Shao, Haolin Liu

Optics

Optical Signals Synthesized from an Optical Lattice Clock with Uncertainty of 1.3E-17

Yuan Yao, Jinpeng Zou, Haosen Shi et al. (+3 more)

We report an accurate optical frequency synthesizer, which can generate single-frequency laser light with high frequency stability and accuracy at desired frequencies over a wide optical region. The frequency of the output signal is divided from an 171Yb optical lattice clock via an accurate optical frequency divider based on an optical frequency comb. Therefore, the output of the optical frequency synthesizer inherits the frequency accuracy from the Yb optical clock. The frequency uncertainty of the 171Yb optical lattice clock is evaluated to be 6.8 mHz, corresponding to a fractional frequency uncertainty of 1.3E-17, mainly limited by the blackbody radiation shift and the lattice-induced light shift.
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All authors Yuan Yao, Jinpeng Zou, Haosen Shi, Hongfu Yu, Longsheng Ma, Yanyi Jiang

Optics · Cross-listed from cond-mat.str-el

Probing and Manipulating Quantum Materials with Strong-field Terahertz and Mid-infrared Radiation

S. J. Li, H. Y. Wu, S. J. Zhang et al. (+1 more)

Emergent phenomena in quantum materials arise from interactions among different degrees of freedom. Identifying these interactions and establishing their roles in ordered states are central problems in condensed-matter physics and provide a basis for controlling material properties. Many relevant low-energy excitations and gaps lie in the terahertz (THz) and mid-infrared (MIR) range, where intense phase-stable fields can both interrogate nonlinear dynamics and drive selected degrees of freedom far from equilibrium. This review surveys recent progress in probing and manipulating quantum materials with strong-field THz and MIR radiation, with emphasis on nonlinear electronic dynamics, collective-mode coupling, symmetry-sensitive responses and field-induced changes in electronic structure and ordered states. Particular attention is given to developments enabled by the Synergetic Extreme Condition User Facility (SECUF).
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All authors S. J. Li, H. Y. Wu, S. J. Zhang, Y. T. Li

Wednesday 7 October

Optics

Topological Spatiotemporal Mode-Locked Lasers

Xiaokang Lian, Yuchen Zhang, Mutian Xu et al. (+4 more)

Achieving robust high-dimensional solitons both in optics and Bose-Einstein condensates remains a great challenge, due to unpredictable high-order perturbations. Here we propose and demonstrate a novel topological spatiotemporal mode-locked fiber laser empowered by mode-division multiplexing, for precisely controlling of the spatiotemporal solitons. By introducing time delays between the individual transverse mode paths, a topological spatiotemporal lattice is formed in the multimode cavity, which in turn excites periodic spatiotemporal solitons. These solitons are stable against the perturbations, attributed to periodic potentials induced by the nonreciprocal dissipative coupling interactions. Moreover, under the thermodynamic limit, the solitons condense into nested-type spatiotemporal solitons, a phenomenon analogous to the Bose-Einstein condensate of matter waves. Our results indicate that topological spatiotemporal mode-locked lasers not only constitute a controllable source of robust spatiotemporal light bullets, but also provide a valuable platform for exploring nonlinear high-dimensional soliton dynamics and non-Hermitian topological physics.
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All authors Xiaokang Lian, Yuchen Zhang, Mutian Xu, Bing Han, Chengkun Cai, Jun Liu, Jian Wang

Optics · Cross-listed from quant-ph

Structured leakage in OAM-encoded qubits revealed by distributed quantum feature extraction

Yayu Mo, Nazifa Rumman, Sanjeev Shapkota et al. (+2 more)

Orbital angular momentum (OAM) modes have emerged as an important platform for high-dimensional quantum communication but remain vulnerable to environmental noise and channel imperfections. Here we introduce a logical-qubit representation of OAM propagation in which modes evolve as qubits through noisy quantum channels. In this representation, turbulence manifests as leakage from the logical OAM subspace into turbulence-induced leakage components, providing a unified description of degradation in both single-photon and coherent-beam regimes. We show that turbulence-induced leakage exhibits systematic dependence on turbulence strength and OAM order, revealing structured signatures of information redistribution beyond the logical subspace. Leveraging this insight, we develop a distributed quantum feature-extraction scheme that encodes high-dimensional OAM states into quantum representations and employs quantum convolutional operations to extract turbulence-robust features. Simulations and experimental measurements demonstrate robust extraction of these features across a broad range of turbulence strengths, OAM orders, and propagation conditions. Our results establish a direct link between OAM-channel dynamics, structured leakage, and quantum learning, providing a physics-informed framework for characterizing turbulence-degraded high-dimensional optical states and extracting robust signatures of turbulence-induced information redistribution.
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All authors Yayu Mo, Nazifa Rumman, Sanjeev Shapkota, Thomas A. Searles, Sanjaya Lohani

Optics

Optimal Diffractive Focusing of Vortex Beams

Roohollah Ghobadi, Carrie Rodriguez, Lukas Scarfe et al. (+2 more)

We formulate diffractive ring focusing of paraxial beams carrying orbital angular momentum (OAM) through a finite circular aperture as a variational optimization problem. For a fixed topological charge, we determine the real-valued radial pupil that maximizes the intensity at a prescribed ring radius and propagation distance under a normalization constraint on the input field. The resulting problem admits an exact analytical solution: the optimal pupil combines the familiar Fresnel phase structure with an OAM-dependent Bessel radial modulation, and the associated eigenvalue yields a rigorous upper bound on the achievable ring intensity. We further analyze the lens-assisted configuration and derive a simple bound that allows direct comparison between diffractive and refractive vortex focusing. The theory also provides a quantitative framework for evaluating the performance of practical mask designs, including binary Fresnel-Bessel zone plates and amplitude-weighted pupils. We have experimentally tested our predictions in the optical domain by implementing the corresponding vortex beam pupils and comparing their propagation and focusing performance with the optimal solution. Our results establish the vortex-beam analogue of optimal amplitude-only focusing and identify the fundamental limits governing diffractive concentration of structured waves
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All authors Roohollah Ghobadi, Carrie Rodriguez, Lukas Scarfe, Maxim A. Efremov, Ebrahim Karimi

Optics

Photoluminescence study of Vanadium in 4H- and 6H- Silicon Carbide

Ibrahim Boulares, Anne R. Evans, Jeremy L. Smith et al. (+1 more)

Point defects with optically addressable spin states are a key building block for quantum networks, but few solid-state emitters combine a spin-photon interface with emission in the low-loss telecommunications band. Vanadium (V4+) defects in silicon carbide (SiC) meet this requirement, emitting zero-phonon lines (ZPLs) throughout the telecom O-band in both the 4H- and 6H-SiC polytypes while retaining an addressable electron and nuclear spin system [1,2]. Although the orbital and spin structure of these defects has been characterized in detail, the polarization selection rules have not been fully mapped experimentally. Here we present polarization-dependent photoluminescence (PL) measurements of vanadium ZPLs in 4H- and 6H-SiC at cryogenic temperature, of two scattering geometries: edge and face-on (emission wavevector perpendicular and parallel to the crystal c-axis, respectively). Emission from two of the four {\alpha} sites, ({\alpha}2 and {\alpha}3) and the 6H-SiC {\gamma} sites, are polarized parallel to the c-axis ({\sigma}-polarized), whereas emission from {\alpha}1 and {\alpha}4 are polarized perpendicular to the c-axis ({\pi}-polarized). Additionally, we report preliminary, lower signal measurements of the e̱ta} sites.
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All authors Ibrahim Boulares, Anne R. Evans, Jeremy L. Smith, Brenda VanMil

Optics

Propagation-Invariant Transmission Eigenmodes in Weakly Scattering Media

J.C Osorio-Tascon and P. A. Quinto-Su

Propagation-invariant beams (PIBs) with annular angular spectra preserve their transverse intensity structure over extended propagation distances. Here, we investigate whether scattering invariant modes (SIMs) can simultaneously exhibit scattering and propagation invariance. We measure free-space and sample transmission matrices (TMs) in an orthonormal annular basis for weak, moderate, and strong scattering media and identify localized SIMs (LSIMs) whose angular spectra remain predominantly confined to one or a few neighboring rings. Under weak scattering, 75 of the 128 SIMs considered for annular localization satisfy this criterion, with LSIMs exhibiting Bessel-like propagation. Under moderate scattering, 25 LSIMs are recovered after filtering low-intensity spectral components, whereas none are found under strong scattering. Although increasing modal crosstalk progressively suppresses annular localization and nondiffracting behavior, SIMs retain higher transverse-intensity correlation over propagation than the Gaussian-like and Bessel beams in the moderate and strong regimes. These results show that annular localization enables SIMs to acquire propagation invariance when scattering is weak, whereas the enhanced propagation robustness of SIMs can persist even after this localization is lost.
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Optics

Lattice tuning of optical and mechanical interactions in gold nanodisk metasurfaces

Juan I. Sangiorgio, Diya Xie, Emiliano Cortés et al. (+2 more)

The interaction between neighboring plasmonic nanoparticles can modify their intrinsic optical and mechanical resonances, enabling collective responses to be controlled through the geometry of their arrangement. Periodic arrays therefore provide a means of controlling both electromagnetic and mechanical interactions through a common geometrical parameter, the lattice pitch. Joint control of these two channels is particularly useful for engineering how coherent mechanical excitations couple to the substrate and are optically read out at the nanoscale. Here, we investigate the optical and mechanical response of gold nanodisk metasurface patches on silica as a function of lattice pitch using two-color pump-probe spectroscopy and numerical simulations. Optically, simulations show that varying the pitch tunes a Rayleigh anomaly across the broad localized surface plasmon resonance of the nanodisks, producing a strongly asymmetric collective optical response. Pump-probe measurements further reveal a pronounced wavelength dependence of the optical readout of coherent mechanical vibrations. Mechanically, we investigate how coupling between the nanodisks and the substrate depends on the character of the nanodisk resonances. The intrinsic nanodisk modes exhibit markedly different sensitivities to the periodic environment. One remains nearly independent of pitch, whereas another undergoes a pronounced frequency shift mediated by elastic interactions through the substrate. Numerical simulations further reveal that a third nanodisk resonance couples resonantly to a lattice-selected acoustic mode, giving rise to an avoided crossing and mode hybridization. These distinct mechanical responses are governed by how efficiently each mode couples to near-surface elastic motion in the substrate. These results demonstrate that lattice periodicity can simultaneously tune optical sensitivity and substrate-mediated mechanical coupling, providing a versatile platform for tailoring nanoscale optomechanical responses in the GHz regime.
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All authors Juan I. Sangiorgio, Diya Xie, Emiliano Cortés, Gustavo Grinblat, Andrea V. Bragas

Optics

Lithography-free in situ photonic inverse design

Yiqi Zhao, Martin M. Stein, Fan O. Wu et al. (+6 more)

Inverse design has emerged as a powerful engineering approach in nanophotonics, leading to devices with unintuitive designs that extend beyond human intuition. However, inverse-designed devices have been limited by costly and time-consuming fabrication iterations, simulation-reality gaps, and the fixed nature of etched devices. Separately, programmable photonics has emerged as an approach to modify the function of photonic devices after fabrication; recent free-form programmable-photonic devices have been scaled to have many degrees of freedom, in principle providing platforms well-suited for programmably realizing inverse design of conventional linear-photonic functions. Here we demonstrate in situ training of a single free-form programmable-photonic device to achieve a variety of functions that each would have been implemented in separate devices in the conventional inverse-design paradigm. Our platform is a thin-film lithium niobate slab waveguide with full programmability over the refractive index of the two-dimensional slab, with a tuning range of up to 1.7e-3 for each of the 10^4 effective pixels. We demonstrate 4 x 4 Gaussian-mode permutations, 4 x 4 Hermite-Gaussian mode demultiplexing, and 8 x 8 Gaussian-mode permutations, with maximum crosstalk of -27dB, -13dB, and -13dB, as well as 4 x 4 matrix-vector multiplication. We further demonstrate engineering of spectral responses, showcasing both wavelength-independent operation throughout the 1500-1600 nm window and wavelength demultiplexing between 1310 nm and 1550 nm, with maximum crosstalk of -8.4dB. Since the device is reconfigured for each function after fabrication, the investment in device fabrication, characterization, and calibration can be amortized across the various photonic functions the device is ultimately used for.
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All authors Yiqi Zhao, Martin M. Stein, Fan O. Wu, Ryotatsu Yanagimoto, Benjamin A. Ash, Mandar M. Sohoni, Logan G. Wright, Tatsuhiro Onodera, Peter L. McMahon

Optics

Visibility function and Stokes parameter analysis for non-ideal quarter-wave plates in a polarization contrast scheme

Stepan Kupavskii, Roman Malikov, Sergey Dyakov et al. (+6 more)

The match of the fourth power of the normalized third Stokes parameter for a single non-ideal quarter-wave plate (QWP) and the visibility function of the polarization contrast measured using a polarimetric setup with parallel polarizers and two identical QWPs was examined and observed. The behavior of the Stokes parameters of a single QWP and the visibility function of the polarization contrast scheme were investigated theoretically using the Fourier-modal method (FMM) and described within the Jones matrix formalism. This analysis was then generalized to a realistic case, accounting for the transmission anisotropy, phase deviation, and misalignment of optical components from their ideal orientations. An analytical expression for the visibility function of the polarization contrast scheme in terms of the normalized Stokes parameters was derived, along with the asymptotic expansions in terms of small parameters representing the phase deviation, transmission anisotropy, and angular misalignment of the polarization contrast scheme. For the investigated silicon-grating-based QWP, good quantitative agreement between the FMM-calculated fourth power of the normalized third Stokes parameter, and the visibility function (FMM-calculated and experimentally measured) was demonstrated over almost the entire investigated frequency range of 200-700 GHz.
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All authors Stepan Kupavskii, Roman Malikov, Sergey Dyakov, Sergei Tikhodeev, Arseniy Gavrilov, Kirill Dzhikirba, Sofya Andreeva, Igor Kukushkin, Nikolay Gippius

Optics

Sub-shot-noise mid-infrared photothermal measurements using twin beams

Kazuki Hashimoto and Takuro Ideguchi

Mid-infrared photothermal (MIP) measurement probes refractive-index changes induced by mid-infrared (MIR) absorption using visible or near-infrared light and has recently emerged as a powerful modality for MIR spectro-imaging in the life sciences. Reducing measurement noise allows the probe power to be lowered without compromising the signal-to-noise ratio (SNR), thereby mitigating the risk of sample damage. However, even in the absence of classical noise, the SNR of conventional MIP measurements using a classical coherent probe is fundamentally limited by shot noise. Here, we demonstrate sub-shot-noise MIP measurement using twin beams generated through seeded optical parametric amplification. Balanced detection of the twin beams suppresses the noise by more than 5 dB below the shot-noise level established using a coherent beam. As a proof-of-principle demonstration, we measure the MIP signal from liquid water using balanced twin-beam detection and achieve an SNR enhancement of more than 2 dB over the balanced coherent-beam detection.
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Optics

Thermal Holography with Nonlocal Metasurfaces

Mingze He, Lin Jing, Michele Guizzardi et al. (+7 more)

Thermal radiation and luminescence are among the most ubiquitous sources of light, yet their properties are difficult to engineer due to their incoherent nature. Recent advances in thermal emission control have endowed heat-generated light with spatial and temporal coherence, as well as control over its polarization, by judiciously patterning periodic arrays of nanostructures. However, custom wavefront engineering of incoherent light has remained an open challenge, as it requires not only sufficient spatial and temporal coherence but also arbitrary local phase control, which experimentally translates into sustaining long-range lattice resonances in aperiodic systems while maintaining their robustness against local phase perturbations. In this work, we address this longstanding limitation and demonstrate programmable vectorial control over the thermal emission wavefront from single-layer aperiodic nonlocal metasurfaces, realized by manipulating local geometric phases across a collective delocalized resonance. We exemplify the wavefront-shaping capabilities of our approach by demonstrating thermal beam steering, spin-momentum-locked thermal focusing and the generation of a thermal vectorial hologram, providing custom spatial and spectral control over thermal light. Our platform addresses challenges in thermal emission engineering and provides a route for light generation and control without the need for external coherent sources or bulky setups. Future work may extend this design principle to other incoherent emission systems, such as photo- and electroluminescence.
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All authors Mingze He, Lin Jing, Michele Guizzardi, Shixiong Yin, Martina Riva, Yajun Gao, Shuwei Guo, Adam C. Overvig, Sander A. Mann, Andrea Alù

Optics

Start-to-end simulations of non-relativistic electron acceleration along reflective grating structure by front-tilted laser pulse

I.V. Beznosenko, A.V. Vasyliev, S.M. Kovalov et al. (+2 more)

A comprehensive (start-to-end) simulation was performed regarding the formation of a front-tilted laser pulse and the subsequent acceleration of non-relativistic electrons moving along a reflective grating structure. The laser pulse tilt was formed using another diffraction grating – either reflective or transmissive. The pulse had a spectral range (FWHM) of 803–863 nm and an initial duration of approximately 17 fs. Acceleration under normal laser pulse incidence was also calculated for comparison. Research results indicate that the use of a femtosecond laser pulse with a front, tilted by means of a reflective diffraction grating, significantly enhances the efficiency of laser acceleration of non-relativistic electrons compared to the case of a pulse at normal incidence. Furthermore, it was found that using a transmissive diffraction grating to shape the tilted pulse front also increases acceleration efficiency relative to normal incidence on the accelerating grating, although the acceleration rate is lower than when a reflective diffraction grating is used.
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All authors I.V. Beznosenko, A.V. Vasyliev, S.M. Kovalov, R.R. Kniaziev, G.V. Sotnikov

2610.10193 · 7 Oct · 10 pages, 6 figures, 2 tables. Start-to-end PIC simulations of non-relativistic electron acceleration along a reflective grating structure driven by a front-tilted femtosecond laser pulse; comparison of pulse-front tilting by transmissive vs. reflective diffraction gratings

Abstract PDF $LASR ×6

Optics · Cross-listed from quant-ph

Beyond Spectroscopic Strong Coupling: Operational Benchmarks for Cavity-to-Magnon Quantum Transfer

Huang Xinyi, Zhang Xiang and Zhao Dongxing

Normal-mode splitting reveals coherent cavity–magnon hybridization but does not certify finite-time quantum-state transfer. We describe quantum transfer in a passive, linear cavity–magnon system coupled to thermal reservoirs as a thermal-loss channel specified by its coherent transmissivity $\eta$ and output-referred thermal population $\nu$. For single-rail qubits, we calculate the phase-corrected average fidelity and compare it with the deterministic measure-and-prepare benchmark of $2/3$. A Bell pair shared by the cavity and an isolated reference retains reference–magnon entanglement if and only if $\eta>\nu$. An input squeezed vacuum of strength $r$ yields sub-vacuum magnon fluctuations if and only if $\nu<\eta(1-e^{-2r})/2$. When the initial magnon and both reservoirs have the same occupation, an analytically determined peak-transmissivity time optimizes all three tasks. These task-dependent benchmarks show that a conventional linewidth-based strong-coupling criterion does not guarantee quantum-transfer performance. Conversely, entanglement or squeezing can survive below that spectroscopic reference when the added noise is sufficiently low. These benchmarks provide quantitative targets for transfer timing and thermal-noise control in intracavity-to-magnon quantum interfaces.
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Optics

Enhanced Magneto-Optical Kerr Effect in Nano-Magnetic Metamaterials with Near-Perfect Coherent Absorption

Xiaofei Xiao, Tingjun Zheng, Alex Vanstone et al. (+6 more)

The ability to control magnetic systems without external magnetic fields has attracted attention recently, with all-optical magnetic switching showing increasing promise. Gaining fine control over light-matter interactions in magnetic nanostructures is essential for advancing opto-magnetic technologies, but remains challenging because strong optical coupling must be achieved within ultrathin magnetic structures at the target wavelength. Here, we show that coherent optical interference can increase this interaction in patterned magnetic metasurfaces. Arrays of permalloy nanomagnets are placed on a thin dielectric spacer above a reflective back-plane, forming a magnetic metasurface whose reflected wavefront is defined by the nanomagnet geometry, fill factor, and spacer thickness. Destructive interference between the metasurface and back-plane reflections yields near-perfect absorption, exceeding 95% for circular nanomagnet arrays in both simulation and experiment. The absorbed power is dissipated almost entirely within the nanomagnets, with only a few percent lost in the metallic back-plane. Enhanced absorption is also accompanied by a stronger magneto-optical Kerr effect, driven by both increased light-nanomagnet interaction and reduced reflected background. These results provide a general approach for achieving high optical absorption and strong magneto-optical response in nanoscale magnetic systems, supporting advances in optically addressable spintronics, magnetic sensing, and all-optical magnetic control.
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All authors Xiaofei Xiao, Tingjun Zheng, Alex Vanstone, Daniel S. Bromley, Holly Holder, Kilian D. Stenning, Jack C. Gartside, Will R. Branford, Rupert F. Oulton

Optics

Bogoliubov-de Gennes spectrum, Cherenkov radiation and recoil of solitons with third-order dispersion underlying optical analogue horizons

Hasan Oguz

Third-order dispersion turns the soliton of the nonlinear Schrödinger equation, which underlies optical analogues of event horizons in fibers, into a weakly radiating solitary wave. We compute three of its properties without assuming a thermal emission law. First, the linearized (Bogoliubov-de Gennes) problem must be posed about the stationary state of the dispersive equation: linearizing about the integrable profile produces a complex quartet that is converged in grid and box, grows as the square root of the dispersion strength and is spurious. About the stationary state, on a periodic grid, the zero-mode sector consists of two Jordan blocks of size two and the spectrum is real at the operating point, including negative-energy box modes of the resonant branch. Second, we measure the steady Cherenkov emission of adiabatically prepared solitons from the flux of the radiation behind them, over eight decades. The radiation is phase-matched in the frame of the drifting soliton, and the first-order rate falls short of the measured one by factors of 29 to 45. Expressed through a scaled dispersion coefficient of the local soliton, the measured rate describes launched solitons of three amplitudes; with norm and momentum balance, and no further fitted parameter, it reproduces their recoil and the slow decay of their loss rate; at weak dispersion the loss of a launched soliton is the shedding of its launch mismatch. Third, a census of the asymptotic channels shows that long-wavelength upstream emission requires the chemical potential of the soliton, lowered by the comoving-frame Doppler shift of a drifting soliton, to lie inside the analysis band, which bounds the soliton amplitude. In a kinematic model of the flow the surface gravity has a closed form; the thermal relation and the entanglement built on it are imposed inputs of that model. The construction applies to Raman-free Kerr media.
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Optics · Cross-listed from quant-ph

Efficient detection of spectral cluster states

M. Kalash, U.-N. Han, C. Roh et al. (+3 more)

Multimode entangled states of light are key resources for high-dimensional photonic quantum technologies, particularly for continuous-variable quantum computing and quantum information processing. Exploiting their full capabilities requires detection strategies that can efficiently and simultaneously access a large number of modes and their quantum correlations. Multimode optical parametric amplification (MOPA) provides a promising approach by amplifying multiple quadratures prior to detection, rendering the measurement robust against subsequent optical losses while enabling broadband operation. Here, we demonstrate the spectral multimode capability of MOPA by simultaneously characterizing a broadband 60-node dual-rail continuous-variable cluster state. We reconstruct the cluster-state nullifiers across the spectral modes and observe nearly uniform squeezing ranging from -7.2 to -6.5 dB. Furthermore, by evaluating the van Loock-Furusawa criterion across all relevant bipartitions, we verify genuine multipartite entanglement throughout the 60-node state. These results establish MOPA as a promising platform for scalable high-dimensional quantum information processing in the spectral domain.
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All authors M. Kalash, U.-N. Han, C. Roh, M. H. M. Passos, Y.-S. Ra, M. V. Chekhova

Optics

Phonon-Enabled Collective Strong Coupling of Color Centers in a Plasmonic Cavity

Bharti Garg, Prabhdeep Singh, Masoud Taleb et al. (+1 more)

Quantum emitters in hexagonal boron nitride (hBN) are promising building blocks for solid-state quantum photonics because of their bright room-temperature emission. These emitters strongly interact with lattice vibrations, which partially underpins their excitation efficiency. Here, using complementary cathodoluminescence (CL) and photoluminescence (PL) spectroscopy, we demonstrate cavity-mediated interactions between hBN quantum emitters coupled to the same plasmonic Au void cavity at the room temperature. Cathodoluminescence measurements reveal that a vibronic transition of the 443 nm emitter hybridizes with the cavity mode, giving rise to a spectrally resolved splitting, while the neighboring 537 nm emitter remains in the weak-coupling regime despite spectral overlap. The energy split of the CL peak is at the order of 36.2 meV, whereas the PL-resolved peak is approximately 24.1 meV, which is due to the collective excitations of multiple emitters per electron excitation and their mutual interactions. Maxwell-Bloch simulations reproduce the experimental spectra and identify the observed splitting as the result of cavity-induced hybridization. Excitation-dependent PL further shows that the hybridized state can be accessed through phonon-assisted excitations below the zero-phonon transition. These results demonstrate that vibronic transitions provide an effective pathway for controlling interactions between multiple quantum emitters in hybrid plasmonic nanophotonic systems.
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All authors Bharti Garg, Prabhdeep Singh, Masoud Taleb, Nahid Talebi

Optics

Angular resolution limit of augmented reality waveguides from guided mode theory

Guohua Wei

We derive the angular resolution limit of an augmented-reality (AR) waveguide combiner from guided mode theory. A slab of finite thickness supports only a discrete set of total-internal-reflection (TIR) angles, giving an angular resolution that worsens with thinner waveguides and smaller TIR angles. At 500~$\mu$m thickness the resolution is worse than the 1 arcmin (60 ppd) acuity target over most of the usable TIR range, and reaching 1 arcmin for TIR < 42$^\circ$ requires a substrate thicker than 1 mm. The limit is washed out by a source linewidth above $\sim$0.1~nm or a thickness variation above $\sim$100~nm across the pupil-replication period, but only partially by pupil truncation and not at all by out-coupling loss. LED- and micro-LED-based displays are therefore unaffected, owing to their broad spectra, whereas a narrow-linewidth laser-based display in a thin, uniform waveguide is subject to this limit.
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Optics

Vector beams for real-time monitoring of crystalline symmetry on {\mu}m length scale

Yongbo Lv, Zidu Yu, Haotian Zhang et al. (+2 more)

Symmetry constrains and determines the physical properties of crystalline solids. Determining crystalline symmetry often requires large-scale diffraction facility and advanced analysis software and therefore cannot be realized with real-time feedback. Alternatively, optical anisotropy has also been exploited for elucidating the rotation, mirror and inversion symmetries of solids on smaller tabletop setups. Second harmonic generation, in particular, has demonstrated a remarkable sensitivity to subtle changes in these symmetries during phase transitions. To access the full nonlinear susceptibility of a crystal in a cryogenic or vacuum environment, angle-by-angle rotation of the scattering plane of an obliquely incident and outgoing beam in co-ordination with their polarization states is required. This typically results in a bulky and wobbly setup, significant feedback latency, and a focal spot size > 20 {\mu}m unsuitable for microscopic samples such as few-layer 2D materials. In this work, we make use of vector beams to realize a non-rotating oblique-incidence setup, demonstrating a real-time (> 10 fps) visualization of crystalline symmetry on a sample area of ~ 2 {\mu}m in diameter. Both the feedback latency and focal spot size represent more than an order of magnitude improvement over previous designs based on a Gaussian beam and mechanically-rotating stages. Here, the use of a vector beam greatly simplifies and reduces the cost of nonlinear optical anisotropy measurements, heralding widespread applications of this approach in both research and industrial settings, for example, for strain monitoring and crystal alignment. Our work may also promote broader integration of structured optical field into solid state and condensed matter research in the future.
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All authors Yongbo Lv, Zidu Yu, Haotian Zhang, Liejia Qian, Hao Chu

Optics

Electromagnetic Field of an Oscillating Point Charge Measured by a Transversely Comoving Observer

Ruben Canora and Shengwang Du

We investigate the electromagnetic field produced by a harmonically oscillating point charge and measured by a spatially separated observer undergoing the same motion. We evaluate the exact retarded field on the observer's worldline and project the electromagnetic field tensor onto the observer's local orthonormal tetrad. This construction yields the electric and magnetic fields, electromagnetic energy density, and Poynting vector measured as functions of the observer's proper time. Our formulation separates unambiguous local observables from the observer-dependent classification of a field as radiation and provides a concrete setting in which to examine how a charge that is spatially static in a non-inertial coordinate system can nevertheless produce time-dependent locally measured fields.
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Optics

Compact Fully Integrated Alignment-Free and Linearly Polarized Ho$^{3+}$ Single-Frequency Waveguide Laser

Jeswin Jacob, T Toney Fernandez, Dale Otten et al. (+3 more)

We report, for the first time, a fully integrated Ho$^{3+}$-doped fluoride glass waveguide laser incorporating a femtosecond laser-inscribed waveguide and waveguide Bragg grating. The compact 12.4 mm cavity achieves stable single-frequency lasing at 2062.21 nm with a line width of better than 5 MHz. The laser emits linearly polarized light, which is efficiently delivered through an SM1950 single-mode fiber. This alignment-free architecture provides a compact and robust platform for integrated mid-infrared single-frequency laser sources.
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All authors Jeswin Jacob, T Toney Fernandez, Dale Otten, Ori Henderson-Sapir, 3 Karen Privat, David Lancaster

Optics

Electromagnetically Transmissive and Thermally Opaque Engineered Microwave Interconnect

Md. Jawad Ul Islam, Ishrat Jahan, Abdelrahman Omar et al. (+3 more)

In a standard two-conductor microwave transmission line, both the signal trace and the wide ground plane act as parasitic heat leakage paths along the propagation direction. To prevent this heat leakage, we devised a single-conductor microwave interconnect: the ground plane is removed entirely and the remaining signal trace is periodically fragmented into physically isolated metallic islands. We show that despite the galvanic isolation between adjacent metal islands, a surface confined mode of specific symmetry, the odd-symmetric spoof surface plasmon polariton, propagates through this periodic, single-conductor medium. This odd symmetry imposes an electromagnetic field null at the waveguide centerline, allowing complete removal of the metal at periodic intervals along the single-conductor waveguide without impacting EM propagation. Measurements on fabricated prototypes confirm the transmission response despite the physical fragmentation of the conductor, with de-embedded propagation loss of ~0.0031 dB/mm across a 5-6.5 GHz passband. Time-domain characterization verifies 1 Gbps amplitude-modulated data transmission with less than 145 ps group delay variation. Coupled electro-thermal simulation yields an effective thermal conductivity of 0.336 W/m*K, a 40x reduction relative to a continuous microstrip line of identical footprint.
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All authors Md. Jawad Ul Islam, Ishrat Jahan, Abdelrahman Omar, Md. Omar Faruk Noman, Md Zunaid Baten, Soumitra R. Joy

Tuesday 6 October

Optics

Shadow-Free Scattering with Complex Frequency Excitations

Vitali Kozlov, Wei Wang, Seunghwi Kim et al. (+2 more)

The optical theorem dictates that the wave scattering of an object in the forward direction is proportional to the total power extinguished from the excitation. For passive objects, this relationship is a by-product of the intuitive notion that scattering and absorption necessarily create shadows, and that zero forward scattering, i.e., no shadow, can only be obtained if the object is fully transparent, i.e., it neither scatters nor absorbs. Materials with gain can be in principle leveraged to suppress forward scattering while preserving a large scattering signature in other directions. However, sufficient optical gain is challenging to realize, and it inherently leads to instabilities and nonlinearities. Here, we experimentally demonstrate shadow-free \ scattering from a passive high-index dielectric sphere by exciting it with a complex frequency signal tailored to mimic the presence of material gain. We achieve as much as 26dB suppression of the forward scattering when compared with optimal monochromatic excitations, while preserving strong scattering in other directions. More broadly, our results demonstrate how complex frequencies offer a natural pathway to enhance control over the scattering signature of passive objects, with implications for a range of photonic applications.
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All authors Vitali Kozlov, Wei Wang, Seunghwi Kim, Arno Thielens, Andrea Alu