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Physics Physics Optics

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Tuesday 22 September

Optics

Metalens-transparent ultrasound transducer module for extended depth photoacoustic microscopy

Krishnendu Samanta, Myunghoo Lee, Shubham Mirg et al. (+5 more)

Optical-resolution photoacoustic microscopy (ORPAM) provides label-free optical-absorption contrast at millimeter-scale tissue depths with micrometer-scale lateral resolution. However, its volumetric coverage is limited by the short depth of focus of conventional optical lenses, whereas system miniaturization is constrained by bulky optics and ultrasound transducers. Here, we present an extended-depth ORPAM system that combines an ultra-thin metalens for optical excitation with a planar transparent ultrasound transducer (TUT) for photoacoustic detection. Fabricated from piezoelectric lithium niobate, the chip-scale TUT provides ~80% optical transparency and enables coaxial optical excitation with simultaneous acoustic detection at 14.4 MHz center frequency. This architecture eliminates the need for bulky acousto-optic combiners and large-volume acoustic coupling arrangements between the transducer and imaging target. We evaluate three ultra-thin metalens designs as hyperbolic, quadratic, and extended depth-of-focus (EDOF), which provide effective axial ranges of 0.3, 0.8, and 1.3 mm, respectively, with lateral resolutions of 1.1 micron for hyperbolic, 1.2 micron quadratic lenses, and 1.5 micron for EDOF across the full axial range. Phantom experiments demonstrate improved visualization of multilayered, inclined, volumetrically distributed targets with the EDOF design compared with the two other metalenses. Label-free imaging in awake, head-fixed mice further demonstrates that EDOF provides extended-depth visualization of subcortical microvasculature without being subjected to anesthesia-induced confounds. This chip-scale metalens-TUT architecture provides a foundation for developing compact photoacoustic microscopy systems.
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All authors Krishnendu Samanta, Myunghoo Lee, Shubham Mirg, Zhihao Zhou, Saniya Patil, Johannes E. Fröch, Arka Majumdar, Sri-Rajasekhar Kothapalli

Optics

Structural Resilience of Space-Time Wave Packets to Volumetric Scattering

Kefu Mu, Hsiao-Chih Huang, Chen-Ting Liao et al. (+1 more)

Optical space-time wave packets (STWPs) can be engineered to sustain tight transverse confinement over long distances. However, whether the requisite precise spatiotemporal correlations underlying this behavior survive volumetric scattering remains unclear. Here, we experimentally demonstrate that STWP light sheets with transverse thicknesses of 11 and 22 microns largely retain their prescribed spatiotemporal structure after transmission through 10 mm thick scattering phantoms (scattering coefficient = 0.84 per mm). Moreover, compared with size-matched Gaussian beams, STWPs exhibit greater preservation of their initial spectral intensity distribution across the prescribed space-time domain following scattering. Additionally, the transmitted STWPs remain tightly confined and preserve on-axis intensity decay rates similar to those of their unscattered counterparts. As the scattering conditions span biologically relevant regimes, the structural and propagation resilience of STWPs to scattering highlights their potential for extended-depth 3D biomedical microscopy.
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All authors Kefu Mu, Hsiao-Chih Huang, Chen-Ting Liao, Hui Min Leung

Optics

Temporal Interfaces in Metamaterials with Shape-Varying Inclusions

Ishtiaque Rahman, Mohamed Hesham Mostafa and Viktar Asadchy

Temporal modulation of metamaterials is commonly achieved by varying constituent material properties, while changes in meta-atom geometry offer an additional means of controlling their effective response. Here, we develop an analytical and numerical framework for temporal scattering in metamaterials composed of cylindrical inclusions undergoing abrupt geometric transformations. Changing the radius of circular cylinders modifies the filling fraction and scalar in-plane effective permittivity, enabling temporal reflection, field amplification or attenuation, and frequency conversion. An area-preserving transformation from circular to elliptical cross sections introduces anisotropy, producing angle-dependent temporal scattering and redirecting the energy flow while conserving the wavevector. We derive these effects using effective-medium theory and temporal boundary conditions and compare the predictions with full-wave time-domain simulations. The simulations reproduce the main scattering and temporal-aiming trends, with larger angular deflections than predicted by the quasistatic model at higher permittivity contrasts. This suggests that moving toward the resonant regime may offer opportunities for stronger temporal aiming. These results identify inclusion geometry as a means of controlling wave amplitude, frequency, and energy-flow direction at temporal interfaces.
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Optics

Structured detection beyond spatial imaging

Bruno K. Nowak and Shu-Wei Huang

In a point-scanning microscope, detection through a pinhole improves resolution and replacing the pinhole with a detector array provides redundant encoding of the object spectrum, enabling correction of nonidealities in the imaging system or further resolution improvements, for instance. Here, we show that the mathematical principles underlying structured detection are not intrinsically spatial and therefore structured detection may be used for imaging distributions in other physical domains, such as time, frequency, and velocity space. We numerically illustrate this generality by applying structured detection to an electromagnetic distribution in time using four-wave mixing (FWM). The resulting image reconstructions outperform the temporal equivalent of confocal detection, even as the FWM models are made more realistic and shot noise is considered.
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Optics · Cross-listed from quant-ph

Fluctuation-Driven Nonlinear Amplification of Quantum Statistics

Yuewei Song, Zhenghe Zhou, Shuai Wan et al. (+9 more)

Photon statistics have moved to the forefront of modern optics, as intensity fluctuations and correlations shape multiphoton interactions and reveal information beyond mean-intensity measurements. Developing high-quality photon sources with pronounced correlations is a fundamental necessity in these fields. Here we demonstrate fluctuation-driven nonlinear statistical amplification of quantum light in spontaneous four-wave mixing using filtered amplified spontaneous emission (ASE). Extending the coherent-pump framework to fluctuating fields, we show how nonlinear weighting of pump intensity combines with bosonic bunching to amplify quantum statistics and reshape temporal correlations. In a SiN microring, ASE pumping increases the zero-delay unconditional second-order correlation from 2.01 to 7.58 and extends the Hanbury Brown–Twiss correlation time by a factor of approximately 2.4. The super-bunched quantum source nevertheless retains heralded single-photon behaviour with $g_H^{(2)}(0)\simeq0.04$, while the same ASE pump supports time–energy entanglement in a silicon waveguide with a raw Franson visibility of 89.84%. These results establish driving-field statistics as a design dimension for quantum light, broadening the horizons for research into higher-order correlations and nonlinear physics.
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All authors Yuewei Song, Zhenghe Zhou, Shuai Wan, Hecheng Wang, Jinpeng Li, Bowen Liu, Yinhai Li, Chunhua Dong, Guangcan Guo, Chong Wang, Zhiyuan Zhou, Baosen Shi

Optics · Cross-listed from cond-mat.mtrl-sci

Superfluorescence as a cooperative amplifier of hidden anisotropy in a ferroelectric hybrid perovskite

Changhao Gao, Daniel Sandner, Talia Ruhrberg Estévez et al. (+4 more)

Superfluorescence (SF), intense picosecond bursts from self-synchronizing dipoles, is promising for room-temperature quantum sources. Yet, whether this synchronization can convert weak structural anisotropies into robust macroscopic order remains an open question. Here, we demonstrate that polycrystalline ferroelectric 2D perovskite thin films exhibit strongly linearly polarized SF with a degree of polarization (DOP) up to 86%. Remarkably, macroscopic polarization emerges without external bias despite randomly oriented microscopic domains, suggesting a cooperative gain mechanism that amplifies weak local anisotropies by several orders of magnitude into coherent, linearly polarized light bursts. Our results establish cooperative superfluorescence as a general concept for translating microscopic anisotropy into robust macroscopic order, exemplified here for linear polarization, offering a sensitive probe of hidden material symmetries and a framework for polarized quantum light sources
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All authors Changhao Gao, Daniel Sandner, Talia Ruhrberg Estévez, Jeron Timmer, Sophia Klubertz, Martijn Kemerink, Felix Deschler

Optics

Channeling defect emission through topological Jackiw-Rebbi states in hBN

Hugo Quard, Sergei Nedić, Nika Teran et al. (+4 more)

When two photonic structures of different topology are joined, an optical mode appears at their junction. Its existence depends only on this topological difference and not on the precise dimensions of either structure. Here we realize the photonic analogue of a Jackiw-Rebbi (JR) state in hexagonal boron nitride (hBN) hosting negatively charged boron vacancies, optically addressable spin defects. Two partially etched gratings, in which the order of the radiating and dark band-edge modes is reversed, are joined side by side. Angle-resolved reflectivity and photoluminescence reveal this reversal and a non-dispersive JR state at the junction. The state proves remarkably tolerant: despite fabrication errors of up to 20 nm, its wavelength lies within a 1 nm of the design, as predicted by a systematic numerical tolerance analysis. JR gratings therefore offer a robust, monolithic platform for controlling the emission of luminescent defects.
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All authors Hugo Quard, Sergei Nedić, Nika Teran, Otto Cranwell Schaeper, Xiaoying Huang, Shery L. Y. Chang, Igor Aharonovich

Optics

Reducing ringing artifacts in Wiener deconvolution using implicit physical priors

Jakub Czuchnowski and Jerome Mertz

With advances in high-speed imaging there is a growing need for robust high-speed deconvolution algorithms. Wiener deconvolution remains one of the fastest and simplest algorithms available, however it suffers from ringing artifacts that can limit its applicability. In this work, we develop two complementary, computationally efficient heuristic methods to suppress these ringing artifacts by using physical non-negativity and sparsity priors.
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Optics

Resolution-matched gain in Multi-beam ptychography

Runqing Yang, Maik Kahnt and Pablo Villanueva-Perez

Single-beam ptychography (SBP) requires overlapping scan positions for reliable reconstruction, and imaging larger areas demands more measurements. Multi-beam ptychography (MBP) illuminates several regions simultaneously, but its measurement gain at a fixed resolution remains unclear when diffraction intensities from different beams overlap on the detector. Using numerical simulations, we determined the minimum number of patterns needed to reach a target resolution by varying the scan step size for SBP and fully overlapped MBP with up to 15 beams. We define gain as the pattern count for repeated SBP scans divided by that for MBP at the same total imaged area and achieved resolution. Although the required MBP pattern count increased approximately linearly with beam number, it remained below that of repeated SBP scans. At 67% of the spatial Nyquist frequency using a one-bit threshold, fully overlapped MBP achieved a gain of approximately two. Detector cropping and lower-resolution targets reduced this gain, showing its dependence on usable diffraction information and the reconstruction criterion. Because overlapping intensities provide no spatial identification of individual beam contributions, this gain is a conservative benchmark; separation on the detector offers a route to larger gains.
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Optics

Optical-Memory Transport Imaging: Extension to Stochastic Diffusion

Haichun Liu and Jerker Widengren

Finite-memory optical tracers can encode transport properties through their previously experienced excitation. Using such memory features, harboured in the population of excitable long-lived electronic states within the emitters, instantaneous localization assessments are not needed to determine their transport properties. Here we formulate this principle for monitoring of stochastic transport extracted from transport-history integral over conditional transport histories. Under structured illumination, this history yields a measurable transfer-function response from which scalar and tensor diffusion are reconstructed without time-resolved acquisition. Fisher-information analysis identifies the optimal operating regime and yields first-principles, parameter-free predictions of scalar and tensor reconstruction precision, in quantitative agreement with independent Monte Carlo simulations. These results establish finite optical memory as a general principle for stochastic transport imaging.
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Optics

Orthogonal Flatbands-Enabled Robust Fano Resonances through Brillouin-Zone Folding

Yangsong Ye, Hanchuan Chen, Shijie Kang et al. (+8 more)

Fano resonances based on coherent interference between localized Lorentz modes and Fabry-Perot radiation continua have been widely explored for microwave metamaterial sensors, filters, and photonic devices. However, conventional Fano metasurfaces suffer from angular dispersion and polarization-dependent spectral variations, limiting robustness under dynamic illumination. Here, we propose a band-folding-enabled flatband engineering strategy to realize robust Fano resonances in a planar microwave metasurface with a 2x2 enlarged cell of orthogonally arranged H-shaped metallic resonators. The enlarged cell induces Brillouin-zone folding, generating a nearly dispersionless flatband near 15.3 GHz with suppressed momentum dependence and enhanced photonic confinement. This flatband state provides a high-Q localized resonance strongly coupled to the FP radiation continuum, producing a stable asymmetric Fano response. Furthermore, the orthogonal resonator configuration supports two polarization-decoupled dipole modes with comparable excitation efficiency, reducing polarization-induced spectral distortion. Near-field measurements and simulations verify localized flatband features, while far-field experiments demonstrate stable Fano responses under oblique incidence from 0{\deg} to 30{\deg} with minor resonance variation. A temporal coupled-mode theory model is developed to quantitatively describe Fano spectral evolution under different illumination conditions. This work establishes a flatband-mediated route toward robust microwave Fano metasurfaces and offers a general strategy for stable resonant photonic device design.
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All authors Yangsong Ye, Hanchuan Chen, Shijie Kang, Haitao Li, Ken Qin, Boyuan Ge, Xiexuan Zhang, Jingrong He, Jiusi Yu, Xiaoxiao Wu, Chunlei Yang

Optics · Cross-listed from quant-ph

Universal Fidelity Law for Linear-Optical Entangling Gates

Haim Nakav and Ofer Firstenberg

Imperfect photon sources degrade the performance of interference-based linear-optical entangling gates. We derive a universal fidelity law for these gates in terms of two standard source metrics: Hong-Ou-Mandel visibility and second-order coherence. We model the multiphoton component as an arbitrary overlap between noise and signal photons. While different values of the signal-noise overlap produce different error structures, associated with different physical platforms, all result in the same fidelity law. We test the model on our actively synchronized CNOT-gate experiment and against published results across different platforms, with no free parameters. This framework turns source characterization into a unified benchmark for photonic quantum computing.
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Optics · Cross-listed from nlin.PS

Is there an accelerating nonspreading wave packet in the Schrödinger equation with higher even-order dispersions?

Farrell Theodore Adriano and Hadi Susanto

Probably not. For Airy-type initial data, although nearly all lobes accelerate, the principal lobe remains essentially stationary. Moreover, the overall wave packet gradually disperses.

Optics

Meta-Optics-Based Diffractive Learning Machine for Angle-Multiplexed Multi-Task Processing

Mingcheng Luo, Jianmin Xiong, Jiayong Peng et al. (+4 more)

All-optical diffractive neural networks (DNNs) offer low latency, low energy consumption, and massive parallelism. However, their scalability in terms of network scale and multi-task processing remains limited. Here, we experimentally demonstrate a large-scale metasurface-based diffractive learning machine for angle-multiplexed multi-task processing. Our system employs a metasurface-based reflection cavity to realize a five-layer DNN comprising 115 million fixed, untrained diffractive nodes within a compact volume of 216 mm^3. By integrating this large-scale, untrained DNN with a lightweight, trainable digital backend containing only 7,680 parameters, our system experimentally achieves an accuracy of 95.3% on the standard full-scale CIFAR-10 dataset, significantly outperforming previous optical neural networks and rivaling large-scale digital models. Using a novel incident-angle-multiplexing scheme, our system experimentally achieves parallel processing of 11 tasks with negligible performance degradation, representing the largest multi-task processing capacity reported to date. Our work provides a scalable and energy-efficient solution for high-performance edge computing.
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All authors Mingcheng Luo, Jianmin Xiong, Jiayong Peng, Jingtian Hu, Hongwei Chen, Chester Shu, Chaoran Huang

Optics

Intra-bandgap Bound-State Magnonics in a Photonic Crystal Waveguide

Chong-Xin Run, Xue-Feng Pan, Bang-Yao Wu et al. (+5 more)

Cavity and waveguide magnonics have recently emerged as frontiers for investigating light-matter interactions. In these systems, coupling magnons into meticulously engineered photonic lattices with rich band structures provides a promising platform for tailoring magnon-photon interactions. However, how these hybrid interactions behave in the bandgaps of photonic lattices—specifically, the formation of magnon-photon bound states (MPBSs)—remains largely unaddressed. Crucially, these bound states arise through a mechanism that is fundamentally distinct from bound states in the continuum (BICs). Here, we experimentally demonstrate intra-bandgap bound-state magnonics by coupling yttrium iron garnet (YIG) spheres to a microwave photonic crystal waveguide. At room temperature, we observe MPBSs featuring highly tunable spatial localization, power-dependent interaction modulation under microwave pumping, and long-range magnon-magnon interactions mediated by mode overlap. These unique features bridge fundamental insights into intra-bandgap light-matter interactions with practical applications, offering an avenue for scaling up coherent networks and investigating many-body physics through engineered interactions.
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All authors Chong-Xin Run, Xue-Feng Pan, Bang-Yao Wu, Kai-Min Hsieh, Wei-Min Zhou, Anton Frisk Kockum, Peng-Bo Li, Io-Chun Hoi

Optics · Cross-listed from quant-ph

Post-selected enhancement of phase sensitivity in a two-path interferometer

Ryuya Fukuda, Katsuki Tanaka, Masataka Iinuma et al. (+1 more)

Post-selected metrology can exceed the standard quantum limit of single photon interference by concentrating all of the available Fisher information in a subset of post-selected outcomes. Here we apply this principle to a standard two-path interferometer, activating the Fisher information concentrated in the low probability output port by transferring the phase sensitivity to the circular polarizations of the photon. We obtain a phase gradient of the post-selected interference fringe that corresponds to that of a four-photon NOON state, providing a direct comparison of the performance of multi-photon interference with single-photon post-selection.
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All authors Ryuya Fukuda, Katsuki Tanaka, Masataka Iinuma, Holger F. Hofmann

Optics

Orbital Optical Chirality as the Origin of Vortex Dichroism

Yoshito Y. Tanaka and Keiji Sasaki

Optical chirality quantifies the geometrical twisting of electromagnetic fields and underlies chiral light-matter interactions, yet its conventional formulation captures only the spin-associated chiral geometry of light. We introduce orbital optical chirality and derive its continuity equation, revealing physical properties distinct from those of angular momentum. For vortex beams, spin and orbital optical chiralities follow the spin and orbital indices, respectively. Applied to a twisted nanorod dimer, orbital optical chirality gives rise to vortex dichroism through quadrupolar hybridized modes, while dipolar modes exhibit only circular dichroism. These results establish a unified framework for optical chirality and provide access to chiral geometries beyond those resolved by spin optical chirality alone.
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Optics

Momentum-Space Planar Optics for Long-Range Spin Hamiltonians

Huaqiang Li, Junxu Liu, Guangfeng Wang et al. (+3 more)

Evaluating spin Hamiltonians with dense, long-range interactions requires repeated global summation over many pairwise couplings, making energy evaluation costly on conventional electronic hardware. Here, we realize a planar optical architecture that evaluates such interaction energies directly in momentum space. For translationally structured couplings, the interaction kernel is encoded in the spatial transmission of a subwavelength-thick planar optical element placed in the Fourier plane. Pointwise spectral weighting followed by total-power detection reduces the quadratic spin Hamiltonian to a single optical signal, avoiding repeated digital multiply-accumulate operations during energy evaluation. We experimentally apply this approach to frustrated finite-range models and fully connected spin systems with oscillatory long-range couplings. The measured energies agree closely with numerical calculations, while optical annealing reproduces low-energy configurations and landscape statistics, reaching a normalized solution quality of 99.9%. These results establish momentum-space planar optics as a compact physical computing primitive for global-interaction problems in statistical physics and optimization.
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All authors Huaqiang Li, Junxu Liu, Guangfeng Wang, Erez Hasman, Xianfeng Chen, Bo Wang

Optics · Cross-listed from quant-ph

Efficient Ion-Photon Quantum Interface with Long-Working-Distance Exceeding 26 mm

Jungwoo Choi, Inhyuk Oh, Chanyang Im et al. (+2 more)

Trapped-ion quantum networks rely on efficient ion-photon interfaces, while objective-based free-space collection systems must balance high photon collection with sufficient working distance for practical integration with ion-trap hardware. Here, we design and characterize an ion-photon interface with a long working distance of 26.15 mm and a high numerical aperture of 0.5. The core of the interface is a photon-collection objective consisting of six commercial spherical lenses with optimized spacing. The interface achieved an overall fiber-coupled photon-detection efficiency of (1.29$\pm$0.09)% from the ion to the detector and maintains fiber coupling over several hours without active realignment, supporting stable operation of the ion-to-fiber interface. Photon-correlation measurements show clear antibunching in the fiber-coupled fluorescence, confirming the preservation of non-classical photon statistics. These results demonstrate a practical implementation of a long-working-distance photon collection interface for trapped-ion quantum network experiments.
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All authors Jungwoo Choi, Inhyuk Oh, Chanyang Im, Gibeom Son, Junki Kim

Optics

Photonic half-semimetals with dual semimetal-insulator topology

Zi-Xuan Gao, Xiaohan Cui, Xiao-Dong Chen et al. (+6 more)

Topological wave systems have largely evolved along two distinct paradigms: gapless topological semimetals and gapped topological insulators. While topological semimetals support bulk transport, they generally lack intrinsic selectivity among propagation channels; topological insulators enable robust transport but confine it to narrow interfaces, limiting spatial utilization. Here, we theoretically demonstrate and experimentally realize time-reversal-invariant spin-valley photonic half-semimetals (HSMs), which exhibit a dual semimetal-insulator topology within a single bulk band structure. In HSMs, the bandgap closes selectively in spin-valley space: for a given spin (valley), one valley (spin) is semimetallic while the other remains insulating. This coexistence of spin- and valley-resolved gapless and gapped band structures makes HSMs fundamentally distinct from both conventional semimetals and insulators. As a defining bulk phenomenon, an HSM functions as a spin-valley-locked beam splitter, intrinsically enabling valley-selective spin routing. Moreover, when four complementary HSMs are assembled into a periodic superlattice, the same dual topology enables reciprocal spin-valley-resolved multilane helical transport with 100% spatial utilization. These results establish HSMs as a platform for selective bulk wave control and multichannel topological transport beyond conventional topological phases.
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All authors Zi-Xuan Gao, Xiaohan Cui, Xiao-Dong Chen, Ke-Yi Zeng, Hao-Chang Mo, Xin-Tao He, Ruo-Yang Zhang, C. T. Chan, Jian-Wen Dong

Optics

Resonant multi-harmonic acousto-optics for programmable frequency control of visible light in a CMOS platform

Jacob M. Freedman, Matthew J. Storey, Daniel Dominguez et al. (+3 more)

Scaling quantum control for atoms, ions, and solid-state emitters requires gigahertz-frequency spectral control of high-power visible light in a volume-manufacturable platform. Silicon nitride photonics provides high power handling and CMOS-foundry compatibility but has no intrinsic mechanism for high-speed modulation. Integration with piezoelectric materials enables acousto-optic phase modulation, and mechanical resonant enhancement has made it efficient at gigahertz frequencies. However, a single resonance restricts the modulation waveform to a single tone, imposing Bessel-function sideband amplitudes and limiting frequency-shifting efficiency to 33.9%. Here we engineer a silicon nitride acousto-optic microstructure to support harmonically spaced resonances at 1.14 GHz and 2.28 GHz, each strongly optomechanically coupled to a 730 nm guided optical mode, so that tailored non-sinusoidal modulation waveforms can be resonantly synthesized. By piezoelectrically controlling the two mechanical amplitudes and their relative phase, we demonstrate 50% conversion to one sideband (1.5x the single-tone theoretical maximum), a flat seven-line comb, and a frequency shift with 60 dB carrier and 53 dB image suppression - to our knowledge the highest reported for an integrated modulator. The devices are fabricated in a 200 mm CMOS foundry, and we measure 91.7% yield without post-fabrication tuning across 36 devices from three wafers. We also show how the technique can be straightforwardly scaled to three or more harmonics. This result overcomes the trade-off between resonant enhancement and spectral programmability, with important consequences including improved single-qubit gate efficiency for hyperfine qubits.
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All authors Jacob M. Freedman, Matthew J. Storey, Daniel Dominguez, Andrew Leenheer, Nils T. Otterstrom, Matt Eichenfield

Monday 21 September

Optics

Topological Edge States Enable Step-like Power Transfer for Robust Arbitrary-Ratio Power Splitting

Jihwan You, Jibaek Song, Seungyong Lee et al. (+1 more)

Topological edge states offer a robust route to photonic devices and systems that remain functional despite structural imperfections. Topological waveguide arrays have been shown to deliver robust coupling, but only for full power transfer between the two edge waveguides—a robust route to an arbitrary intermediate ratio has remained unknown. Here we show that the topological edge states of a finite Su-Schrieffer-Heeger chain, realized with only four identical waveguides, form an arbitrary-ratio power splitter whose ratio is robust to both the device length and fabrication errors. Two near-degenerate edge supermodes beat to produce a step-like power transfer with a flat, length-insensitive plateau, in contrast to the sinusoidal transfer of a conventional directional coupler. The splitting ratio at this plateau is governed by the difference between the two waveguide gaps, making it immune to correlated fabrication offsets. We derive this behavior analytically and confirm it numerically and experimentally on a conventional silicon-on-insulator platform. Beyond this device, our analysis can be applied to general topological waveguide arrays, while the robust splitter offers a practical building block for fabrication-tolerant photonic circuits.
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All authors Jihwan You, Jibaek Song, Seungyong Lee, Sangsik Kim

Optics · Cross-listed from quant-ph

Strong coupling of a reconfigurable ${}^{171}$Yb atom array to a tunable telecom-band nanofiber cavity

Hideki Ozawa, Neville Chen, Yusuke Hisai et al. (+13 more)

Nanophotonic cavities provide strong atom-photon coupling in a compact, directly fiber-coupled geometry, while a reconfigurable array of $^{171}$Yb atoms combines high-fidelity gates with a metastable qubit state coupled directly to a telecom-band transition, making the two a natural interface between neutral-atom quantum processors and telecom quantum networks. Here, we realize strong atom-cavity coupling on the ${}^{3}\mathrm{P}_0 \leftrightarrow {}^{3}\mathrm{D}_1$ transition of ${}^{171}\mathrm{Yb}$, establishing, to our knowledge, the first neutral-atom cavity-QED system to reach the single-atom strong-coupling regime on a telecom-band atomic transition. Reflection spectroscopy of a single-sided cavity yields a single-atom internal cooperativity of $C_{\mathrm{in}}=5.6(1.0)$ and collective coupling following $\sqrt{N}$ scaling up to $N=5$ atoms, with homogeneous coupling at antinodes over $\sim$200 $\mathrm{\mu}$m along the nanofiber. Thermal tuning of a fiber Bragg grating provides in situ control of the cavity outcoupling rate over two orders of magnitude from the undercoupled to the overcoupled regime, relevant for various atom-cavity protocols. We confirm compatibility with reconfigurable atom arrays by demonstrating 99.95(6)% imaging fidelity and trap lifetimes comparable to free-space array, at 1 $\mathrm{\mu}$m from the nanofiber axis. Moreover, the diameter-engineered antireflection design of the nanofiber enables tweezer-based atom transport across the nanofiber with no measurable loss or heating at 4.5 $\mathrm{\mu}$m above the nanofiber, supporting a two-layer architecture for the nanofiber-integrated atom array. From the demonstrated atom-cavity coupling, atom capacity, and cavity mode profile, we project time-multiplexed remote atom-atom entanglement generation at 40 kHz, with prospects for further scaling through technical enhancements and channel multiplexing.
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All authors Hideki Ozawa, Neville Chen, Yusuke Hisai, Shunichiro Hashimoto, Kenichi N. Komagata, Remi T. Oddon, Shanjou Yang, Seitaro Horikawa, Seigo Kikura, Shigehito Miki, Takao Aoki, Tadayuki Yoshitake, Hideki Konishi, Shinichi Sunami, Akihisa Goban, Ryotaro Inoue

Optics · Cross-listed from quant-ph

Localized Decoherence as a Constructive Tool: An Optical Simulation of Matter-Wave Interference

Hadis Torbatiyan, Bedir Halc{\i}, Adrian Udovičić et al. (+2 more)

Decoherence is conventionally regarded as a detrimental process that suppresses quantum coherence and limits the performance of quantum technologies. Contrary to this view, we show that spatially localized decoherence can instead be exploited as an interferometric tool. Beyond its conceptual implications, localized decoherence provides a novel approach to prepare arbitrary macroscopic spatial superpositions for testing quantum physics with massive particles. We demonstrate the proof of principle by making use of the correspondence between optics and matter-waves through the equivalence of the respective propagation functions. By employing stochastic phase fields to the optical counterpart to model the decoherence, our experiments confirm the expected interference. The results establish localized decoherence as a resource for quantum state engineering.
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All authors Hadis Torbatiyan, Bedir Halc{\i}, Adrian Udovičić, Lara Ulčakar, Rainer Kaltenbaek

Optics

Spin-multiplexed terahertz image edge detection based on extrinsic chirality in all-dielectric metasurface

Yuxin Tang, Shichao Zhao, Li Luo et al. (+3 more)

Extrinsically chiral metasurfaces can exhibit pronounced chiral responses in planar structures without intrinsic chirality, making them attractive for spin-selective light manipulation. Here, we propose a transmissive all-dielectric terahertz metasurface for image edge detection. Owing to the extrinsic chiral response, the metasurface enables edge-enhanced imaging under right-handed circularly polarized incidence near 0.69 THz, while preserving bright-field imaging under left-handed circularly polarized incidence. Spatial-frequency analysis shows that the effective numerical aperture of the device is approximately 0.4, indicating the terahertz image edge detection can be achieved over a broad spatial-frequency range. This work provides a new design route toward transmissive terahertz all-optical image processing with spin selectivity and a large numerical aperture.
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All authors Yuxin Tang, Shichao Zhao, Li Luo, Tingting Tang, Hang Xu, Jie Li

Optics

Fisher-information training of optical sensing front ends from natural fluctuations

Abhinav Sinha and Kai Wang

Fisher-information-based optimization of programmable optical front ends in situ generally requires a response model or parameter-labeled measurements. We show that natural parameter fluctuations can instead provide the training signal. We construct proxies for the Fisher information (FI) of one parameter and the prior-weighted FI spectrum of multiple parameters from measured covariances after subtracting conditional detection noise, assuming locally affine responses. We use simulated photon counts from two incoherent point sources to train a mode sorter that approaches the quantum limit for separation and the Nagaoka–Hayashi single-copy bound for joint centroid–separation estimation. We demonstrate count-only updates that require no instrument response model and achieve performance comparable to model-based gradients. Our results provide a route to adaptive optical measurements without controlled parameter scans.
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Optics · Cross-listed from quant-ph

Overcoming the Hong-Ou-Mandel interference limitation for the second photon from a two-photon cascade

Raphael Joos, Michal Vyvlecka, Tim Strobel et al. (+8 more)

Quantum emitters such as semiconductor quantum dots can provide entangled photon pairs emitting from a system of cascaded states. However, the resulting temporal correlation between the two photons from the three-level ladder system has been shown to set a limit on the achievable two-photon interference. In this work, we show that such limitation, for photons emitted by the second transition, is only due to reduced temporal overlap at the interference beam splitter. We investigate this theoretically and experimentally by determining time-resolved four-photon coincidences between two successively emitted photon pairs. Post-emission synchronization shows the recovery of maximum interference visibility; in prospective quantum networks this could be achieved via deterministic quantum memories.
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All authors Raphael Joos, Michal Vyvlecka, Tim Strobel, Benjamin Breiholz, Furkan Aglarci, Ponraj Vijayan, Hans-Georg Babin, Arne Ludwig, Michael Jetter, Simone L. Portalupi, Peter Michler

Optics

Collective cavity quantum electrodynamics in solid-state optical clocks

Karen Mamian, Georgy A. Kazakov, Thorsten Schumm et al. (+1 more)

Solid-state frequency standards are generally limited by strong decoherence, rendering conventional interrogation schemes inefficient. The $^{229}$Th nuclear clock provides a unique and timely platform for solid-state optical metrology and nuclear cavity quantum electrodynamics (QED), featuring a coherence time many orders of magnitude shorter than the radiative lifetime in current experiments. Here, we propose and analyze three cavity QED-enhanced clock interrogation schemes that turn this timescale mismatch into an advantage, leveraging collective coupling of thorium nuclei to nanophotonic modes to enable fast interrogation and detection despite the long population lifetime. We reveal the central role of collective cooperativity in determining the clock frequency instability, and derive the optimal conditions (power, working-point detuning, thorium density) for clock operation.
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All authors Karen Mamian, Georgy A. Kazakov, Thorsten Schumm, Charles Roques-Carmes

Optics

Non-Hermitian mode locking in an L-band monolithic InP dual-ring laser

Xiao Sun, Mohanad Al Rubaiee, Jue Wang et al. (+4 more)

Coupling between laser cavities provides a means of controlling optical modes through their gain, loss, and hybridization. Here we demonstrate electrically controlled mode locking in a monolithic InP dual ring laser operating in the L band without a dedicated saturable absorber. Independent biasing of the two rings accesses single mode emission, mode locking, and hybridized supermode operation, with a measured intermode beat frequency of 542 MHz in the latter regime. The laser generates 7.9 ps pulses at 18.11 GHz. A coupled cavity model describes how differential nonlinear detuning modifies the modal gain loss contrast, and time domain simulations yield pulse durations and spectral widths close to those measured experimentally. In a device incorporating saturable absorbers, reverse bias enables 3.1 ps pulses and reduces the integrated timing jitter from 9.06 to 2.46 ps relative to the unbiased condition. These results connect electrical control of coupled-cavity states with picosecond pulse generation in a monolithic InP semiconductor platform for high repetition rate optical communications and microwave photonics.
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All authors Xiao Sun, Mohanad Al Rubaiee, Jue Wang, John H. Marsh, Stephen J. Sweeney, Anthony E. Kelly, Lianping Hou

Optics

Broadband Single-Particle Absorption Circular Dichroism Reveals Chiroptical Heterogeneity in Gold Helicoids

Rohit B. Raj, Susanna Bertuletti, Jeong Hyun Han et al. (+7 more)

Quantitative measurements of absorption circular dichroism (CD) at the single-particle level are essential for understanding how individual chiral nanostructures dissipate optical energy, yet broadband absorptance measurements remain experimentally challenging. Here, we introduce a wavelength-tunable integrating-sphere microscope that determines the absorptance of individual nanoparticles under right- and left-circularly polarized illumination through direct optical energy balance, enabling broadband measurement of the absorption dissymmetry factor, gabs. Measurements of achiral gold nanospheres and strongly anisotropic gold nanorods establish the apparent absorption CD baseline and demonstrate minimal detectable linear-dichroism-to-circular-dichroism (LD-to-CD) leakage under the experimental conditions. Applying this approach to 87 chiral gold helicoids synthesized using L-glutathione (L-helicoids) and 96 synthesized using D-glutathione (D-helicoids) reveals mean particle-level gabs values of opposite sign, with a statistically significant difference between the two populations. Individual particles nevertheless exhibit pronounced heterogeneity in response sign, magnitude, spectral position, and line shape. More than one-third of the particles in each population display opposite-sign absorption CD responses relative to their population-average tendency. Correlative SEM analysis of the L-helicoid population further shows that opposite-sign responses persist among isolated particles exhibiting the characteristic projected helicoid morphology, indicating that aggregation and gross differences in projected morphology are insufficient to explain the observed heterogeneity. These results establish broadband single-particle absorption CD spectroscopy as a direct probe of absorptive chiroptical heterogeneity and reveal particle-specific responses obscured by ensemble averaging.
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All authors Rohit B. Raj, Susanna Bertuletti, Jeong Hyun Han, Sepin Cho, Debapriya Pal, Nick Feldman, Ki Tae Nam, Willem L. Noorduin, A. Femius Koenderink, Erik C. Garnett