Optics · Cross-listed from quant-ph
Frame dependence of Kochen-Specker contextuality for relativistic spin systems
Jonte R. Hance and Ruben Campos Delgado
We ask whether Kochen-Specker contextuality is Lorentz invariant. On the full
Hilbert space, it is, since boosts act unitarily. Restricted to
spin, it is not: momentum acts as an environment applying momentum-dependent Wigner rotations, leaving
spin observables unsharp and breaking the operator identities behind state-independent contextuality. For
spin $1/2$ one scalar governs the loss, the packet average $\Delta$ of $\sin^2(\theta_W/2)$ (where $\theta_W$ is the Wigner angle); for any
spin, a ray degrades at a rate set by its
spin variance transverse to the boost. In the
spin-only account, the Free Will
Theorem's
SPIN axiom fails for every $\Delta>0$; the Yu-Oh set loses contextuality between $\Delta\approx0.008$ and $0.016$, with state independence going first; the Peres-Mermin square loses contextuality at $\Delta\approx0.059$ or $0.074$ by orientation; singlet CHSH loses nonlocality for $\Delta\geq0.159$; and a GHZ-state OR gate loses Raussendorf's contextuality certificate at $\Delta\approx0.206$. A $q$-plate implements the channel exactly on
photon polarisation, with a retardation in place of the rapidity, so the nonlocality, GHZ and aimed-source results are testable without motion.
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Optics
Energy-selective control of noise-assisted multipulsing by weak optical seeding in the dissipative-soliton-resonance regime
Vladimir L. Kalashnikov, Alexander Rudenkov, Evgeni Sorokin et al. (+1 more)
We study pulse-number selection in a
stochastic cubic–quintic complex Ginzburg–Landau model of a weakly seeded, normal-dispersion
laser in the dissipative-
soliton-resonance (DSR) regime. Without noise, a single pulse and pulse pairs persist at the same control parameters, and the total energy of an $N$-pulse state follows a ladder constructed from the single-pulse branch. The final energies of noisy trajectories lie close to the same ladder. Multipulsing therefore does not necessarily lose the single-pulse solution. It can reflect which coexisting state the noisy dynamics reaches. Optical seed injection suppresses energy-dependent multipulsing and, at larger seed power, produces a nonmonotonic DSR energy window. An energy–noise scan shows that energy dominates the multipulse probability, whereas additive noise produces only a modest trend common to all energies, without a noise optimum. The noise-induced formation statistics therefore do not establish canonical
stochastic resonance or escape from a pre-existing
soliton. Coherent control by a weak monochromatic seed extends predominantly single-pulse operation over a noticeably broader energy window, enhancing dissipative-
soliton energy scalability. Within an adiabatic approximation, equal energy sharing among coexisting pulses is stable wherever the single-pulse energy grows less than proportionally with the control energy, as it does over the sampled DSR range. Energy exchange between the pulses then relaxes up to about 200 times more slowly than their total energy.
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All authors Vladimir L. Kalashnikov, Alexander Rudenkov, Evgeni Sorokin, Irina T. Sorokina
Optics
Skyrmion topology of scalar waves in real and momentum space
Nai H. Kwong, Ewan M. Wright, Jan Wingenbach et al. (+4 more)
Generalizations of
magnetic skyrmions to the context of other areas of physics, such as plasmonics, optics (including microcavity polaritons) and even water waves have become an important research topic. However, the generalization of the skyrmion number in such systems is still the subject of active research. While
magnetic skyrmions textures are inherently formed by vectors (
magnetic spin vectors), recent developments in other areas of physics have generalized the concept of skyrmions and skyrmionic patterns to the case in which scalar fields are used to define 3-component pseudo-
spin vectors. This gives rise to a wide variety of skyrmion-like textures, depending on the detailed functional forms of the scalar fields. For example, steady-state outgoing waves in driven-dissipative polariton systems fail to have a well-defined global skyrmion number in real (configuration) space but can have one in momentum space. We classify the skyrmion integral for various scalar fields with different asymptotic behaviors in real space as well as momentum space, and in both cases give conditions for the skyrmion number not to exist, or be integer, half-integer or non-integer. Examples of physical systems to which our analysis can be applied include polariton condensates, water waves and gain-guided
lasers.
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All authors Nai H. Kwong, Ewan M. Wright, Jan Wingenbach, Roman Lebs, Harald Giessen, Stefan Schumacher, Rolf Binder
Optics
Efficient simulation of millimeter-scale complex-modulated integrated Bragg gratings via hierarchical locally periodic eigenmode expansion
Rui Cheng, Jia Meng, Ping Yu et al. (+2 more)
We propose a structure-aware, hierarchical locally periodic eigenmode expansion (HLP-EME) framework for efficiently simulating millimeter-scale integrated Bragg gratings (IBGs) with complex modulation on silicon-on-
insulator platforms. HLP-EME discretizes continuously varying grating parameter profiles into piecewise-constant blocks and exploits the resulting local periodicity of the physical grating structure by reusing the S-
matrix of a representative period within each block. This strategy reduces full-device simulation times for millimeter-scale IBGs to a few minutes, providing a speedup exceeding three orders of magnitude over conventional 3D-FDTD simulations. The method accommodates diverse IBG configurations, including intra-mode gratings, mode-converting multimode gratings and grating-assisted contra-directional couplers. Experimental results validate the predicted reflection spectra of several complex-modulated IBGs and the reflection phase response of one representative design. The framework is further extended to curved waveguides and successfully captures
curvature-induced spectral distortions in millimeter-long, Gaussian-apodized spiral IBGs. Combining full-vectorial modeling with high computational efficiency, HLP-EME provides a powerful tool for designing and optimizing long, complex IBG-based photonic devices.
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All authors Rui Cheng, Jia Meng, Ping Yu, Jihao Wang, Zikun Xie
Optics
Tunable hyperbolic metamaterials for brightening single-photon emission
Manobina Karmakar, Pavel Klok, Filip Ligmajer et al. (+1 more)
Hyperbolic metamaterials (HMMs) are widely used to enhance spontaneous emission through their exceptionally large photonic density of states, yet large Purcell factors (>100) rarely translate into brighter emission, exposing both a practical limitation of HMMs as brightening platforms and a flaw in the Purcell factor itself as a figure of merit. Here we systematically evaluate spontaneous emission enhancement and
photon outcoupling in metal-dielectric HMMs (TiO$_2$/Ag and phase-change Sb$_2$S$_3$/Ag) using effective medium theory, transfer
matrix calculations, and full-wave FDTD simulations. We show that planar HMMs with Purcell factors exceeding 100 have external
quantum efficiencies below 0.01, yielding an actual radiative Purcell factor (PF$_{rad}$) of only 1-2. Nanopatterning the HMM into a photonic
crystal efficiently couples trapped high-k modes into free space, raising PF$_{rad}$ by an order of magnitude. Incorporating the phase-change material Sb$_2$S$_3$ further enables dynamic tuning of the
hyperbolic spectral window and active control over emission brightness: an optimized nanostructured design reaches PF$_{rad}$ ~ 10-15 in the near-infrared, with switching contrast exceeding a factor of 15 upon phase transition. These results establish the radiative Purcell factor as a more reliable figure of merit than the conventional Purcell factor for engineering
quantum emitters, and provide a practical route toward actively tunable, bright single-
photon sources based on
hyperbolic metamaterials.
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All authors Manobina Karmakar, Pavel Klok, Filip Ligmajer, Leonardo de S. Menezes
Optics · Cross-listed from physics.med-ph
Melanin- and linewidth-corrected pulse-oximetry
Giles Blaney, Jodee Frias, Ravi Durbha et al. (+2 more)
Current pulse oximeters tend to overestimate arterial saturation in darkly pigmented patients, increasing occult hypoxemia rates. One proposed mechanism is spectral coloring: melanin contributes to reshaping the detected spectrum of a broad-linewidth source, making the wavelength-dependent parameters behind calibration skin-tone-dependent. Diffuse optics theory allows for a melanin- and linewidth-corrected calibration equation, which to our knowledge has never been tested in vivo. In this work, we fit the empirical linear equation, the diffuse optics theoretical equation, and its corrected form to the public OpenOximetry Repository—considering 98 patients with paired arterial blood-draws, raw photoplethysmograms, and skin reflectance spectra. Accuracy is practically indistinguishable between the three approaches, yet the saturation error's dependence on melanin falls from +2.8 to +1.2 to +0.1 percentage points per unit melanin volume fraction—consistent with the spectral-coloring theory. None of these dependencies on melanin are statistically resolved here—a cohort roughly ten times larger is needed—so the correction is backed by theory and its expected direction. All three calibration approaches carry two degrees of freedom: the theoretical equation drops into existing calibration procedures, and its melanin-aware form needs a per-patient skin-tone measurement. This work demonstrates how the theoretical pulse oximetry model can be applied in calibration.
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All authors Giles Blaney, Jodee Frias, Ravi Durbha, Sergio Fantini, Valencia Koomson
Optics
Angular-Channel Capacity and Nonlocal Wavefront Engineering for Phased-Array–Lens Systems
Mohammad Soltani and George V. Eleftheriades
Wide-angle beam steering with high directivity is fundamentally limited by diffraction, restricting the scan performance of phased-array systems. Here, we establish the bounds governing beam steering with high directivity in phased-array–lens systems and show that nonlocal dielectric metalenses can operate close to these limits. Unlike conventional metalenses that suppress mutual coupling, our approach exploits nonlocal electromagnetic interactions to laterally redistribute energy and expand the spatial width of phase coherence across the aperture. This enables efficient wavefront engineering for uniformly excited planar phased arrays using conventional linear progressive phasing. We further reveal the roles of diffraction and evanescent waves in determining the maximum coherent-aperture expansion and directivity enhancement. The resulting angular-channel bounds identify two distinct operating regimes for passive linear phased-array–lens systems: scan-resolution enhancement and directivity enhancement with preserved scan range. Guided by these limits, we derive geometry-independent design equations and develop an adjoint-based inverse-design framework for passive linear metalenses, enabling planar and cylindrical implementations that operate close to the fundamental limits. We experimentally validate a compact cylindrical metalens that preserves the $50^\circ$ scan range and scan resolution of a phased array with a $3.5\lambda_0$-wide aperture while providing a $2.5$–$3.5\,\mathrm{dB}$ increase in peak directivity. These results establish nonlocal dielectric metalenses as a practical platform for diffraction-limited wavefront engineering in phased arrays.
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Optics
Ultrabroadband Optical Pulses with Quadratic Spectral Phase Part I: Temporal Form
George A. Hine
A time-domain representation for ultrabroadband optical pulses that includes chirp, stretching, and absolute phase is presented. This is accomplished by holomorphic
Fourier transform of a class of spectra that include spectral phase up to second order, resulting in derivatives of the Faddeeva function $w(\zeta)$. Relating the real part of this pulse to physical quantities, its shape is investigated. The derivative order $\eta$ is shown to dictate relative spectral bandwidth. The absolute phase determines the mixing of more localized (Gaussian decay) and less localized (algebraic decay) components of $w(\zeta)$. Second order spectral phase accounts for linear dispersion and is shown to cause a sheering of the Wigner-Ville distribution of the pulse, akin to the linear chirp that would be seen in the quasi-monochromatic case. Along with $\eta$ it determines the pulse length and number of oscillations. A correspondence with the slowly varying envelope approximation is derived for large order $\eta$, although the algebraic decay persists.
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Optics
Inverse design of large-scale freeform meta-optics by breaking the memory wall of full-wave simulation
Hyoseok Park and Yeonsang Park
Gradient-based design of large optical surfaces hits a
memory wall: a stored-history time-domain adjoint needs $24N_t$ bytes per
cell for $N_t$ steps, and every field update is bound by
memory bandwidth. Here we present a validated framework that removes this wall and makes globally optimized freeform meta-optics practical. Its finite-difference time-domain adjoint reconstructs interior fields backwards from two recorded planes, so volume
memory no longer grows with $N_t$, and fused kernels raise
memory-bandwidth use on an H200 GPU from 6.4% to a remarkable 56% of peak. Overlapping tiles, coupled by angular-spectrum propagation and distributed over GPUs, keep tile
memory independent of the aperture. Within hours on one GPU node, we optimize, against one global objective, every density variable of single-layer metasurfaces 100 to 200 $\mu$m across, and design a nine-wavelength lens, a color hologram and a polarization-switched hologram. Confirmed by an independent solver within 1.6%, they substantially outperform meta-atom designs, reaching 1.64, 1.65 and 1.24 times their objectives.
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Optics
Fiber-based scanning levitated nanoparticle force sensor near a metalized membrane
Andrew M. Dana, Samuel J. Borden, Nia Burrell et al. (+10 more)
We describe a fiber-based dual-beam trap for dielectric nanospheres with the ability to transfer the trapped particles into a retro-reflective standing-wave trap within micron-range distances of a metallic mirror surface. We illustrate its capability for three dimensional scanning force sensing over a several square micron area of an ultra-thin gold-coated silicon nitride mirror-membrane with a total thickness of approximately 370~nm. We also demonstrate three-dimensional
laser feedback cooling and zeptonewton force resolution in high-
vacuum at micron range from the membrane, showing promise for future improved tests of
gravity at short distances and other surface force investigations. By using charged nanospheres, we expect the method may be useful for studying fluctuating patch potentials and electric field noise in the vicinity of a surface in the $\sim$ kHz to $\sim 100$ kHz frequency regime.
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All authors Andrew M. Dana, Samuel J. Borden, Nia Burrell, Chethn Galla, Alexey Grinin, Mark Nguyen, Kristina Menon, Shafaq Elahi, Katarina Boskovic Guy, Andrew Laeuger, Evan Weisman, Gambhir Ranjit, Andrew A. Geraci
Optics
Real-Time Event-Based Optical Camera Communication at 80 kbit/s over a 320 m Outdoor Link with 120{\deg} Field-of-View
Francesco Nardo, Peter Krötz, Ricardo Barrios et al. (+1 more)
We demonstrate an event-based optical camera communication system using a 120{\deg} field-of-view sensor. In daylight, three transmitting nodes achieve an aggregate 240 kbit/s, with individual links reaching 106 kbit/s at 1 m and 80 kbit/s at 320 m. Our results, establish a new baseline for event-OCC.
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All authors Francesco Nardo, Peter Krötz, Ricardo Barrios, Sebastian Randel
Optics
Non-Hermitian multimode interferometry
Subhajyoti Bid and Henning Schomerus
Interferometers form a cornerstone of precision measurement, leveraging wave superposition and phase coherence to convert minute physical perturbations into measurable intensity variations. Here, we establish how paradigmatic interferometric architectures, the canonical Michelson and Mach-Zehnder interferometers, can be endowed with entirely new operating principles by replacing conventional beam splitters with judiciously designed non-Hermitian resonators. To uncover how non-Hermitian physics can assist in interferometry, we subject these canonical interferometers to a modern non-Hermitian
symmetry analysis. A fundamentally transformed interference landscape then arises when the resonators and interference pathways collectively induce partially deficient spectral degeneracies, mathematically characterized as multimode versions of exceptional points. Key characteristics of these exceptional interferometers are nonanalytic destructive interference conditions, resulting in distinct bright-fringe and dark-fringe operating regimes organized by non-Hermitian winding and braiding
topology. By revealing how exceptional-point-assisted interference reshapes the canonical geometries, our findings transfer central paradigms of non-Hermitian spectroscopy into the interferometric setting, and establish exceptional-point interferometry as a new platform-independent paradigm for general-purpose precision sensing, applicable from on-chip photonics to macroscopic observatories.
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Optics · Cross-listed from quant-ph
100 million photons per second from a single organic molecule
Siwei Luo, Tim Hebenstreit, Alexey Shkarin et al. (+3 more)
At cryogenic temperatures, organic single-
photon sources (SPSs) offer
Fourier-limited emission, virtually unlimited photostability, and emission wavelengths selectable by molecular design, making them attractive for
quantum metrology, secure communication, and photonic
quantum information processing. However, their efficient integration with photonic microstructures has remained challenging, limiting
photon collection from single organic emitters under cryogenic operation. Here, we demonstrate a cryogenic planar metallo-dielectric
antenna that efficiently directs the emission of a single dibenzoterrylene (DBT) molecule towards the collection optics. The device reaches a collection efficiency of 97% and delivers 100 million
photons per second into the first lens. We measure a
photon indistinguishability for the
Fourier-limited transition of 91.2% while maintaining a high single-
photon purity of 97.7% under strong continuous-wave (CW) and pulsed excitation. These results establish organic molecules as a high-performance platform for single-
photon generation and represent an important step towards scalable organic
quantum photonic technologies.
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All authors Siwei Luo, Tim Hebenstreit, Alexey Shkarin, Jan Renger, Tobias Utikal, Stephan Goetzinger
Optics
Fully passive monolithic silicon quantum photonic circuit for entangled photon-pair generation
David E. Medina, Paul J. Robin, Romain Dalidet et al. (+8 more)
Integrated
quantum photonic
circuits are a key enabling technology for the scalability of
quantum information systems. Among the available platforms, silicon photonics offers an unrivalled capability for the large-scale integration of photonic components within compact footprints. However, the strong index contrast that enables ultra-compact silicon devices also makes them highly sensitive to fabrication imperfections. As
circuit complexity increases, active tuning is generally required to maintain spectral
alignment among the different components, leading to significant power consumption that ultimately limit scalability. Here, we demonstrate a fully integrated silicon
quantum photon-pair source operating without active tuning of any component. The
circuit combines
photon-pair generation in a micro-ring resonator, pump rejection using Bragg filters, and signal/idler demultiplexing through modal add-drop filters with building blocks engineered to minimize sensitivity to fabrication variations. The resulting
circuit achieves excellent experimental
quantum performance. Coincidence rates up to 4000 counts s^-1 with coincidence-to-accidental ratios as high as 100 are obtained across the generated spectrum, while separate two-
photon interference measurements yield raw visibilities exceeding 93% for individually selected ITU wavelength-channel pairs. By eliminating the need for active spectral tuning while maintaining high
quantum performance, this work addresses a major bottleneck in the scaling of complex silicon
quantum photonic
circuits.
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All authors David E. Medina, Paul J. Robin, Romain Dalidet, Sébastien Tanzilli, Anthony Martin, Segolene Olivier, Quentin Wilmart, Laurent Vivien, Laurent Labonte, Carlos Alonso-Ramos, Eric Cassan
Optics
Vertical microcavities with optical Kerr materials
Riya Varghese, Ali Panahpour, Marco Ornigotti et al. (+1 more)
Optical Kerr nonlinearity is central to optical bistability in high-Q microcavities. Here, we show that optical Kerr nonlinearities in Fabry Perot resonators can also result in self-focusing effects, that can substantially modify the Q-factors of the resonators. For the studied cavities, up to five-fold increase in Q-factors is predicted, attributed to reduction of sidewall leakage, confirmed via simulations performed on curved cavities. We also show that for high Q-factor cavities, the higher-order Kerr effect can become relevant already at modest input intensities scaling inversely with Q-factor for a particular n2/n4 ratio. We investigate numerically the role of higher-order Kerr effect on optical bistability responses and find that its inclusion can shift the bistability threshold to higher input intensities than predicted by the standard n2-only model.
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All authors Riya Varghese, Ali Panahpour, Marco Ornigotti, Mikko J Huttunen
Optics
Zero-forward Kerker scattering via synthesized complex-frequency excitation
Jianfei Liu{\dag}, Zheng Gong{\dag}, Ao Li et al. (+3 more)
All objects illuminated with light inevitably cast a shadow – a universal phenomenon encapsulated in the fundamental property that all passive systems with plane-wave illumination feature a non-zero forward scattering amplitude. Since Kerker's landmark 1983 paper, considerable effort has been devoted to overcoming this limitation and achieving the elimination of forward scattering – an objective now widely known as the zero-forward Kerker scattering. However, this objective is fundamentally restricted to active systems, requiring either physical gain in materials or virtual gain in the excitation source. Despite advances in active materials science and non-Hermitian photonics, the experimental realization of zero-forward Kerker scattering still remains an open challenge. Here, we show, both theoretically and experimentally, how zero-forward Kerker scattering can be effectively synthesized by a weighted superposition of readily accessible real-frequency responses. Our synthetic recipe builds on creating an artificial pole at a complex frequency that prevails over inherent scattering poles. These findings not only unlock a realistic experimental framework for non-Hermitian light-matter interactions, but also hold technological relevance for non-invasive sensing and imaging.
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All authors Jianfei Liu{\dag}, Zheng Gong{\dag}, Ao Li, Hongsheng Chen, Stefan Rotter, Xiao Lin
Optics
Observation of symmetry breaking in time-varying scattering systems
Miguel Verde, David Globosits, Thomas F. Allard et al. (+5 more)
From the
Higgs mechanism to
magnetic ordering, spontaneous
symmetry breaking organizes physics across scales. Whether an analogous transition governs waves scattered by periodically driven structures has remained an open experimental challenge. Here we demonstrate a universal
symmetry-breaking transition in a periodically driven finite scattering system. By measuring the multispectral Floquet scattering
matrix of a strongly modulated microwave resonator, we observe a transition from an unbroken
symmetry regime with scattering
eigenvalues of equal modulus to a broken
symmetry regime where their moduli split apart, through an exceptional point. At parametric resonance, this transition culminates in coherent perfect absorption, where a tailored multispectral input state is completely absorbed without outgoing radiation, the singular limit of the underlying transition. Because it arises from the general algebraic structure of the Floquet scattering
matrix rather than from implementation-specific details, this transition should occur broadly in such systems. Unlike instability phenomena in bulk driven media, it emerges in the eigenstructure of a finite scattering operator that couples waves across multiple frequency channels. Our results establish Floquet scattering as an experimentally accessible platform for the observation of
symmetry breaking and for dynamic wave control in driven photonic systems.
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All authors Miguel Verde, David Globosits, Thomas F. Allard, Calvin M. Hooper, Simon A. R. Horsley, Stefan Rotter, Paloma A. Huidobro, Ian R. Hooper
Optics · Cross-listed from nlin.PS
Adiabatic Theory Data on Strongly Chirped Dissipative Solitons of the Cubic-Quintic Nonlinear Ginzburg-Landau Equation
V. L. Kalashnikov, E. Sorokin, A. Rudenkov et al. (+1 more)
This data article provides the
datasets, symbolic derivations, and scripts used to reproduce master diagrams, stationary-phase spectra, windowed first-order coherence functions, and
quantum-noise stability maps for strongly chirped dissipative
solitons of the cubic-quintic complex Ginzburg-Landau equation in normal and anomalous group-delay dispersion regimes. The repository includes node-regularized normal-dispersion spectra and energies; small-parameter expansions of the branch roots; cavity-map gain-loss update relations; Airy uniformization at the normal-dispersion spectral edge; anomalous-dispersion spectra and coherence calculations; and processed tables for plotting and stability analysis. OriginLab projects are accompanied by open-format .csv/.txt numerical tables to support reuse without proprietary plotting software. Data and code repository: https://doi.org/10.5281/zenodo.22690899.
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All authors V. L. Kalashnikov, E. Sorokin, A. Rudenkov, I. T. Sorokina
Optics · Cross-listed from eess.IV
A Unified Frequency-Domain Model for Cascaded Filter-Interpolation Modulation in Tomographic Reconstruction
Detian Li, Yang Zou, Penghao Geng et al. (+1 more)
The fidelity of image reconstruction from projections in linear inverse problems, such as
tomography, is critically dependent on the synergistic interaction between frequency-domain filtering and spatial-domain interpolation. However, a physical model that can quantitatively describe how these two components cascade interact in the frequency domain and ultimately determine image quality is still lacking to this day. Here, we introduce a unified frequency-domain model that conceptualizes the combined effect of filtering and interpolation in the filtered backprojection (FBP)
algorithm as a cascaded modulation process. This model demonstrates that the effective reconstruction spectrum is determined by the original projection data being sequentially modulated by the frequency responses of the filter and the interpolation kernel. Comprehensive numerical simulations and synchrotron radiation CT experiments validate the model, confirming its power to explain the performance hierarchy of classical filter-interpolation pairs under both ideal and noisy conditions. The model successfully predicts key performance characteristics, including spatial resolution and structural fidelity, thereby elucidating the physical principles behind the efficacy of specific combinations. This work establishes a generalizable theoretical foundation for analyzing cascaded systems in linear inverse problems, moving the practice of
algorithm selection in computational imaging from empiricism to a principled, physics-based paradigm.
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All authors Detian Li, Yang Zou, Penghao Geng, Shengkun Yao
Optics
Topology of bound states in the continuum from the angular structure of leading radiation
Nan Zhang and Ya Yan Lu
We show that the angular structure of the leading radiation associated with a bound state in the continuum (BIC) directly encodes
topology, identifies the critical conditions for topological-charge transitions, and reveals the bifurcation of new BIC families under structural variations. For at-$\Gamma$ BICs, rotational and time-reversal
symmetries determine the allowed angular harmonics of the leading radiation and hence the possible topological charges. As an example, we directly identify a BIC with $q=-5$ in a $C_{6v}$ dielectric slab with a triangular
lattice of circular air holes, without computing nearby resonances or tracking the merging of BICs. This BIC is also a super-BIC, exhibiting an ultrahigh quality factor $Q\sim 1/\delta^{10}$ along all directions in momentum space, where $\delta$ is the wavevector detuning parameter. We also use a $C_{4v}$ structure to analyze a topological transition and the associated bifurcation of off-$\Gamma$ BICs. Our results may find applications in resonant, structured, and topological photonics.
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Optics
Breakdown of Axis Separability and Structured Inversion in Finite-Domain Normalized Position Measurements: A Quadrant Photodetector Case Study
Zhiqian Su
Finite-domain normalized spatial measurements combine an incident field,
geometric support, local response, and channel weighting. These operations can break an otherwise separable response, so accurate single-axis calibration alone does not establish separability of a multidimensional measurement. We represent normalized readouts as channel-weight expectations under a parameter-dependent effective measure. For fixed reception and channel operators, local sensitivity is the covariance between the channel weight and the source score. This representation distinguishes axis separability, parameter mixing, and local recoverability, and applies at the appropriate detector level to continuous-electrode position-sensitive detectors, Shack–Hartmann and pyramid wavefront sensors, back-focal-plane split detection, and finite pixel arrays. A quadrant photodetector (QPD) provides an analytically tractable case. Starting from the complete two-dimensional power integrals, we identify the spatial-moment origin of its lowest-order cross term. Axis calibration and system
symmetry then constrain the inverse map, giving Axis-Anchored Cross-Residual Inversion (ACRI). Numerical tests of this QPD realization support the sensitivity relations and show that the constrained cross correction substantially reduces the off-axis bias retained by single-axis inversion. The results illustrate how the general measurement representation guides inverse construction, with performance bounded by the working domain, calibration state, and preserved
symmetries.
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Optics
Global Framework for Dynamics and Criticality of Bound States in the Continuum
Keren Wang, Lujun Huang and Wei Wang
Bound states in the continuum (BICs) exhibit rich momentum-space dynamics, including merging, annihilation, and reconnection across
symmetry directions and bands. Yet these phenomena have largely been explained case by case, without a unified framework to classify or predict them. Here we develop a global
symmetry-equivariant theory for the dynamics of nondegenerate and degenerate BICs. We show that BIC dynamics can be classified into $\alpha$-, $\beta$-, and $\gamma$-processes according to root motion, which not only encompass the reported dynamics in $C_{2v}$, $C_{4v}$, and $C_{6v}$ systems but also include previously unrecognized ones. More importantly, we reveal that distinct dynamics are bridged by the criticality of BICs through a merging of merging, in which selected direction–band branches acquire higher-order radiation zeros. Such a theory predicts which branches become critical and how to tune system parameters to realize them. Following this framework, we construct high-order BICs in full-wave calculations, realizing $Q\sim k^{-10}$ nondegenerate criticality and $Q\sim k^{-8}$ single-branch and band-paired degenerate criticalities. Our framework provides a systematic route to understanding, discovering, and selectively controlling BIC dynamics and high-$Q$ states.
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Optics · Cross-listed from physics.ins-det
Characterization and Active Control of Position-Dependent Timing Dynamics in Superconducting Strip Single-Photon Detectors
Sahil R. Patel, Kristen M. Parzuchowski, Eli Mueller et al. (+6 more)
Superconducting strip single-
photon detectors (SSPDs) have emerged as scalable, wide-strip variants of traditional nanowire counterparts. Despite practical advantages including improved optical fill factors and enhanced signal-to-noise ratios the fundamental detection physics governing these micro-scale geometries remains largely unexplored. Here, we investigate the underlying photoresponse of a 20 um-wide tungsten silicide SSPD, demonstrating a slew-rate-corrected timing jitter of 13.2 ps at 532 nm and 20.5 ps at 1550 nm, alongside saturated internal detection efficiency up to 1550 nm. Using focused free-space optical scanning, we reveal that detector timing jitter is strongly influenced by a spatially dependent slew rate between edge and center absorption events. To mitigate this impact, we utilize a parallel superconducting rail architecture to actively redistribute supercurrent. This in-situ tuning minimizes the latency mismatch and mitigates thermally activated intrinsic dark counts, extending the device's ability to operate at higher temperatures. Finally, comparing these dynamics with time-dependent Ginzburg-Landau (TDGL) modeling elucidates the physical origins of the position-dependent photoresponse, highlighting how superconducting rails or specialized readout electronics can mitigate negative impacts on timing jitter.
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All authors Sahil R. Patel, Kristen M. Parzuchowski, Eli Mueller, Boris Korzh, Emanuel Knehr, Adam N. McCaughan, Martin J. Stevens, Matthew D. Shaw, Jason P. Allmaras