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Saturday 3 October

Optics

Joint Forecasting of Extreme Events through Dual-Stage Cascade Reservoir Computing

Yueyang Wang, Juncheng Huang. Hanxu Zhou and Tao Wang

Reservoir computing (RC) offers an efficient data-driven approach for forecasting extreme events (EEs), which correspond to rare and large-amplitude dynamical occurrences. We propose a dual-stage cascade framework that jointly predicts both the timing and peak intensity of upcoming EEs. A traditional RC branch integrates long-term precursor dynamics to support stable detection and long-horizon prediction, while an NGRC branch captures local nonlinear waveform geometry to improve fine-grained time-to-peak localization and complement peak-intensity estimation. The fused features then feed a ridge classifier that issues a binary alarm upon detecting precursors. Only then do two ridge regressors, trained on true-positive snapshots, estimate time-to-peak and peak intensity. This classify-then-regress design addresses severe class imbalance without data resampling. Evaluated on simulated pump-modulated VCSEL data, the hybrid model achieves a SEDI value >0.8, with MAEs around 0.2 ns and 0.2 a. u., maintaining performance up to a 20 ns warning horizon. The framework advances extreme-event forecasting from binary warnings to fully quantitative dual-objective prediction.
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Optics · Cross-listed from physics.atom-ph

Origin of the inhomogeneous linewidth in a solid state $^{229}$Th:CaF$_2$ nuclear clock

Kai Li, Tian Ooi, Jack F. Doyle et al. (+7 more)

Narrow linewidth (high-Q) quantum discriminators are essential for realizing solid-state $^{229}$Th nuclear clocks, yet the observed transition linewidths remain at the tens-to-hundreds-of-kilohertz level, far exceeding the sub-Hertz linewidth set by the radiative lifetime of the nuclear isomer. Here, we investigate the origin of this broadening in $^{229}$Th:CaF$_2$ through systematic measurements of the linewidth as functions of temperature, thorium concentration, and quadrupole state, accompanied by theoretical analysis and first-principle simulations. We find that the linewidth is independent of temperature, increases linearly with thorium concentration, and depends strongly on the quadrupole state. Data analysis identifies variations of the local electric-field gradient (EFG) as the dominant source of inhomogeneous broadening and reveals that the EFG disorder increases linearly with thorium concentration. The observed Lorentzian line shapes and linewidth linear concentration dependence are explained naturally from the $1/r^3$ scaling of a random distribution of long-range dopant-induced perturbations. Complementary atomistic and ab initio density-functional-theory calculations reproduce these characteristic features and provide insights into the microscopic defect configurations responsible for the broadening. These results establish the dominant broadening mechanism in solid-state $^{229}$Th and provide guidance for engineering nuclear-clock materials with reduced inhomogeneous broadening.
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All authors Kai Li, Tian Ooi, Jack F. Doyle, Konstantin Herb, Emil Pellett, Martin Pimon, Thorsten Schumm, Steven M. Girvin, Leo Radzihovsky, Jun Ye

Friday 2 October

Optics · Cross-listed from quant-ph

Modal input-output theory for quantum nanophotonics from the first-order Maxwell operator

Ankit Kundu, Ishita Agarwal, Adhyyan S. Mansukhani et al. (+1 more)

We develop a quantum input-output theory for open photonic systems based on macroscopic quantum electrodynamics using the first-order electromagnetic Green's function. Quantum fields enter and leave the photonic system through waveguide ports, while the electromagnetic Green's function propagates the fields through the arbitrary interior of the photonic system, which may be dispersive and absorbing. The resulting relation contains a port-to-port scattering matrix and a Langevin-noise contribution from material absorption that together preserve the bosonic output commutation relations. For embedded emitters, the low-saturation and single-excitation scattering response is determined by Green's functions connecting the ports and emitters while retaining the non-Markovianity of the photonic environment. Using finite-difference time-domain simulation, we calculate the emitter-modified transmission for a nanophotonic cavity and inverse-designed coupler, providing a direct route from computed electromagnetic response to a quantum input-output model.
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All authors Ankit Kundu, Ishita Agarwal, Adhyyan S. Mansukhani, Jonathan D. Hood

Optics · Cross-listed from hep-th

Comment on ”Chiral electromagnetic surface waves on Chern-Simons interfaces” Phys.Rev.D114(2026)L051903 and on arXiv:2606.12513 by N. Kaloper

Igor Bandos and Bohdan Zvorskyi

We demonstrate that Maxwell electrodynamics interacting with a planar Chern-Simons interface does not have plane wave solutions localized on the interface. We re-examine the derivation of such waves presented by N. Kaloper in [Phys.Rev.D114(2026)L051903] and show that at an intermediate step certain terms were missed in an equation therein. Taking these terms into account changes the final conclusion of [Phys.Rev.D114(2026)L051903]. We also show that the method used in [arXiv:2606.12513 [hep-th]] to reproduce the same result is not consistent.
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Optics

Beyond the PT-Broken Phase: Constant-Frequency Oscillation from Floquet Hybridization

Xiaoke Gao, Xiaoyin Sha, Xunyan Sun et al. (+3 more)

Constant-frequency oscillation is usually tied to the broken phase of a spatially coupled PT-symmetric dimer, where the eigenfrequencies form a complex-conjugate pair with a fixed real part. This work shows that an analogous locking can instead come from Floquet hybridization in a synthetic frequency dimension. Periodic gain–loss modulation folds the spectrum into replicas spaced by the drive frequency $\Omega$. Coupling between neighboring replicas opens an additional real-part degeneracy at the edge of the Floquet Brillouin zone. The hybridized Floquet mode at $\omega_0\pm\Omega/2$ requires the minimum gain and is therefore selected for the self-oscillation. A Floquet PT-symmetric circuit with a JFET time-varying negative resistance confirms the prediction. The observed constant-frequency oscillation contains two frequency components of comparable amplitude, separated by the modulation frequency, which identifies its origin from Floquet hybridization rather than ordinary PT-symmetry breaking or dispersion flattening. More broadly, once a suitably symmetry-constrained spectral degeneracy is established, self-sustained frequency pinning can arise beyond the conventional spatial PT-broken phase.
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All authors Xiaoke Gao, Xiaoyin Sha, Xunyan Sun, Xianglin Hao, Huaiqing Zhang, Tianyu Dong

Optics

Quantitative spin-orbit engineering enables subwavelength-scale programmable polarization states for versatile photonic functionalities

Shuaijie Yuan, Xuefeng Zhang, Jin Yang et al. (+7 more)

Precise and programmable control of optical polarization provides a versatile vectorial degree of freedom for light-matter interaction and optical information encoding. Existing polarization state generators (PSGs), however, suffer from poor switchability and modest fidelity at the micrometer scale, which severely constrains their practical applicability. To overcome these limitations, here we present a quantitative spin-orbit engineering that enables the dynamic synthesis of arbitrary polarization states at subwavelength dimensions. The core concept is to tailor conjugate optical vortices that independently address the orthogonal spin components of a vectorially polarized light. This spatial modulation scheme annihilates intrinsic topological charges and reshapes the spin-orbit interaction, thereby coherently constructing polarization ellipses on demand. Leveraging this mechanism, we experimentally synthesize diffraction-limited arbitrarily polarized beams spanning the entire Poincare sphere with fidelity over 99%. As proof-of-principle demonstrations, we apply the miniaturized PSG platform to Mueller-matrix polarization microscopy, pixel-level polarization encryption, and parallel polarization-information encoding, illustrating its broad utility of programmable polarization control for subwavelength polarimetric imaging and reconfigurable multiplexed polarization encoding. Compared with state-of-the-art PSGs, our approach uniquely integrates rapid programmability, high fidelity, and subwavelength localization in a single architecture. These multifunctional capabilities of this work position the platform as a promising route for advancing Mueller matrix polarization microscopy, multidimensional optical storage, and secure optical information processing, and beyond.
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All authors Shuaijie Yuan, Xuefeng Zhang, Jin Yang, Min Cheng, Xinyu Ma, Jinhai Zou, Jinyong Leng, Zhongquan Nie, Bing Lei, Pu Zhou

Optics · Cross-listed from quant-ph

Mode-tunable inter-core coupling of photon-number-resolved quantum light in a telecom multicore fiber

Chiran Wijesundara, Yasmin Sarhan, Henry Strong et al. (+3 more)

Multicore optical fibers (MCFs), developed to scale classical telecommunications, are gaining traction as a quantum platform for high-dimensional key distribution, entanglement, and photonic quantum walks. So far, quantum light has occupied these fibers only as single-mode path channels; the spatial-mode structure within each core has remained untouched. Here we operate a telecom-grade 39-core fiber far from its design wavelength, where each core supports exactly two LP mode groups (LP01, LP11), and measure heralded photon-number states |1> and |2>, resolving the photon number simultaneously with the intra-core spatial mode or with the core index. Displacing the launch prepares a coherent LP01-LP11 superposition whose single-sided intensity pattern shows that the intermodal phase is preserved over the fiber: a drift-resolved joint fit gives a pixel asymmetry (0.4% vs 47%) incompatible with an incoherent mode mixture. Because the two modes couple to neighboring cores at different rates (kappa_LP11/kappa_LP01 = 2.4), the launched mode content acts as a state-selectable coupling knob: the effective inter-core coupling of the passive fiber is set by the launch alone (3.9-13.1%), a tunability that otherwise requires electro-optic, thermo-optic, or mechanical reconfiguration. The propagation is photon-number independent: the per-photon crosstalk of heralded |2> states equals that of |1>, bounding any Fock-state dependence to |dx/x| < 6.1% (95% CL), and the imaged mode distributions of |1> and |2> agree to better than 1%. This measured linear-optics null, validated against exact Fock-space simulation, is the baseline against which genuine multiphoton interference in fiber quantum walks must be certified; we also show how coincidence-based event selection produces spurious photon-number-dependent crosstalk if accidentals are not subtracted.
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All authors Chiran Wijesundara, Yasmin Sarhan, Henry Strong, Jeffrey Cai, Dan T. Nguyen, Tim Thomay

Optics · Cross-listed from astro-ph.IM

Design, Fabrication, and Free-Space Characterization of a Two-Photon-Polymerized Nano-printed Photonic Lantern

Kyra Watts, Natasha Popenoe, Benjamin Gerard et al. (+6 more)

Photonic lanterns provide an interface between multimode optical fields and arrays of single-mode waveguides, making them promising components for modal filtering, wavefront sensing, and high-contrast astronomical instrumentation. We present the design, simulation, two-photon-polymerization fabrication, and free-space characterization of a compact photonic lantern optimized for operation at $ 1050~\mathrm{nm} $. The device was designed to transform a multimode input into five nominally single-mode output waveguides. Eigenmode-expansion simulations in Ansys Lumerical MODE were used to optimize the lantern geometry while minimizing insertion loss and output-channel power nonuniformity. The optimized structure was fabricated using a Nanoscribe Photonic Professional GT2 two-photon-polymerization system and developed as a standalone polymer-waveguide component. The fabricated lantern was characterized using a free-space optical setup consisting of a $ 635~\mathrm{nm} $ laser for preliminary characterization, collimation and focusing optics, and camera-based imaging of the transmitted fields. Measurements were used to assess optical throughput, output intensity distribution, and light-guiding performance. Differences between simulated and measured results may arise from the wavelength mismatch, fabrication tolerances, material and surface-scattering losses, alignment errors, and deviations from the idealized material and geometric parameters used in simulation. These results demonstrate a compact, additively manufactured photonic-lantern platform and establish a pathway toward free-space-coupled astrophotonic systems for future high-contrast exoplanet-imaging instrumentation.
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All authors Kyra Watts, Natasha Popenoe, Benjamin Gerard, Paul Pax, Dominic Sanchez, David Feng, C. Cole Dunn, Cari Johnston, Xiaoxing Xia

Optics

Active Phase and Amplitude Modulation in Perovskite Polaritonic Waveguides

Andrea Zacheo, Marco Marangi, Tim Colin Meiler et al. (+6 more)

Integrated photonic technologies require active materials capable of providing large optical modulation within compact footprints and low losses. The large optical nonlinearities of exciton-polaritons offer a promising route to meet these requirements, yet their integration into photonic circuits remains challenging because strong light-matter interactions must be combined with low-loss transport and spatially localized control. Here, we demonstrate active phase and amplitude modulation in halide perovskite polaritonic waveguides integrated with electrical microheaters. Local electrothermal actuation drives a structural phase transition in the perovskite, modifying the complex refractive index dispersion near the excitonic resonance. By tuning the excitonic fraction of the propagating mode, the waveguides can therefore operate either as a phase shifter with a tuning efficiency of 0.2 mW mm, approximately one order of magnitude lower than silicon modulators with similar geometries, or as an intensity switch , providing 1 dB/um modulation depth at 20 mW. Our work establishes phase-change excitonic reconfiguration as a route towards compact polariton circuits for nonlinear photonic applications.
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All authors Andrea Zacheo, Marco Marangi, Tim Colin Meiler, Filippo Martinelli, Antonio Fieramosca, Vincenzo Ardizzone, Giorgio Adamo, Daniele Sanvitto, Cesare Soci

Optics

Two-Laser Heterodyne Detection System for ALPS II

Henry Frädrich, Aaron D. Spector, Axel Lindner et al. (+1 more)

The Any Light Particle Search II employs a highly sensitive heterodyne detection system to measure an ultra-weak electromagnetic field that is reconverted from axions inside a regeneration cavity (RC). The initial design of the heterodyne system utilized a local oscillator laser (LO) that was resonant with the RC to form an interference beatnote with the weak signal field exiting the cavity. A weakness of this design is that it is possible for the out-of-mode field component of the LO to be larger than the in-mode component, allowing its noise to dominate the optical component of the noise budget and reducing the SNR of the experiment. This problem can be addressed by introducing a second, non-resonant laser as the LO. Since the in-mode light of this laser does not couple to the cavity, significantly more of its power is reflected than when the LO is resonant. We present a model for the measurement noise that predicts these design changes increase the SNR by a factor of roughly 35. This model was then confirmed experimentally by injecting a weak signal to the RC and examining the difference in the sensitivity of the detection system in each of these configurations.
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All authors Henry Frädrich, Aaron D. Spector, Axel Lindner, Guido Müller

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

Second-order Raman and anharmonic lattice dynamics in lead-halide perovskites

Chao Shen, Florian Kluibenschedl, Ayan A. Zhumekenov et al. (+4 more)

We explore the microscopic origin of THz-driven lattice dynamics in methylammonium lead bromide CH$_3$NH$_3$PbBr$_3$ using two-dimensional THz Kerr-effect spectroscopy. The analysis of the experiment enables discrimination between competing nonlinear excitation mechanisms and reveals that the dominant pathway is phonon-mediated rather than purely photonic. In particular, we argue that the commonly observed 1.15~THz Raman-active $A_g$ mode is not excited directly by the THz electric field. Instead, it emerges through cubic anharmonic coupling to an infrared-active phonon at 0.68~THz. Furthermore, a satellite feature at 1.36~THz is identified as a two-phonon Raman response of the same infrared-active mode. The observation of strong quadratic coupling involving the infrared-active phonon suggests an unconventional form of electron-phonon dressing present in lead-halide perovskites.
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All authors Chao Shen, Florian Kluibenschedl, Ayan A. Zhumekenov, Mikhail Lemeshko, Osman M. Bakr, Artem G. Volosniev, Zhanybek Alpichshev

Optics · Cross-listed from quant-ph

Pathway-resolved analysis of internal conversion enabled by Gaussian boson sampling

Mikhail Roiz, Rashid Valiev, Jan-Lucas Eickmann et al. (+4 more)

Gaussian Boson Sampling (GBS) has provided strong evidence of quantum advantage, motivating the search for real-world applications. Such applications rely on mapping physical problems to the native GBS output: photon-number patterns sampled from a highly non-trivial probability distribution. Here we derive a GBS-compatible mapping for the rate constant $k_\mathrm{IC}$ of internal conversion (IC), incorporating two important physical effects – Duschinsky rotations and Herzberg–Teller contribution. We validate this framework using sampling simulations of dibenzoterrylene, reproducing reported values of $k_\mathrm{IC}$. Beyond $k_\mathrm{IC}$ reconstruction, we show that the photon-number patterns of GBS encode the vibrational mode combinations responsible for the IC process, which we refer to as non-radiative pathways. This pathway-resolved data can then be grouped in different ways to extract multiple physically motivated observables. In particular, it enables $k_\mathrm{IC}$ analysis at several levels, from individual modes and mode family contributions to recurring vibrational configurations shared by multiple pathways. We find that Duschinsky rotations increase the fraction of $k_\mathrm{IC}$ associated with correlated vibrational pathways from 46% to 86%, and identify the mode combinations with the largest rate contributions. These pathway-resolved insights can guide targeted molecular modifications, including selective deuteration and bond substitution, to control non-radiative decay.
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All authors Mikhail Roiz, Rashid Valiev, Jan-Lucas Eickmann, Theo Kurten, Benjamin Brecht, Michael Stefszky, Christine Silberhorn

Optics · Cross-listed from quant-ph

Stimulated Parametric Down-Conversion: From Foundational Coherence to Structured Light Applications

M. F. Z. Arruda, M. G. Damaceno, G. H. dos Santos et al. (+4 more)

Stimulated parametric down-conversion (StimPDC) is the seeded version of the process that underlies much of photonic quantum information. Replacing the vacuum at one input port with a coherent seed leaves the interaction Hamiltonian, the phase-matching function and the two-photon amplitude unchanged, while raising the output to levels accessible with ordinary classical detectors. This review treats the transverse spatial physics of that process. We show that a single relation, in which the idler amplitude is the pointwise product of the pump field with the complex conjugate of the seed, organizes results usually presented separately: the image and coherence transfer experiments of the 1990s; phase conjugation and its use for wavefront correction; the conservation and conjugation of orbital angular momentum, together with the generation of radial modes and geometric intensity patterns; and the processing of vector vortex beams carrying spatially varying polarization. We then consider StimPDC as an instrument rather than as an object of study, covering stimulated emission tomography, the experimental realization of Klyshko's advanced-wave picture, and the transfer of partial coherence, including the conservation of the twist phase of twisted Gaussian Schell-model beams. We close with the quantum regime, reached when the seed approaches the single-photon level or the idler is used as a herald, and with an assessment of open problems and prospective applications.
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All authors M. F. Z. Arruda, M. G. Damaceno, G. H. dos Santos, R. Medeiros de Araújo, N. Rubiano da Silva, S. P. Walborn, P. H. Souto Ribeiro

Optics · Cross-listed from quant-ph

Self-organized Layered Structures of Nitrogen-Vacancy Centers with Preferential Orientation in Heteroepitaxial Diamond Films

Vadim Lebedev, Alejandro Martínez-Méndez, Jesús Moreno-Meseguer et al. (+6 more)

Here, we report the fabrication and characterization of single crystal diamond films on a two-inch wafer-scale containing three-dimensional layered structures of negatively charged nitrogen-vacancy color centers (NV$^{-}$). The (100)-oriented layered diamond films were grown by chemical vapor deposition (CVD) to create spatially separated regions of enhanced emission associated with NV$^{-}$ centers. Such localized emission enhancement as well as 2D and 3D arrays of spins could enable close-packed architectures for emerging quantum devices, such as data processors, memory cells, and magnetic sensors. A cyclic sequence of CVD growth and oxygen-plasma etching is employed, resulting in the in-situ formation of layered inverted pyramidal structures with flat $\{$111$\}$ sidewalls. These pits are subsequently overgrown by nitrogen-doped diamond to achieve NV$^{-}$-rich facets with a uniform N-V bond arrangement and improved nitrogen incorporation efficiency.
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All authors Vadim Lebedev, Alejandro Martínez-Méndez, Jesús Moreno-Meseguer, Jan Engels, Jürgen Weippert, Jan Kustermann, Felix Hoffmann, Javier Prior, Jan Jeske

Optics

Metasurface-on-Lithium-Niobate Architecture for Spin-decoupled Second Harmonic Wavefront Shaping

Yiwen Liu, Chao Meng, Sergey I. Bozhevolnyi et al. (+1 more)

Nonlinear metasurfaces (NMSs) enable simultaneous generation and manipulation of harmonic light with ultrathin nanophotonic platforms. However, conventional NMSs typically adopt a monolithic single-layer configuration in which frequency conversion, polarization selection and wavefront engineering are intertwined to simultaneously occur within the same nonlinear meta-atoms, making these functionalities intrinsically interdependent and imposing constraints on material choice, structural symmetry, and the available geometric parameter space. Here, we propose and experimentally demonstrate a metasurface-on-lithium-niobate architecture that physically separates harmonic light generation and wavefront manipulation. In this platform, a z-cut thin-film LN layer serves as a spin-selective second-harmonic source through its intrinsic bulk second-order nonlinearity, while an overlaid dielectric metasurface subsequently and independently molds wavefronts of generated harmonic fields. The two-step process, by virtue of harmonic generation being decoupled from wavefront shaping, removes symmetry constraints associated with conventional nonlinear meta-atoms and enables the direct transfer of well-established linear metasurface design strategies to harmonic wavefront engineering. As proof-of-concept demonstrations, we realize spin-decoupled second-harmonic beam steering and spin-multiplexed holography, achieving high-contrast routing of harmonic signals with orthogonal spin states into distinct diffraction channels and high-fidelity reconstruction of independent holographic images. By redirecting the harmonic wavefront control from the meta-atom engineering to the modular system-level design, our approach establishes a versatile route toward integrated nonlinear meta-optics and provides a scalable platform for advanced optical functionalities.
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All authors Yiwen Liu, Chao Meng, Sergey I. Bozhevolnyi, Fei Ding

Optics

Nonreciprocal Coupling Induced Non-Hermitian Entanglement in Optomechanical Systems

W. Y. Hu, H. Yi, H. N. Liu et al. (+4 more)

Quantum entanglement, one of the most intrinsic properties of quantum mechanics, corresponds to a key resource for quantum information. Exceptional points (EPs) are special phase transition points in non-Hermitian systems. Nonreciprocity achieves one-way motion by breaking reciprocal symmetries. However, the connections among quantum entanglement, EPs, and nonreciprocity remain unexplored in non-Hermitian systems. In this paper, we investigate the manipulation of optomechanical entanglement by non-Hermitian coupling between two counter-propagating optical modes based on a whispering-gallery-mode (WGM) resonator coupled with two Rayleigh scatterers. EPs can periodically appear by controlling the relative angle between two nanoparticles. Moreover, the spinning resonator can induce opposite frequency shifts in two counter-propagating optical modes. The logarithmic negativity of entanglement reaches the maximum at EPs, leading to significant enhancement of optomechanical entanglement. In contrast, the entanglement is suppressed at non-EPs but can be recovered by the Sagnac-Fizeau shift. Specially, by driving the resonator at EPs while spinning it at the optimal rotation speed, we achieve switching between classical and quantum nonreciprocity.
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All authors W. Y. Hu, H. Yi, H. N. Liu, S. Y. Ge, Cheng Shang, Yan-Hui Zhou, H. Z. Shen

Optics

A Theory of Nested Cascading in Directed Logic

Ihar Babushkin, Oliver Melchert, Ayhan Demircan et al. (+1 more)

In directed logic (DL), electronically controlled optical elements serve as photonic gates. Such electro-optical elements are of mixed nature: they have two inputs–electronic and optical–but only one, optical, output. This makes cascading such gates without repeated conversion between optical and electronic representations cumbersome. This problem can be largely overcome using the nested cascading scheme proposed by Shamir and Hardy [Opt. Express, 17, 150 (2007)]. Although promising as a solution to the cascading problem, the Shamir-Hardy scheme has so far been proved or implemented only for a few simplest cases. Here, we develop a general rigorous theory of nested cascading, valid for an arbitrary number of gates. We propose a variant of the algorithm which easily extendable to large number of gates, and rigorously prove its validity. Furthermore, we analyze how nested cascading scales with the size of the corresponding Boolean formula. We show that good (linear) scalability is guaranteed in many important cases, while the average scaling with respect to the corresponding Boolean formulas is only moderately polynomial, with an exponent of approximately 3/2. Yet, the worst-case scaling remains exponential with respect to more general Boolean circuits allowing sharing and reuse of intermediate results.
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All authors Ihar Babushkin, Oliver Melchert, Ayhan Demircan, Uwe Morgner

Optics

Non-Markovian Entanglement via Parametrically Mediated Molecular Cavity Optomechanics

Wenyao Hu, H. N. Liu, X. C. Zhang et al. (+3 more)

Quantum entanglement in molecular cavity optomechanical (COM) systems serves as a fundamental resource to explore quantum-enhanced sensing, coherent molecular dynamics, and quantum information processing, which has been studied under Markovian approximation but not yet explored in non-Markovian reservoirs. In this paper, we propose a scheme to manipulate quantum entanglement in molecular COM system coupling with degenerate optical parametric amplifier (DOPA) under Markovian approximation. We reveal that both strength and phase of DOPA can be tuned to enhance optical-vibration entanglement and suppress vibration-vibration entanglement. The optical-vibration entanglement can exist at room temperature, demonstrating strong robustness against thermal noise. Moreover, we extend results from Markovian to non-Markovian regimes, which can further enhance both types of entanglement with DOPA fixed. In particular, we find that non-Markovian effects can reverse influences of DOPA on vibration-vibration entanglement from suppression to enhancement, leading to regeneration of entanglement. The scheme provides an effective way to control and enhance quantum entanglement in molecular COM system through steering DOPA and non-Markovian effects.
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All authors Wenyao Hu, H. N. Liu, X. C. Zhang, Cheng Shang, Yan-Hui Zhou, H. Z. Shen

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

Topological insulators on complex networks

Sunkyu Yu, Xianji Piao and Namkyoo Park

The landscape of topological insulators has expanded beyond its traditional domain of periodic lattices with short-range hopping. Related studies have explored topological phenomena under non-Euclidean geometries, disordered structures, and long-range hopping, progressively narrowing the gap between topological phases of matter and complex networks. Here we demonstrate that genuine complex networks, far beyond periodic lattices and their conventional variants, can themselves host topological insulating phases. By developing a nonconflicting design framework for multiple topological objectives, we realize topological insulators in high-degree Hofstadter lattices and across regular, small-world, and random networks. This generalization uncovers distinct network-specific features, including an expanded range of attainable topological characteristics, a degree-dependent transition from Hofstadter-type to Haldane-type Chern insulators, and, most notably, the superior robustness and reconfigurability of small-world topological insulators. Our graph-theoretic framework establishes network complexity as a resource for realizing high-capacity and reconfigurable topological insulators.
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Optics

Fast Nanophotonic Inverse Design using Precomputed Numerical Green Functions

Thi Phuong Thao Nguyen, James Wang and Constantine Sideris

Inverse design has been transformative in nanophotonics, providing an automated means of realizing high-performance, non-intuitive devices. However, the primary bottleneck of existing inverse design approaches is their reliance on time-consuming and computationally expensive full-wave electromagnetic simulations. In this work, we extend the Precomputed Numerical Green Function (PNGF) method for the first time to nanophotonic inverse design, accelerating evaluation of the forward problem by multiple orders of magnitude with no loss in accuracy compared to the full-wave solution. After a single, fully parallelizable precomputation step, both the objective function and its gradient can be evaluated through simple calculations whose cost scales linearly with the size of the design region. A low-rank matrix update technique further reduces the cost of objective function evaluation, yielding sub-millisecond computation times per iteration. Design examples using both gradient-based level-set optimization and tile-flipping direct binary search often achieve more than three orders of magnitude speedup in design time, resulting in an ultrafast photonic inverse design platform that can design new devices from scratch in seconds.
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Optics

Absence of universal backscattering immunity in reciprocal photonic waveguides

Yecheng Hu, Ming Gao, Wei Xie et al. (+6 more)

Suppressing parasitic back-reflection caused by imperfections, such as random defects, material inhomogeneities, localized inclusions, and fabrication-induced geometric deviations, has long been a central objective in optical-waveguide engineering. In this Letter, we theoretically establish that universal immunity to backscattering from arbitrary disorder is fundamentally impossible in reciprocal optical waveguides, irrespective of whether the underlying structure is topologically trivial or nontrivial.We establish this result through two complementary constructions of physically admissible reciprocal perturbations. The first considers weak permittivity perturbations of finite spatial extent within the first Born approximation, whereas the second considers optically small dielectric perturbations of finite contrast. In each construction, an admissible realization exists that produces a nonzero leading-order backward-scattering amplitude. We trace the fundamental origin of this limitation to the absence in photons of the intrinsic spin-$\tfrac{1}{2}$ and fermionic time-reversal structure underlying Kramers protection in electronic systems. Consequently, any mechanism that enforces photonic backscattering suppression throughout a prescribed class of disorder must instead be engineered into the underlying electromagnetic structure and its constitutive response, which can itself be modified by generic reciprocal perturbations. Numerical examples in representative reciprocal topological waveguides further illustrate these limitations for random defects and sharp bends. We further identify several constructive strategies for suppressing back-reflection within certain prescribed classes of disorder.
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All authors Yecheng Hu, Ming Gao, Wei Xie, Yinxiang Xiong, Canqiu Dong, Zhuoyuan Lu, Yuerui Lu, Sid Assawaworrarit, Alex Y. Song

Thursday 1 October

Optics

Digital twin for full field-of-view Fraunhofer holographic patterning

Antoni J. Wojcik, Dilawer Singh, Hannah J. Joyce et al. (+1 more)

Computer-generated holography allows for nearly complete dynamic control of optical fields, but discrepancies between idealised propagation models and physical hardware limit its performance, particularly across large fields of view. We present a compact differentiable model of a Fraunhofer holographic projector which describes the complete propagation chain, from a phase-only spatial light modulator (SLM) to the camera recording the focal plane of a Fourier lens. It uses physically interpretable parameters for the SLM, illumination, pupil, coherent stray light, and camera. The model is identified in situ from noise-probed hologram-image pairs without additional hardware, system modification, or camera-in-the-loop refinement. The recovered digital twin is used to generate holograms for patterns spanning the entire first diffraction order of the SLM at its spatial-bandwidth limit. This full-field capability is enabled by measuring field-dependent pupil aberrations and compensating severe inter-pixel crosstalk by operating at the $4\pi$ phase modulation range. The stray light responsible for residual zeroth-order artefacts is recovered in amplitude and phase, allowing its physical origin to be investigated, and its contribution suppressed during hologram synthesis. The work establishes a framework for calibration-aware field synthesis in holographic systems operating in the Fraunhofer regime for applications such as maskless lithography and optical tweezer arrays.
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All authors Antoni J. Wojcik, Dilawer Singh, Hannah J. Joyce, Timothy D. Wilkinson

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

Quantum materials QED with van der Waals crystals

Suheng Xu, Brian Vermilyea, Ran Jing et al. (+19 more)

A central goal of the emerging field of materials QED is to harness subwavelength electromagnetic confinement in engineered cavities to tailor light-matter interactions. Here, we demonstrate that van der Waals multilayer cavities composed of stacked graphene and hexagonal boron nitride (hBN) provide unprecedented control over hybridization between their electromagnetic resonances. By magnetically tuning graphene inter-Landau-level transitions (ILTs) into resonance with hBN phonons, we witness broadband, mode-selective strong coupling in the mid-infrared. Our quantum-material QED framework shows that cavity geometry and layer placement jointly control both coupling strength and modal selectivity. For experimentally realistic cavity parameters, the predicted mode splitting exceeds the width of the hBN Reststrahlen band, providing a direct route to the ultrastrong coupling regime. Together, these results establish van der Waals multilayer cavities as a scalable platform for tunable multimode QED and broaden the design space for reconfigurable quantum materials.
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All authors Suheng Xu, Brian Vermilyea, Ran Jing, Lukas Wehmeier, Jihoon Park, Rafael A. Mayer, Xinzhong Chen, Samuel L. Moore, Fuyang Tay, Boyi Zhou, Wenjun Zheng, Dihao Sun, Birui Yang, Cory R. Dean, Daniel Cazorla, Xu Du, Milan Delor, Andrew J. Millis, Angel Rubio, Michael M. Fogler, Mengkun Liu, D. N. Basov

Optics

Intrinsic electromagnetic properties

Eduardo Barredo-Alamilla, Timur Z. Seidov, Daniel A. Bobylev et al. (+1 more)

Electromagnetic properties of materials are commonly inferred from how they scatter light. Here we show that this diagnostic is fundamentally incomplete. We predict the existence of an intrinsic electromagnetic property that remains invisible in any scattering experiment independently of geometry, polarization, far-field or near-field excitation. Still, this property affects the radiation emitted by the sources embedded inside the material. We reveal this phenomenon for a specially designed nonreciprocal magnetoelectric material combining axion and dual axion responses. Our results establish intrinsic electromagnetic properties as a distinct class of material responses and show that scattering experiments alone are insufficient to characterize matter.
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All authors Eduardo Barredo-Alamilla, Timur Z. Seidov, Daniel A. Bobylev, Maxim A. Gorlach

Optics

Thin-capping layer epitaxial quantum dots for near-field quantum photonics

Yuting Guo, Jonathan Bar-David, Pasquale Cilibrizzi et al. (+3 more)

Epitaxial quantum dots (QDs) are widely recognised as one of the best quantum light sources, given their good stability, brightness, quantum efficiency and coherence. To reach such properties, QDs are protected from potentially detrimental surface states by a relatively thick capping layer, typically exceeding 50nm. This prevents the implementation of near-field effects, like plasmonic-based ones, that can dramatically increase the light-matter interaction, since the control of the spontaneous emission dynamics and directionality of the emission can only occur if the emitter is in close proximity (typically tens of nanometers or less) from the metallic structures. In this work, we report the growth and optical characterisation of InAs/GaAs QDs with GaAs capping layer thickness of 10nm, 20nm, and a more standard 95nm. Remarkably, we observe emission linewidths up to 5 times smaller than previously reported, with unperturbed excitonic lifetimes. These results demonstrate that the epitaxial QD's high optical quality can be maintained even when the emitters are at reduced distances from the surface, opening the path for the exploration of near-field light-matter interactions with coherent and stable emitters, suitable for quantum technology applications.
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All authors Yuting Guo, Jonathan Bar-David, Pasquale Cilibrizzi, Sung-Yul L. Park, Jin Dong Song, Luca Sapienza

Optics

Programmable nonlinearity within nanophotonic waveguides

Benjamin A. Ash, Ryotatsu Yanagimoto, Mandar M. Sohoni et al. (+8 more)

Nonlinear nanophotonics enables the engineering of optical functions using light-matter interactions in nanoscale structures with carefully designed geometries. Phase matching in nonlinear optics is typically essential for realizing high efficiency for desired processes and engineering of sophisticated functions, but it can be challenging to reliably achieve in nanophotonic waveguides. Conventionally, phase matching in nanophotonics is achieved through nanofabrication, e.g., by poling a device's nonlinear material using electrodes with fixed geometry. This approach has two drawbacks: the optical functions a device can perform are fixed at the time of fabrication, and the device's performance can be degraded by fabrication imperfections. Here, we circumvent these limitations by engineering programmable $\chi^{(2)}$ holograms inside nanophotonic waveguides, enabling reconfigurable quasi-phase matching that can be updated after device fabrication in approximately one second. By projecting structured optical illumination onto photoconductive electrodes, we generated spatial patterns of electric-field-induced $\chi^{(2)}$ to exert spectral, modal, and polarization control over three-wave mixing processes. This programmability also allowed us to employ closed-loop in situ optimization to compensate for phase mismatch in complex waveguide structures, such as width-modulated waveguides and spiral waveguides exceeding 10 cm in length. Furthermore, we show that programmable nonlinearity enables powerful in situ diagnostics, including direct dispersion measurements of various transverse modes and on-chip wavefront phase tomography. Our work opens up the possibility of building cascaded nonlinear nanophotonic systems where yield issues due to fabrication variations can be sidestepped while retaining the benefits of etched waveguides such as confinement and dispersion engineering.
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All authors Benjamin A. Ash, Ryotatsu Yanagimoto, Mandar M. Sohoni, Yang Xu, Yiqi Zhao, Martin M. Stein, Fan O. Wu, Marc Jankowski, Logan G. Wright, Tatsuhiro Onodera, Peter L. McMahon

Optics · Cross-listed from gr-qc

Analogue black hole lightring and its resonances in an optical fiber

R. Terrier, J. Fatome, B. Kibler et al. (+1 more)

We demonstrate the complete observation of a black-hole lightring resonance in an optical analogue. To do so, we generalize the concept of the photon sphere to non-stationnary systems by showing that the lightring is associated to a spatiotemporal caustic and that its complex frequency is determined by the propagation and divergence of this caustic. For an optical soliton acting as an analogue black-hole potential, we predict a characteristic spectral plateau whose boundaries are set by the real part of the lightring frequency, while its spectral decay is governed by the imaginary part. Using a pump-probe experiment in a 5-km-long dispersion-shifted fiber, we observe these signatures for two distinct pump wavelengths. The measured spectra agree with numerical simulations and with the predicted lightring-mode profile, providing direct access to both the oscillatory and decay properties of the resonance. Our results establish a direct experimental connection between black-hole lightrings, spacetime caustics, and quasinormal-mode spectroscopy in a dispersive analogue system.
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All authors R. Terrier, J. Fatome, B. Kibler, T. Torres

Optics · Cross-listed from physics.flu-dyn

Femtosecond laser-induced cavitation seeds liquid-jet breakup beyond the Rayleigh-Plateau stability limit

Sourabh Singh, Tamanna, S. Sree Harsha et al. (+1 more)

The Rayleigh-Plateau instability predicts that infinitesimal perturbations of a liquid jet grow only for kR < 1, with kR = 1 marking the classical stability boundary. Here, we show that femtosecond-laser-induced cavitation generates a localized, impulsive recoil perturbation on a flowing liquid jet, enabling a two-dimensional map of jet breakup across the (kR, epsilon/R) plane. The perturbation's spacing (wavelength) and strength (amplitude) are set independently by the laser repetition rate and pulse energy, respectively. At low amplitudes, tuning the repetition rate recovers the classical Rayleigh-Plateau dispersion relation and its kR = 1 cutoff, while increasing the wavelength enables controlled generation of monodisperse droplet trains, bidisperse droplet populations, and ultimately isolated single droplets. Along the amplitude axis, low pulse energies produce a seed that amplifies only the imposed wavenumber, whereas above a critical energy Ec, the seed broadens to excite many wavenumbers simultaneously. At still higher amplitudes, we demonstrate deterministic breakup for kR > 1, extending to kR = 1.9, with laser-synchronized droplet production rates up to 0.2 MHz. These results establish localized femtosecond-laser-induced cavitation as a route to controlled Rayleigh-Plateau breakup both within and beyond the classical linear-stability boundary.
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All authors Sourabh Singh, Tamanna, S. Sree Harsha, Prashant Kumar Singh

Optics

Digitally enhanced Multi-wavelength Stabilization using a Passive Fiber Frequency Reference

Hilma Karlsson, Vaishali Adya, Robert L. Ward et al. (+1 more)

High-stability frequency stabilization between lasers is essential for applications such as precision metrology, frequency dissemination, and quantum communications. We demonstrate the use of code-based multiplexing of a passive fiber-based interferometer for frequency stabilization and transfer between lasers separated by 85 GHz in frequency using a single shared passive reference. Out-of-loop characterization places an upper bound of sub-kHz/$\sqrt{\text{Hz}}$ on the transferred frequency noise at Fourier frequencies above 40 mHz, with a differential fractional stability of $7\times10^{-13}$ at 1 second. We also demonstrate continuous laser tunability and characterize the residual length noise coupling. Finally, we provide a framework for scaling the architecture to higher laser counts, offering a pathway to scalable, frequency agile stabilization of multiple light sources without the overhead of an optical frequency comb.
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All authors Hilma Karlsson, Vaishali Adya, Robert L. Ward, Chathura P. Bandutunga

Optics

Measuring Geometric Phase based on Indefinite Causal Order in a Sagnac Interferometer

Lucas Marques Fagundes, Finlay Campbell, Richard Aguiar Maduro et al. (+4 more)

Sagnac interferometers are important tools for precision measurements. Cancellation of common-path noise ensures a high degree of stability against external perturbations, while their sensitivity to rotations provides the basis of laser gyroscopes. Here we highlight another, less explored feature of Sagnac interferometers: the fact that optical elements are traversed in reverse order for clockwise and counterclockwise propagating light components. This provides the opportunity to explore a classical realization of indefinite causal order, where the order of events within a sequence is not fixed. We explore this concept to identify the geometric phase associated with two non-commuting polarization operations with a single measurement. This idea may have applications for the rapid determination of polarization manipulations or optical activity within chiral media, but foremost it provides a geometric illustration of indefinite causal order.
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All authors Lucas Marques Fagundes, Finlay Campbell, Richard Aguiar Maduro, Renné Medeiros de Araújo, Stephen M. Barnett, Sarah Croke, Sonja Franke-Arnold