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Physics Physics Optics

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Friday 28 August

Optics · Cross-listed from quant-ph

Input-Output Analysis of Quantum Dot SUPER Excitation

Johannes Kerber, Christoph Hotter, Helmut Ritsch et al. (+1 more)

The Swing-UP of the quantum EmitteR population (SUPER) two-color pulsed excitation scheme allows for robust and close to 100% excitation of a two-level quantum emitter using only red detuned light. We analyze the underlying counterintuitive dynamics using a full quantum input-output description of the in- and outgoing light pulses for the case of two coherent free-space input pulses at realistic photon numbers. At the microscopic level, the SUPER mechanism exhibits its nonlinear three-photon Raman-type character, leading to a net photon-number change of $-2$ in one mode and $+1$ in the other, as was first guessed from cavity-enhanced model descriptions at low photon numbers. We confirm that in free space, a sufficiently high pulse photon number, much larger than one, is required to achieve high-fidelity inversion. To treat the large coherent-state amplitudes (photon numbers) relevant for SUPER, we extend the quantum input-output formalism to include a cumulant expansion approach. With an interaction-picture formulation, the few exchanged photons that govern the nontrivial dynamics enable direct full-quantum calculations in truncated Hilbert spaces, including treatments in a displacement frame and for initial Fock-state pulses.
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All authors Johannes Kerber, Christoph Hotter, Helmut Ritsch, Klaus Mølmer

Optics

Correlation Swapping: a correlator for independent thermal light sources

Wanting Hou, Jilun Zhao, Zhiyuan Ye et al. (+4 more)

Optical intensity correlation is a fundamental property of light and an essential resource for numerous optical applications. In this work, we introduce the concept of classical correlation swapping, a classical analogue of quantum entanglement swapping, to generate all-purpose spatial correlations between two independent thermal light sources. Using a spatially unresolved Mach-Zehnder interferometer and a medium variable, we theoretically and experimentally demonstrate the feasibility of the correlator with two distinct schemes for independent pseudo-thermal light beams. Notably, the resulting photon correlations can be readily tailored to exhibit either bunching (peak) or anti-correlated (dip) characteristics, with a significantly reduced number of post-selection measurements. Leveraging this classical correlator, we further demonstrate the first classical ghost imaging experiment using uncorrelated or unknown light. Numerical simulations also confirm that the correlator can not only operate well in other spatial degrees of freedom (e.g., orbital angular momentum) but also be used to establish specific spatial correlations between pseudo-thermal light sources possessing distinct correlation properties. This work opens a new avenue for harnessing uncorrelated classical light in correlation-based optical applications.
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All authors Wanting Hou, Jilun Zhao, Zhiyuan Ye, Hong-Chao Liu, Hai-Bo Wang, Jun Xiong, Kaige Wang

Optics

High-performance silicon-metal laser welding resisting extreme conditions

Jiawei Yin, Markus Blothe, Hagen P. Kohl et al. (+3 more)

Reliable material joining is essential for countless industrial applications. While femtosecond laser welding provides a route beyond conventional bonding methods, demonstrations of silicon-metal joints are rare due to nonlinear propagation effects and have so far been limited to shear joining strengths of a few MPa. Here, we demonstrate high-strength silicon-Kovar laser welding using sub-nanosecond pulses. By optimizing the focal position, the welding pattern, the laser polarization, and the metal roughness, remarkable shear joining strengths up to 15.8 MPa are achieved. The silicon-metal joints withstand temperatures of up to 500 {\deg}C and are hermetically sealed. Together with the remarkable strength values, the resistance to harsh environments underpins the applicability of silicon-metal welding in various fields including aerospace, nuclear science, and metallurgy.
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All authors Jiawei Yin, Markus Blothe, Hagen P. Kohl, Christina Schütze, Stefan Nolte, Maxime Chambonneau

Optics · Cross-listed from quant-ph

Optomechanical inertial reference for atom interferometry

A. Rajagopalan, K. Stolzenberg, D. Thomas et al. (+5 more)

Atom interferometers are among the most sensitive inertial sensors, yet deployment outside the laboratory is limited by vibration noise, conventionally mitigated by external sensors or bulky isolation. Here we demonstrate a hybrid inertial sensor which fuses an optomechanical resonator and an atom interferometer by exploiting the resonator's test mass as the interferometer's reference mirror. This allows for better correlation than with two separate sensors, whose unknown transfer function is replaced by the static response of one mechanical element. The resonator achieves a displacement sensitivity of $8.6\cdot 10^{-15}$ m/$\sqrt{\mathrm{Hz}}$ with suppressed 1/f noise and yields a minimum acceleration sensitivity of $1.1\cdot10^{-6}$ m/s$^2$/$\sqrt{\mathrm{Hz}}$ over a bandwidth extending from sub-Hertz to 2.5 kHz. Under ambient laboratory conditions the integrated system removes vibration-induced phase ambiguity for accelerations up to $50\cdot 10^{-3}$ m/s$^2$ and reaches the interferometer's technical noise limit, which a commercial force-balance accelerometer does not. Because the resonance-tracking readout is largely independent of the mechanical design, the architecture transfers directly to other precision sensing platforms.
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All authors A. Rajagopalan, K. Stolzenberg, D. Thomas, A. Herbst, S. Abend, E. M. Rasel, F. Guzmán, D. Schlippert

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

Crystal-phase quantum dots in AlGaAs nanowires

Rohan Radhakrishnan, Rodion Reznik, Gilles Patriarche et al. (+6 more)

Crystal-phase quantum dots (CPQDs)$\unicode{x2014}$quantum dots in nanowires defined by crystal structure rather than material composition$\unicode{x2014}$constitute the only platform capable of fabricating quantum-dot arrays with the ultimate precision of a single atomic layer. This intrinsic control yields perfectly aligned quantum dots with atomically sharp interfaces, providing a unique pathway toward scalable quantum-dot-based photonic quantum technologies. To date, CPQDs have been studied primarily in binary semiconductors, such as InP and GaAs, where their emission linewidths are typically in the meV range, thereby limiting their technological potential. Here, we report, for the first time, CPQDs in AlGaAs nanowires and show bright single-photon emission with linewidths as narrow as 61 $\mu eV$ and low background emission, demonstrating optical quality well beyond typical CPQDs. We attribute this performance to a type-I band alignment, as suggested by an exciton lifetime of 1 ns, significantly shorter than that typically observed in type-II CPQDs. Additionally, we observe an exciton fine-structure splitting and a Zeeman splitting, as commonly observed in standard type-I self-assembled quantum dots.
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All authors Rohan Radhakrishnan, Rodion Reznik, Gilles Patriarche, Lorenzo Leandro, Igor Ilkiv, Anna Andreeva, Artem Khrebtov, George Cirlin, Nika Akopian

Optics

Structural perturbation theory for bound states in the continuum via bifurcation of zeros and extrema of the dispersion relation

Lijun Yuan and Ya Yan Lu

In a lossless periodic structure, a bound state in the continuum (BIC) corresponds to a real zero and a local maximum of the imaginary part of a complex dispersion relation $k = k(\beta)$, where $\beta$ is the Bloch wave number. A perturbation of the structure deforms the dispersion curve and may destroy, move or split the BIC, as demonstrated in existing studies involving lossless symmetry-preserving perturbations, symmetry-breaking perturbations and dissipative perturbations. We present a comprehensive perturbation theory, emphasizing the evolution of the real zeros and extreme points of $\mathrm{Im}[k(\beta)]$ under various structural perturbations. In particular, our theory reveals the existence of lasing threshold modes (LTMs), which are also zeros of $\mathrm{Im}[k(\beta)]$ when the perturbation involves gain with or without balanced loss. Using local Taylor expansions and Puiseux series, we determine the number, locations, and leading-order scaling of real zeros and extreme points for various types of BICs under different types of structural perturbations. The theory recovers known results and predicts new behavior for super-BICs under $\mathcal{PT}$-symmetric perturbations. Specifically, a propagating super-BIC corresponding to a fourth-order zero of $\mathrm{Im}[k(\beta)]$ splits into two real zeros representing either two BICs or two LTMs, and a symmetric standing wave splits into two BIC-LTM pairs. Our theory provides a general framework for studying BICs and nearby resonant modes in both lossless and non-Hermitian periodic structures.
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Optics · Cross-listed from physics.ins-det

Full-field fluorescence computed tomography (F3CT) using a calibrated virtual cone-beam pinhole geometry

Thomas Zillhardt, Yunhui Chen, Alexander Rack et al. (+4 more)

We present F3CT, a synchrotron-based hyperspectral full-field fluorescence computed tomography technique that avoids raster scanning by combining a pinhole aperture with an energy-resolving 2D detector. A virtual cone-beam model and two-stage calibration-reconstruction workflow enable 3D elemental mapping under full-field illumination. The method is demonstrated on biological and geological specimens, resolving silver-stain distributions in zebrafish tissue and high-energy fluorescence signatures in rock cores. Phase-contrast tomograms acquired sequentially under the same experimental geometry provide co-registered structural context. F3CT provides a high-throughput route to 3D XRF imaging and establishes a foundation for correlated structural and chemical tomography, with potential for future in-situ and operando implementations.
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All authors Thomas Zillhardt, Yunhui Chen, Alexander Rack, Matthew Veale, Matt Wilson, Philip J. Withers, Nicola Viganò

Optics

Quantum many-body effects in the optical response of ideal thin films

David Trejo-Garcia, Tapio T. Rantala, Marco Ornigotti et al. (+1 more)

We study quantum many-body effects in the long-wavelength optical response of confined electrons at finite temperatures. We simulate homogeneous electron gas confined in one dimension into a slab of nanoscale thickness. We demonstrate how the slab boundaries break down the ideal Drude response of free charge carriers, giving rise to scattering effects due to both the surfaces and quantum many-body interactions. We use a recent path-integral Monte Carlo (PIMC) approach developed in [Tiihonen et al. Phys. Rev. A 113, 053711] to quantify these effects in high accuracy. We perform phenomenological fits to Drude and Drude-Lorentz models parameters, manifesting various trends of the optical response with physical parameters like density and temperature, and numerical effects like finite size and the quantum statistics.
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All authors David Trejo-Garcia, Tapio T. Rantala, Marco Ornigotti, Juha Tiihonen

Optics

AAA rational approximation for scatterometry of nanoscale gratings

Livius Leibl, Viktoriia Sytenko, Rana Demircioglu et al. (+2 more)

We investigate the applicability of AAA rational approximation to scatterometry-related response functions of nanoscale gratings. A silicon line grating with material dispersion is considered. We compare the convergence of AAA rational approximation with that of cubic spline interpolation as the number of frequency samples is increased. The results demonstrate the potential of rational approximation, consistent with the pole structure of the considered response function arising from resonance effects of the grating.
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All authors Livius Leibl, Viktoriia Sytenko, Rana Demircioglu, Leonid Beliaev, Felix Binkowski

Optics

Three-dimensional optical vortices in nonlinear Bessel waveguides

Carlos F. Sánchez, Humberto Michinel, Boris Malomed et al. (+2 more)

We explore the formation, stability, and propagation dynamics of light bullets carrying orbital angular momentum (vorticity) in Bessel-structured nonlinear graded-index waveguides. While these waves are prone to the collapse in uniform three-dimensional media, we demonstrate that their stabilization is provided by a squared-Bessel index profile in the plane orthogonal to the propagation direction, which may play the role of the waveguiding or antiwaveguiding potential. Different solution families are obtained, revealing a variety of power-vs.-propagation-constant diagrams, characterizing the coexistence of multiple families. We analyze the propagation dynamics in a wide experimentally accessible parameter range. Our results contribute to the understanding of nonlinear light localization in multidimensional settings and suggest new possibilities for using structured light in advanced photonic applications.
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All authors Carlos F. Sánchez, Humberto Michinel, Boris Malomed, Ángel Paredes, José R. Salgueiro

Optics

Performance Optimization of Short Reach Optical Interconnects based on Direct Detection

Luca Poì, Stella Civelli, Marco Secondini et al. (+11 more)

Short-reach optical interconnects are evolving toward data rates beyond 400 Gb/s per lane, driven by the bandwidth and energy-efficiency requirements of AI-enabled datacenter networks. At these operating speeds, channel impairments, device nonlinearities, and hardware constraints limit the effectiveness of conventional transceiver design and digital signal processing (DSP). This paper presents a unified framework for the optimization of direct-detection optical interconnects, encompassing digital surrogate modeling, receiver-side DSP optimization, and end-to-end (E2E) transceiver learning. The proposed formulation provides a common perspective for model-based and machine-learning-based approaches, including linear and nonlinear equalization, lookup tables, decision trees, neural-network receivers, and E2E optimization. Their performance is discussed together with computational complexity and hardware implementation aspects, highlighting the associated trade-offs. We show, through simulations and experimental validations, that for a 40~Gb/s 10~km link, decision trees can outperform by 0.5–1~dB conventional linear equalization, with negligible hardware requirements. Moreover, we show that an E2E technique based on transformers can provide a gain up to 6~dB, highlighting the potential of joint transceiver optimization to improve the performance of next-generation short-reach optical links.
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All authors Luca Poì, Stella Civelli, Marco Secondini, Li Zhang, Dario Cellini, Asfand Nizamani, Ramin Solaimani, Lorenzo De Marinis, Mareli Rodigheri, Pantea Nadimi Goki, Muhammad A. Naz, Giampiero Contestabile, Enrico Forestieri, Fabio Cavaliere

Optics

Self-partitioned Interfacial Time Crystals

Joseph Huang and Yi Yang

Nonequilibrium many-body systems can spontaneously break symmetry in time, as in time crystals, or in space, through self-organized domains and interfaces. Whether these two forms of symmetry breaking can intertwine so that an emergent interface alone hosts time-crystalline order remains unknown. In this work, by introducing the Rabi-Hatano-Nelson model, we unveil the existence and mechanism of a self-partitioned interfacial time crystal (SPITC), where a homogeneous system generates its own internal and tunable interface, at which the time-translation symmetry is also spontaneously broken. Such a SPITC phase is intrinsically induced by nonreciprocity and open boundary conditions, without external pumping or long-range interaction. The periodic and open boundary phase diagrams of the system are both mapped out; vacuum and Dicke-like superradiance with static or active orders are identified, with analytical phase boundaries in the weak coupling limit. The frequency of the SPITC is found to scale quadratically with the spin-photon coupling strength, as we derive analytically for the slow dynamics of the spins. The position of the SPITC boundary scales with a critical exponent of $-1$ as a function of the degree of nonreciprocity, in stark contrast to $-1/2$ for an otherwise stationary boundary. Our construction of SPITC establishes a route to spatiotemporal order in non-Hermitian many-body systems.
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Optics · Cross-listed from astro-ph.IM

Broadband heterodyne interferometry with a chirped femtosecond laser in the H-band

Félix Gudin and Nicolas Forget

Infrared heterodyne interferometry offers a scalable alternative to direct interferometry for long-baseline telescope arrays. However, at near-infrared wavelengths, its sensitivity is limited by the electronic detection bandwidth and shot noise from the optical reference. Parallel detection via spectral multiplexing has long been identified as a potential means to increase the signal-to-noise ratio of heterodyne interferometers. We propose a new heterodyne detection architecture based on highly dispersed broadband pulses from a mode-locked laser, fast photoreceivers, and numerical correlation. This enables straightforward spectral multiplexing with commercial components to increase the SNR, while extending instantaneous wavelength coverage to simultaneous J- and H-band operation. The scheme also supports high-resolution spectroscopic imaging ($R \simeq 10^{3}-10^{4}$). We derive the SNR of a two-arm heterodyne interferometer based on balanced photodetection and apply the model to the proposed scheme, using measurements from a single-spectral-channel, all-fiber interferometer operating at 1.56 micrometer over an 8 nanometer bandwidth. We experimentally demonstrate an SNR exceeding 2 for a spectral flux density of 188 pW/nm, with an integration time of 0.4 ms. Scaling the integration time and number of spectral channels suggests that fringe visibility of the brightest H-band stars could be achieved with 1 m$^2$ telescopes within the typical atmospheric coherence time. These results represent a significant step toward broadband, scalable heterodyne interferometers, demonstrating the potential of ultrafast laser and telecommunications technologies for astronomical interferometry in the J+H bands. By combining broadband spectral multiplexing with numerical correlation, the architecture also opens a route to direct spectro-imaging without an additional spectrometer.
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Optics

Density-gradient effect in high-harmonic generation in gases

Zoltán Filus, Tímea Grósz, Chinmoy Biswas et al. (+6 more)

High-harmonic generation (HHG) in gaseous targets is the most widespread method to produce coherent extreme-ultraviolet (XUV) pulses with sub-femtosecond duration. However, this process has intrinsically low efficiency, and substantial research and development is devoted worldwide to increase the achievable photon flux through this highly nonlinear light–matter interaction process. In this work, we show the strong interplay of phase matching and absorption in gas-pressure gradients, substantially affecting macroscopic HHG efficiency. Through detailed experimental analysis and supporting numerical studies, we highlight their significance, particularly at the boundaries of the interaction volume. The concluded results have implications in the massively expanding application possibilities of HHG sources requiring high photon flux, for example in the semiconductor industry, in nanoscale imaging of biological and industrial samples, or in nonlinear optics in the XUV regime.
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All authors Zoltán Filus, Tímea Grósz, Chinmoy Biswas, Lénárd Gulyás Oldal, Tamás Bartyik, Barnabás Gilicze, Subhendu Kahaly, Katalin Varjú, Balázs Major

Optics

Compact Variational Neural Networks for Spectral Inference from a Single Nonlinear 2D Perovskite Photodetector

Karl Jonas Riisnaes, Ned Thaddeus Taylor, Hoi Tung Lam et al. (+4 more)

Spectroscopy conventionally separates optical frequencies before detection, imposing persistent constraints on footprint, complexity and scalability. Here we establish an alternative paradigm in which the nonlinear optoelectronic dynamics of a single two-dimensional perovskite photodetector physically encode the incident optical field and machine learning performs the inverse spectral reconstruction. Using a planar fluorinated phenethylammonium lead iodide (F-PEAI) photodetector, we exploit wavelength- and irradiance-dependent current-voltage signatures arising from the coupled effects of photocarrier generation, trapping, interfacial transport and field-dependent carrier dynamics. A compact variational encoder-decoder preserves the functional and history-dependent structure of these responses by independently projecting forward and reverse voltage sweeps onto a truncated Legendre-polynomial basis before mapping them through a probabilistic latent representation to continuous spectral parameters. Trained on fewer than 400 experimental voltage sweeps, the model generalises to excitation wavelengths excluded from training, reconstructing wavelength with $R^2=0.958$ and a mean absolute error of 8.1 nm, while recovering log-normalised irradiance with $R^2=0.987$. Voltage-resolved analysis further reveals that wavelength and irradiance are encoded differently across the nonlinear device response, with distinct bias regions carrying complementary optical information. These results establish nonlinear material and interface dynamics as a computational resource for spectroscopy and point towards hardware-algorithm co-design in which materials, interfaces and inference architectures are engineered jointly to maximise information content, enabling compact spectroscopic systems without dispersive optics or detector arrays.
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All authors Karl Jonas Riisnaes, Ned Thaddeus Taylor, Hoi Tung Lam, Rosanna Mastria, Francesco Saverio Difeo, Monica Felicia Craciun, Saverio Russo

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

Multi-dimensional spectroscopy of mobile excitons in two-dimensional semiconductors

Ned Wheaton, Jeffrey A. Davis, Jesper Levinsen et al. (+1 more)

Multi-dimensional coherent spectroscopy (MDCS) goes beyond standard linear-response probes and provides a powerful tool for investigating correlations between quasiparticles such as excitons (bound electron-hole pairs). Here we present a microscopic theory of MDCS that accounts for the delocalized nature of excitons in two-dimensional semiconductors. In contrast to the more phenomenological few-level approaches typically employed for modelling MDCS, our theory features mobile excitons with continuous momentum degrees of freedom. We find that the energy continuum associated with exciton momenta is crucial for producing interaction-induced decoherence, as well as capturing the interference between different exciton-polaron quasiparticles in the case of charge-doped semiconductors. Crucially, our calculated MDCS spectra agree well with recent experiments on doped monolayer MoSe$_2$ [Hao et al., Nature Communications 8, 15552 (2017)], and they suggest that the interactions between exciton polarons depend strongly on phase-space filling effects, where exciton polarons compete for electrons. Our results demonstrate that microscopic approaches allow one to gain new insights from the fine structure of MDCS on two-dimensional semiconductors, and they illustrate the utility of microscopic approaches to modelling MDCS experiments more generally.
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All authors Ned Wheaton, Jeffrey A. Davis, Jesper Levinsen, Meera M. Parish

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

Subcritical bifurcation and on-off bistability in ballistic polariton condensates

Oleg I. Utesov, Soohong Choi, Pavel Kozhevin et al. (+11 more)

Dynamics of exciton-polariton condensates under continuous-wave incoherent Gaussian optical pumping is considered. It is shown that the conventional supercritical Stuart-Landau picture is invalid in a certain domain of the parameter space. For strong polariton repulsion from the reservoir and relatively small pump spots, the dynamics is adequately described by the quintic Stuart-Landau equation. The corresponding subcritical pitchfork bifurcation leads to condensate formation, accompanied by bistability between the trivial and nontrivial states over a finite pump-power range and a one-bit memory. Further increase of the repulsion parameter or decrease of the spot size breaks down the perturbative approach and leads to a peculiar self-trapping regime with complex dynamics. Experimental evidence of the emergence of the proposed behavior is provided. Our findings can be used to design polaritonic setups that exploit the predicted memory effect.
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All authors Oleg I. Utesov, Soohong Choi, Pavel Kozhevin, Min Park, Daegwang Choi, Hyungdo Lee, Alexey N. Osipov, Alexey V. Yulin, Se Kwon Kim, Yong-Hoon Cho, Igor S. Aranson, Hyoungsoon Choi, Anton V. Nalitov, Sergei V. Koniakhin

Thursday 27 August

Optics

Deterministic control over launching efficiency of higher-order hyperbolic phonon polaritons

Thiago S. Arnaud, John E. Buchner, Ryan W. Spangler et al. (+3 more)

Hyperbolic materials, which exhibit an extreme form of birefringence enabling the volume confinement and frequency-dependent propagation of deeply sub-diffractional optical modes, offer the opportunity for extreme confinement via the stimulation polaritonic modes, with substantially higher confinement obtained through the efficient excitation of of the higher-order (shorter wavelength) hyperbolic polaritonic modes, which they can support. However, while these higher-order hyperbolic polaritons (HO-HPhPs) form high-momentum ray-like propagation within the bulk, efficient excitation of these modes, especially in contrast to the long-wavelength lower-momentum surface polariton propagating modes, has remained a challenge. Critically, the large momentum mismatch between these modes and free-space light, alongside the spatial mismatch between the sub-diffractional scatterer and the distinct modal distribution of HO-HPhPs, lead to a suppressed launching efficiency of these higher-order modes, limiting their use in nanophotonic applications. Here, we report the experimental observation of a 10-fold enhancement in the excitation efficiency of HO-HPhPs through the use of subsurface scatterers over traditional surface scattering (e.g. a flake edge or gold launcher) within single-crystalline {\alpha}-MoO3 slabs. We employ full-wave numerical simulations to investigate the role of the spatial overlap between HO-HPhP modal distributions and the scatterer placement upon excitation efficiency. Furthermore, we develop a generalized process using transfer matrix method to selectively design modal HO-HPhP excitation, which advances the capabilities of HPhP multiplexing for on-chip applications.
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All authors Thiago S. Arnaud, John E. Buchner, Ryan W. Spangler, Maximilian Obst, Jon-Paul Maria, Joshua D. Caldwell

Optics

Extending Silicon Avalanche Photodetection Beyond $2~\mu$m by Direct GeSn Integration

M. R. M. Atalla, J. Bélec, E. Rahier et al. (+5 more)

Silicon avalanche photodiodes provide a technologically mature platform for sensitive photodetection, but their spectral response is intrinsically limited by the silicon bandgap. Extending their operation into the infrared requires the integration of narrow-bandgap absorbers while preserving efficient avalanche multiplication and compatibility with silicon processing. Here, we propose and demonstrate a monolithic approach that combines direct, buffer-free growth of GeSn on silicon with a lateral thin-junction separate-absorption-multiplication architecture. The GeSn layer, with a Sn composition reaching 6 at.%, extends optical absorption to a wavelength of $2.6~\mu$m, while avalanche multiplication is spatially confined to an ion-implanted silicon lateral junction. This separation enables independent control of infrared absorption and carrier multiplication without the thick Ge virtual substrates conventionally used for GeSn epitaxy. GeSn-on-Si avalanche photodiodes exhibit low pre-breakdown dark current, stable breakdown at 72 V independent of device diameter, and clear infrared photoresponse extending beyond $2~\mu$m. At 78 K, the devices exhibit external quantum efficiency exceeding 100%, reaching 163% at $1.55~\mu$m, providing direct evidence of avalanche multiplication. These results establish direct integration of narrow-bandgap group-IV absorbers with silicon multiplication regions as a scalable strategy for extending the spectral reach of silicon avalanche photodetection, opening a route toward monolithic infrared detectors for sensing, imaging, communications, LiDAR, and quantum photonics
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All authors M. R. M. Atalla, J. Bélec, E. Rahier, S. Koelling, K. Omambac, P. Daoust, S. Assali, O. Moutanabbir

Optics · Cross-listed from quant-ph

Topological Winding Readout of an Emergent Page-Wootters Clock

Hesam Zaravashan, Gabriele Gradoni and Mohsen Khalily

The Page–Wootters construction gives time a Hilbert space, representing it as an internal degree of freedom whose readings the rest of the system evolves with respect to. We ask whether such a clock degree of freedom can carry a topological invariant, and we propose a photonic architecture in which it does and in which the invariant can be measured. Signal–idler pairs from spontaneous four-wave mixing in a coupled microring array supply the clock–system partition, with the idler occupying a Rice–Mele band whose staggered coupling and detuning are cycled adiabatically around a gap-closing point. One cycle acts on that band as a rigid translation by \(C\) unit cells, times a geometric phase periodic in the crystal momentum, times a dynamical phase, an identity exact in the adiabatic limit and independent of the state on which it acts. The readout targets the winding of that geometric phase across the Brillouin zone. Reversing the traversal of the pump loop cancels the dynamical phase and isolates twice the geometric phase in a two-photon coincidence fringe, while energy anticorrelation lets a filter on the signal scan the clock momentum without touching the clock and supplies the phase reference relationally, in place of an external optical reference. The estimate is protected on two independent levels, by the gap against smooth deformation and by the digital character of the unwrapping against noise below a threshold. A parameter budget anchored to thin-film lithium niobate places the requirements within reach at a conservative operating point.
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Optics · Cross-listed from quant-ph

Diamond optomechanical crystals for high-frequency strain and comb generation

Elham Zohari, Waleed El-Sayed, Aria Jafari et al. (+5 more)

Quantum optomechanical technologies benefit from mechanical oscillators that are high-frequency, can be coherently driven, and are capable of coupling to other quantum systems. Diamond supports all of these criteria: its large elastic modulus increases mechanical resonance frequency, its low nonlinear optical absorption increases the allowed intensity of fields used for coherent optomechanics, and it hosts spin qubits that interact with mechanical modes. Here we demonstrate a diamond optomechanical crystal cavity that supports multiple mechanical resonances with $\sim$12 GHz frequency and high $Q_\text{m} \times f_\text{m}$ product that can be coherently coupled to multiple optical modes. By exciting this sideband resolved system into mechanical self-sustained oscillations, we generate a frequency comb spanning 143 GHz. Analysis of the comb spectrum, combined with systematic characterization of the system's optomechanical coupling, allows us to quantitatively show that its mechanical oscillation amplitude reaches 130 pm. This corresponds to a maximum total dynamic strain of $1.1 \times 10^{-3}$ that is sufficiently high for future demonstrations of optomechanical control of diamond spin qubits.
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All authors Elham Zohari, Waleed El-Sayed, Aria Jafari, Ahmas El-hamamsy, Peyman Parsa, Joseph E. Losby, Natália C. Carvalho, Paul E. Barclay

Optics

Ultra-Low-Loss Silicon Nitride on Sapphire for Broad-Transparency Nonlinear and Quantum Photonics

Abdur-Raheem Al-Hallak, Shuai Liu, Kailu Zhou et al. (+9 more)

The field of photonic integrated circuits (PIC) has flourished in the past two decades, fueling numerous cutting-edge applications across sensing, networking, data interconnect, and quantum information processing. As a guiding material for PIC, Si$_3$N$_4$ has seen extensive use for its ultra-low loss, broad transparency, and diversity in implementation across both thin and thick films. Although the standard, traditional silicon dioxide (SiO$_2$) on silicon (Si) substrates that underpin the majority of Si$_3$N$_4$ photonics face drawbacks in the form of long-wavelength transparency limited by SiO$_2$, high-stress deposition for anomalous dispersion thick-film Si$_3$N$_4$, and leakage loss to the Si layer for low-confinement thin-film Si$_3$N$_4$. Featuring increased long-wavelength transparency into the mid-infrared, low-stress deposition of Si$_3$N$_4$, and a low index, this work investigates sapphire substrates as alternate hosts for Si$_3$N$_4$ photonics with greater spectral coverage and reduced fabrication complexity. This work presents a robust method of fabricating ultra-low loss photonic integrated circuits on a 500-nm-thick Si$_3$N$_4$-on-sapphire platform, exhibiting record-low losses below $0.1 \rm \;dB/cm$. Implemented using this process are high-Q microrings with intrinsic quality factors in excess of $4.5\times10^6$ and coupled-ring photonic molecules to support nonlinear gain. Leveraging the achievable low loss and high-Q, this work further reports the first demonstration of Kerr-comb and soliton generation on the Si$_3$N$_4$-on-sapphire platform. These advances in loss, quality factor, and soliton generation on this versatile, broad-transparency platform pave the way for future work in spectroscopy and quantum-enhanced sensing across previously prohibited spectral regions for Si$_3$N$_4$ photonics with reduced fabrication complexity.
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All authors Abdur-Raheem Al-Hallak, Shuai Liu, Kailu Zhou, Jiangnan Liu, Shawn Chen, James Hu, Ruhi Yusuf, Christopher Rodriguez, Maya Sarram, Yiming Lang, Zetian Mi, Zheshen Zhang

Optics · Cross-listed from physics.atom-ph

Influence of Many-Body Dipole-Dipole Interactions on Excitation Transfer in a Dense Gas

A. A. Bobrov, S. A. Saakyan, B. B. Zelener et al. (+1 more)

We study non-radiative dipole-dipole induced excitation transfer in dense Rb vapour. We show that density dependence of characteristic time of the excitation diffusion changes from linear to non-linear for high Rb density. It is attributed to the breakdown of binary collisions approach to the dipole-dipole excitation transfer. It is shown that the observed result can be qualitatively described if the mean free path is replaced by mean interatomic distance for the chracteristic diffusion length.
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All authors A. A. Bobrov, S. A. Saakyan, B. B. Zelener, V. A. Sautenkov

Optics

Self-starting Dynamics in All-fibre All-Normal-Dispersion Thulium Mamyshev oscillator

Dennis C. Kirsch, Kirill Grebnev, Alberto Rodriguez Cuevas et al. (+8 more)

Ultrashort pulse formation from noise represents a fundamental self-organisation process in nonlinear dissipative systems and remains central to ultrafast photonics. Mamyshev oscillators offer a particularly valuable platform for investigating this phenomenon because they do not rely on conventional saturable absorbers. Instead, pulse formation is governed by self-phase modulation in normal-dispersion fibres combined with periodic offset spectral filtering. Achieving self-starting pulse formation in these systems is challenging, particularly at longer wavelengths, due to limited normal-dispersion components and the complex gain dynamics. This work reports, to the best of current knowledge, the first self-starting, all-fibre, all-normal-dispersion Thulium-doped Mamyshev oscillator operating near 1.9um. The cavity employs a compact Fabry-Perot design incorporating a dispersion-engineered Thulium-doped gain fibre, a highly nonlinear passive normal-dispersion fibre, and a pair of chirp-free broadband fibre Bragg gratings. The oscillator self-starts without external seeding or active modulation and stabilises noise-like pulse generation regime at a fundamental cavity repetition rate. Real-time measurements and numerical simulations reveal the build-up pathway from noise through transient multi-pulsing and pulse competition to a stationary noise-like envelope. Our results show that both tailored laser components and gain-medium-specific dynamics are essential for enabling self-starting ultrashort pulse generation in Mamyshev oscillators and for extending these laser concepts beyond the near-infrared, thereby facilitating the development of compact and robust shortwave infrared (SWIR) sources and new regimes of ultrafast self-organisation.
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All authors Dennis C. Kirsch, Kirill Grebnev, Alberto Rodriguez Cuevas, Mikhail E. Likhachev, Svetlana S. Aleshkina, M. V. Yashkov, Sonja Unger, Claudia Aichele, Adrian Lorenz, Auro Perego, Maria Chernysheva

Optics

Field-driven attosecond deflection of electron beams at the position of planar foils

Xiaofan Gui, Kenichi L. Ishikawa and Yuya Morimoto

While the coupling of free-electron beams and light has enabled the control of electron's quantum states and the generation of ultrashort electron pulses, it can distort the measured signal when probing a laser-driven sample with an electron beam. Here, we theoretically study optical-field-driven beam deflection that inevitably occurs at the location of a laser-excited sample. Treating electrons in a beam as classical point particles and focusing on thin planar samples, we conduct a systematic study of the instantaneous deflection amplitudes with respect to light polarization, material type, thickness, and interaction geometry. For s-polarized excitation fields, the deflection amplitude is strictly proportional to the excitation-field amplitude in a foil, making beam deflection unavoidable. Conversely, for p-polarized fields, a nontrivial relationship emerges between the deflection amplitude and the field amplitude due to the interplay of electric and magnetic fields coupled with the electron-light velocity mismatch. Crucially, we demonstrate that the deflection can be minimized even under high field strengths by selecting an optimal configuration for a given foil material and thickness. These findings provide key guidelines for designing future time-resolved imaging experiments using ultrashort electron beams.
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Optics

Cavity Solitons

W.J. Firth and G.K. Harkness

A driven optical cavity containing a nonlinear medium can support stable, soliton-like objects, bright non-diffracting spots of light on a uniform background. Importantly, the nonlinear medium need not support ordinary (propagating) spatial solitons, and cavity solitons have been both predicted and observed in a saturable absorber, and predicted to even exist in self-defocusing media. The history, present status, and physical interpretation of such cavity solitons is reviewed. Recent research predicts cavity solitons in semiconductor cavity models with properties interesting for applications to optical information processing. Cavity solitons are natural `bits' for spatial information, possessing both robustness and plasticity, and some potential applications of their unique properties are mentioned.
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Optics

Ultra-broadband transient absorption down to 200 nm enabled by soliton dynamics in gas-filled hollow capillary fibers

Pieter J. Brongers, Kyle Barlow, Deepjyoti Satpathy et al. (+3 more)

The deep ultraviolet (DUV) window (200-300 nm) is essential for the characterization of (bio)chemical and material systems through the UV signatures of nucleobases, amino acids, peptide bonds, many organic moieties, and wide bandgap transitions. However, extending ultrafast spectroscopy to the DUV to access the associated electronic and structural dynamics has largely remained elusive, due to the limited bandwidth and efficiency of common femtosecond DUV pulse sources. We now close this gap and demonstrate ultra-broadband femtosecond transient absorption (TA) spanning 200-800 nm, achieving unprecedented coverage of the entire DUV window. We generate supercontinuum probe pulses through soliton self-compression in a helium-filled hollow capillary fiber at a repetition rate of 20 kHz and fully suppress their high intrinsic intensity fluctuations via a correlation matrix referencing scheme. We thus achieve detector-noise-limited TA measurements with an exceptional resolution of 9 $\mu$OD in one second, and demonstrate these novel capabilities by resolving the ultrafast spin-crossover dynamics of a Fe(II) complex in the DUV. This work opens the path to unravel previously inaccessible photophysical and photochemical dynamics encoded in the DUV.
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All authors Pieter J. Brongers, Kyle Barlow, Deepjyoti Satpathy, John C. Travers, Christian Brahms, Malte Oppermann

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

Exceptional point induced by hyperbolicity in an electrostatic spherical shell

Álvaro Buendía, Marcelo S. Barreiro and Nuno M.R. Peres

Exceptional points (EPs) are non–Hermitian degeneracies at which both eigenvalues and eigenvectors coalesce, usually engineered through balanced gain and loss or non–reciprocity. In this work, we show that the radial electrostatic problem of an anisotropic core–shell nanoparticle realizes an EP without any of the alluded conditons. Written in the logarithmic radial coordinate, the problem is a Cauchy–Euler equation that maps onto a damped oscillator and, equivalently, onto a two-site Hatano–Nelson Hamiltonian, so that the non-Hermiticity is emulated in space rather than in time and the sole control parameter is the degree of dielectric anisotropy, $\varepsilon_t/\varepsilon_r$. The shell is passive, reciprocal, and lossless, yet it hosts an EP and a non–Hermitian phase transition governed by hyperbolicity alone. Beyond a hyperbolicity threshold the electric field inside the shell turns from monotonic decay into spatial oscillation, producing hotspots at intermediate radii which can be exploited to tailor fluorescence, strong coupling, sensing, or cloaking. More broadly, this establishes hyperbolic media as a platform to simulate non–Hermitian physics without gain, loss, or non–reciprocity.
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Optics · Cross-listed from cond-mat.mtrl-sci

The Effect of Geometry on Thermodynamic Response

Bojana Bokic, Sébastien R. Mouchet, Biljana Stankov et al. (+9 more)

At the nano- and microscale, various patterns influence and shape thermal and optical response, making them essential for the survival of various biological species. In addition, controlling thermal radiation is vital for a broad range of applications, such as thermal management, spectroscopy, optoelectronics, and energy conversion technologies. For this reason, there is strong pressure to elucidate the physics of thermal radiation at the nanoscale. In this article, we provide evidence that complex nanoscale geometries affect thermal management, leading to an unusual thermal response in heat-capacity measurements as a function of temperature. Beyond identifying the structural constraints associated with this unusual thermodynamic response, the current study introduces the possibility of shaping the apparent heat-capacity response through geometry without necessarily altering the system's chemistry.
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All authors Bojana Bokic, Sébastien R. Mouchet, Biljana Stankov, Sanja Ostojic, Nicolas Roy, Darko Vasiljevic, Yin Chang, Marija Radmilovic-Radjenovic, Branislav Radjenovic, Thierry Verbiest, Mohamed Hatifi, Branko Kolaric

Optics · Cross-listed from physics.app-ph

Split Coaxial Cable Medium for Tunable Artificial Dielectrics and Plasmas

Alexander Zhuravlev, Jim A. Enriquez, Pavel A. Belov et al. (+1 more)

We introduce the Split Coaxial Cable Medium (SCCM), a mechanically tunable, capacitively loaded wire medium supporting artificial-dielectric and artificial-plasma Bloch regimes with high in-plane isotropy. Its unit cell comprises coaxial conductors interrupted by axial gaps. Relative axial displacement continuously varies their capacitive overlap and series capacitance while preserving the transverse lattice geometry and leaving the unit-cell inductance approximately unchanged. Equivalent RLC parameters are derived directly from the geometry and incorporated into complementary analytical models. A spatially dispersive local-field model predicts the Bloch dispersion and isofrequency contours, whereas a multilayer homogenization model provides the modal impedance, closed-form estimates of the low-frequency Bloch refractive index and plasma frequency, and loss-inclusive finite-slab scattering. Full-wave eigenmode and finite-slab simulations validate the predictions. Over the investigated displacement range, simulations yield tunabilities of $46\%$ in the low-frequency Bloch refractive index, from $n_{0,\min}=1.42$ to $n_{0,\max}=2.28$, and $21\%$ in the plasma frequency, from $f_{\mathrm{p},\min}=9.45~\mathrm{GHz}$ to $f_{\mathrm{p},\max}=11.61~\mathrm{GHz}$, while confirming high in-plane isotropy near the $\Gamma$ point in both regimes. These characteristics make the SCCM promising for gradient-index devices, directive antennas, and tunable plasma haloscopes.
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All authors Alexander Zhuravlev, Jim A. Enriquez, Pavel A. Belov, Juan D. Baena