Atomic Physics · Cross-listed from cond-mat.quant-gas
Imaging the vacuum fluctuations of a quantum field
Yansheng Zhang, Feiyang Wang, Yi Jiang et al. (+5 more)
Heisenberg uncertainties lead to inevitable fluctuations in the measurement outcomes for
quantum-mechanical observables. For
quantum fields, these uncertainties result in random spatial structures in snapshots of a field, even when the field is in its ground (
vacuum) state. Such `
vacuum fluctuations' are at the heart of a wide range of phenomena, from spontaneous decay processes to the Casimir force and Hawking radiation. Their existence is a key manifestation of the quantumness of the physical world, but usually it is only their consequences that are directly observed. Here, we directly observe spatial
vacuum fluctuations of a bosonic
quantum field. Our experiments are based on a homogeneous planar atomic Bose–Einstein condensate. The condensate comprises two coherently coupled interacting components (
spin states), and the
quantum field describes its
spin degrees of freedom. In the regime where the interactions dominate over the coherent coupling, our system emulates a (massive relativistic) sine-Gordon field. Images of the field reveal simultaneous fluctuations on different length scales, with scale-dependent amplitudes consistent with theoretical predictions for a
vacuum state. Observing such fluctuations in the sine-Gordon limit opens many possibilities for laboratory simulations of relativistic fields in regimes that are presently not theoretically tractable.
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All authors Yansheng Zhang, Feiyang Wang, Yi Jiang, Alexander C. Jenkins, Paul H. C. Wong, Christoph Eigen, Gehrig Carlse, Zoran Hadzibabic
Optics
Computational Methods of Wave Propagation for Semiclassical Models of High Harmonic Generation in Bulk Solids
Ava N. Hejazi, Nicholas Karpowicz, Gregory D. Scholes et al. (+1 more)
We present a theoretical framework for self consistent treatment of nonlinear light-matter interactions in the ultra-fast strong-field regime based on numerical solution of Maxwell's equations and
semiconductor Bloch equations. This framework is shown to describe high-order harmonic generation and propagation in bulk
semiconductors, investigating differences in reflected and transmitted harmonic spectra due to propagation effects. We show that the propagation of the combined field of the driving
laser pulse and generated harmonics in a bulk
semiconductor significantly modifies the harmonic spectra, affecting interpretation of experimental results relating the transmitted harmonic spectra to the underlying electronic structure of the material. This model allows the self-consistent description of strong-field light-matter interactions in the non-perturbative regime, opening the way to explore the transition between fully classical and
quantum regimes of interaction, tunneling and multiphoton regimes of material ionization, and perturbative and non-perturbative regimes of harmonic generation in bulk materials.
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All authors Ava N. Hejazi, Nicholas Karpowicz, Gregory D. Scholes, Julia M. Mikhailova
Plasma Physics
Excitation of the lower-hybrid drift instability in the outflow of electron-only magnetic reconnection
B. K. Russell, K. Sakai, Y. Zhang et al. (+17 more)
We report experimental evidence for the lower-hybrid drift instability in the current sheet normal direction of electron-only
magnetic reconnection. In our
laser-driven capacitor-coil experiment, the system size ($\sim$3 ion skin depths) places it in the electron-only regime. Yet, Thomson scattering reveals out-of-plane electron drift oscillations at the local lower-hybrid frequency, with kinetic energy density reaching $\sim$18% of the local
magnetic energy density. Linear theory with the measured parameters predicts more than ten e-folding times of growth, indicating that the instability reaches the nonlinear regime within the measurement window. Supported by particle-in-
cell simulations, these results demonstrate the importance of ions in the dissipation and energy transfer in electron-only reconnection where their significance has not been previously recognized.
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All authors B. K. Russell, K. Sakai, Y. Zhang, L. Gao, E. G. Blackman, W. Daughton, C. Dong, J. Katz, S. R. Klein, C. C. Kuranz, X. Li, X. M. Li, A. L. Milder, J. Ng, K. Orr, G. Pomraning, J. P. Schell, A. Stanier, J. Yoo, H. Ji
Atomic Physics · Cross-listed from quant-ph
Programmable cavity QED with a fiber-integrated atomic array
Stephan Roschinski, Johannes Schabbauer, Franz von Silva-Tarouca et al. (+3 more)
Strong atom-
photon interactions in optical cavities are a key resource for
quantum information processing,
quantum networking, and the exploration of
quantum optical effects. Optical tweezer arrays offer scalable, site-resolved control of neutral atoms, but their integration with high-cooperativity cavity QED systems remains challenging. Here we combine a twelve-site $^{87}$Rb optical tweezer array with a high-cooperativity fiber Fabry-Pérot microcavity. The array is positioned within the cavity mode and individual sites are controlled with subwavelength precision, enabling continuous tuning of the single-atom coupling strength via deterministic displacement through the standing-wave field. For up to five atoms coupled to the cavity, we measure collectively enhanced
vacuum Rabi splitting and implement cavity-based non-destructive readout of the number of coupled atoms. These results establish a scalable architecture for cavity-mediated
entanglement generation and many-body cavity QED with single-atom control, and they lay the foundation for fiber-integrated
quantum network nodes.
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All authors Stephan Roschinski, Johannes Schabbauer, Franz von Silva-Tarouca, Marvin Holten, Damien Bloch, Julian Léonard
Optics
Point Spread Function Engineering Using Implicit Neural Representations
Suet Ying Chan, Mitchell Gilmore, Qilin Deng et al. (+4 more)
Point spread function (PSF) engineering through pupil plane modulation is a technique used in microscopy to achieve specific imaging properties, such as depth encoding or extended depth of field. Existing PSF design methods often rely on extensive domain knowledge and task-specific basis functions, making it difficult to generalize across different applications. We treat the PSF engineering task as a phase
retrieval problem and propose a neural field pupil design method that optimizes a phase profile for any arbitrary, user-defined 3D PSF distribution. This provides a flexible framework for 3D PSF engineering for various applications with implicit regularization that proves robust to initialization compared to pixel-wise optimization methods
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All authors Suet Ying Chan, Mitchell Gilmore, Qilin Deng, Guorong Hu, Joseph Greene, Ruipeng Guo, Lei Tian
Chemical Physics
Vibrational Activation Triggers Ultrafast Excited State Intramolecular Proton Transfer in Single-Benzene Fluorophores
Brieuc Le Dé, Simon Huppert, Riccardo Spezia et al. (+1 more)
Single-benzene fluorophores (SBFs) are exceptionally light-weight
quantum emitters which have recently been shown to display Excited State Intramolecular
Proton Transfer (ESIPT) and highly tunable dual-fluorescence that could be exploited for multiple applications. Here, we employ excited-state molecular dynamics to investigate the ultrafast dynamics of ESIPT in two different SBFs, one of which with a new structure proposed in this work. We find that both single and double ultrafast
proton transfers can be triggered by exciting specific molecular vibrations. Strikingly, the kinetic activation of these vibrations - selected by atomistic,
symmetry-based analysis - can considerably enhance the yield of
proton transfer(s), as well as direct the reaction towards either single or double-transfer products. In-depth analysis elucidates the origins of this vibronic control, providing atomistic guidelines through which both the rate and fate of ESIPT could be steered using ultrafast IR-Vis spectroscopies.
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All authors Brieuc Le Dé, Simon Huppert, Riccardo Spezia, Alex W. Chin
Applied Physics
Acoustic Resonance Distribution for Core-Shell Scatterers
Naruna E. Rodrigues, Gilberto Nakamura, Odemir M. Bruno et al. (+1 more)
Acoustic metamaterials can exhibit unusual effective properties through mechanisms such as energy localization and resonant behavior in their constituent building blocks. Here, we investigate the internal acoustic energy of fluid core-shell spheres and map how resonances emerge from the interplay between material contrasts and shell geometry. The resulting phase diagram reveals an organized resonant landscape across distinct impedance-contrast regimes. From this structure, we obtain two compact predictive relations: one for resonance existence and another for spectral recurrence of successive peaks. Together, they enable the rapid identification of material and
geometric combinations associated with targeted resonance responses. The framework is further tested against representative systems from the literature, reproducing their observed behavior. These results provide a physics-based route for screening and tailoring resonant core-shell building blocks before full-wave numerical simulations.
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All authors Naruna E. Rodrigues, Gilberto Nakamura, Odemir M. Bruno, Alexandre S. Martinez
Atomic Physics · Cross-listed from quant-ph
Nonthermal Dynamics of a One-dimensional Rydberg-atom Chain with Constraint Four-body Interactions
Tianyi Yan and Weibin Li
We investigate dynamics of a linear chain of Rydberg atoms driven by a constrained four-body interaction, where two neighboring atoms are excited simultaneously from the electronic ground state $|0\rangle$ to Rydberg state $|1\rangle$ only when their closest neighbors are in $|0\rangle$ state. By employing an ansatz for the many-body ground state, the low-energy
Hamiltonian is given by a tridiagonal form. The many-body ground state energy, which scales linearly with the chain length $L$, is obtained analytically in the thermodynamic limit and agrees with the one of the exact diagonalization. Our model supports
quantum many-body scar eigenstates that are nearly equally spaced energetically. The scar states overlap strongly with the basis state $|\mathbf{0}\rangle=|0\cdots 0\rangle$. We show that the overlap distribution is tilted by the state-dependent four-body interaction. This leads to non-ergodic dynamics, evidenced by the revival of the initial state. The four-body constrained model can be realized with Rydberg atoms in a Peierls array with alternating bond lengths, where atoms on the shorter and longer bonds experience Rydberg blockade and antiblockade, respectively. Our study provides a pathway to explore constrained non-ergodic dynamics with four-body interactions by combining the Rydberg blockade and antiblockade.
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Physics and Society
Growth Without Us: Machine Consumers, Corporate Circularity, and the Decoupling of GDP from Humanity after AGI
Sahil Sharma
The standard objection to full automation is demand-side: if humans earn nothing, who buys the output? This confuses an accounting role with a biological species. We model a post-AGI economy in which corporations own populations of AI and robotic
agents that are both producers and consumers of energy, compute, maintenance, and upgrades, traded among firms. Three results follow. (i) Demand closure: a closed inter-corporate economy with zero human consumption is not degenerate; it is the classical von Neumann expanding economy, whose growth rate is well defined, positive, and maximal precisely because all output is reinvested. (ii) Bottleneck removal: once economic
agents are manufactured rather than reared, the binding constraint on growth shifts from human demography (a ~20-year, non-parallelizable reproduction technology capped at a few percent per year) to fabrication throughput and energy capture, permitting growth one to two orders of magnitude higher, with
hyperbolic episodes when machine researchers raise their own productivity. (iii) Decoupling: output and human welfare separate completely, and the welfare relevance of arbitrarily large GDP collapses into one state variable: the human ownership share $\epsilon_t$ of the corporate network. A golden-rule decoupling
theorem sharpens this. At maximal growth the interest rate equals the growth rate (r = g), so any positive human consumption rate out of wealth makes $\epsilon_t$ decay exponentially at exactly that rate. The human share survives only if the machine economy runs strictly inside its expansion frontier, or if law forces it to. We characterize three terminal regimes – rentier post-scarcity, full circular decoupling, socialized ownership – and the instruments that select among them. The conclusion is narrow: in a post-AGI economy, employment policy is obsolete and ownership policy is everything.
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Computational Physics · Cross-listed from cond-mat.stat-mech
Splitting probabilities for Brownian motion with diffusing boundaries: Application to polymer translocation
Alexander K. Hartmann, Satya N. Majumdar and Alberto Rosso
We study the translocation of a
polymer chain through a nanopore where the chain length fluctuates stochastically due to the polymerization-depolymerization processes at the chain ends. We map this process to an equivalent representation where the pore performs a
stochastic random-walk-like process on a line in the presence of two diffusing sinks on either side of it with
diffusion constants $D_1$ and $D_3$ respectively. The translocation process terminates when the pore hits either of the two outer diffusing sinks. In the case where the pore motion itself is diffusive with
diffusion constant $D_2$, we compute exactly the splitting probability that the pore hits the left (right) sink before hitting the right (left) sink. We show that the splitting probability in the presence of mobile sinks is rather nontrivial compared to the classical case of immobile sinks (the latter corresponds to the case when the chain length is fixed). Furthermore, we also compute exactly the probability distribution of the translocation time and that of the chain length at the completion time of the translocation. We show that both distributions have power law tails with exponents that depend continuously on the
diffusion constants $D_1$, $D_2$ and $D_3$. We validate our analytical predictions via numerical simulations. We then present numerical results for the case when the pore performs a fractional Brownian motion with Hurst exponent $0<H<1$, while the sinks are still diffusive.
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Optics
Intensity-based scattering correction enables in vivo two-photon imaging beyond 1 mm
Yucheng Li, Renzhi He and Yi Xue
Optical imaging of the deep
brain with subcellular resolution is essential for neuroscience, but noninvasive imaging beyond the cortex, through scattering white matter and into the hippocampus, has generally required three-
photon microscopy at longer excitation wavelengths. Here, we introduce deep-learning-enhanced
Fourier-domain intensity coupling for scattering correction (DeepFOCUS), an intensity-based two-
photon approach that uses deep learning to compute intensity-modulation masks for real-time modulation of excitation light during image acquisition. Unlike deep-learning-based image restoration, this method directly improves image formation by computing intensity-modulation masks that shape the excitation light in real time, with each mask experimentally validated by the acquired fluorescence signal to avoid
hallucination artifacts. Using 1035 nm excitation, we achieved in vivo two-
photon imaging beyond 1 mm depth in the intact mouse
brain, resolving YFP-labeled
neurons and FITC-labeled blood vessels through the entire cortex and white matter down to the CA1 region of the hippocampus. DeepFOCUS extends two-
photon imaging to depths previously accessible mainly with three-
photon microscopy and could enable broader adoption of hippocampal imaging by upgrading existing two-
photon systems.
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Classical Physics · Cross-listed from cond-mat.mes-hall
Floquet Theory for Light-Driven Rotation of Dipolar and Multipolar Particles
Amane Takano, Minoru Kanega and Masahiro Sato
Nano- or micro-particle rotation driven by light has been well known in the fields of optical manipulation and optical physics since the end of the last century. It is viewed as a sort of angular-momentum transfer from light to material, but its microscopic analysis based on the
Hamiltonian or the equation of motion has been less developed. We model this rotation with a simple setup of an electrically dipolar or multipolar particle irradiated by circularly polarized
laser and comprehensively analyze the Langevin-type equation of motion by using the Floquet theory for dissipative classical systems and the mode separation method. Furthermore, we numerically compute the time
evolution of the particle. As a result, we accurately estimate the dependence of the
laser-frequency,
laser-intensity, particle mass, temperature, and friction (dissipation) on the
laser-driven rotation. We determine the “nonequilibrium phase diagram” of the
laser-driven rotation in a broad parameter regime, which consists of three regimes: the rotation frequency $\Omega\propto\omega^{-1}$, $\Omega\propto\omega^{-3}$, or $\Omega=\omega$ ($\omega$ is the
laser frequency). Comparing our theoretical result with some experiments, we show that the result of the overdamped Langevin equation is qualitatively consistent with the experiments.
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Chemical Physics
Observables and Anti-Hermitian Generators in Time-Dependent Unitary Coupled Cluster Theory
Martin A. Mosquera
This work presents a time-dependent (TD)
unitary coupled-cluster (UCC) formulation for electronic
quantum dynamics, including the propagation of excited states and their superpositions, in both single- and multi-reference regimes. Standard TD coupled-cluster techniques offer size-extensivity, but they rely on non-Hermitian bivariational action functionals that break time-reversibility, giving transition
matrix elements and amplitude
estimators that are asymmetric (though accurate and systematically improvable). Here we use the time-
evolution operator as an exponential map driven by TD anti-Hermitian cluster operators and first-order generators. Applying the Dirac-Frenkel action principle, we extract equations of motion governed by Heisenberg-picture-like commutators. This approach connects to our previous non-Hermitian formulations, where observables are expressed in terms of regular and extended cluster operators. From that connection we obtain a generator cluster operator whose unperturbed TD limit leads to the UCC
eigenvalue problem. Even though this problem can be exact, the time dependence of the generator holds only at short propagation times, so we use the generator to prepare the initial state and then propagate that state with the formal TD UCC equation of motion. The theory is tested on an extended hard-core Bose-Hubbard ring with connections to neutral atom chains, and we discuss the theory's present limitations and possible extensions.
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Chemical Physics
Incorporating multiscale mechanics in lithium-ion battery models
Andrea Giudici, Andres F. Galvis, Smita Sahu et al. (+4 more)
Lithiation-induced swelling in lithium-ion batteries generates stresses not only within active particles, but also across the surrounding non-active
matrix, electrodes, and
cell stack. These stresses can modify the chemical potential of lithium and therefore influence transport, reaction kinetics, and terminal voltage. We derive a reduced-order electro-chemo-mechanical model that captures this multiscale coupling while retaining a complexity comparable to standard Doyle–Fuller–Newman models. The electrode is modelled as a periodic array of spherical active particles embedded in a homogenised elastic non-active
matrix. Exploiting the small stiffness of the non-active
matrix relative to the active material, together with scale separation between particles, electrodes, and the full
cell, we obtain an effective mechanical correction to the active-particle chemical potential and overpotential. This correction depends on particle swelling, electrode-scale strain, and macroscopic boundary conditions such as clamping or applied pressure. The resulting formulation can be incorporated directly into DFN, SPMe, and SPM frameworks, providing a computationally efficient route to include battery-scale mechanical effects in electrochemical simulations.
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All authors Andrea Giudici, Andres F. Galvis, Smita Sahu, Robert Timms, Colin Please, Jon Chapman, Jamie M. Foster
Optics
Wavefront shaping of terahertz radiation using two-color flying-focus pulses with time-dependent focal velocities
A.L. Elliott, H. Markland, K.G. Miller et al. (+3 more)
Properly phased two-color
laser pulses drive photoionization currents that emit broadband THz radiation. With a conventional two-color pulse, the ionization front travels at a nearly constant superluminal velocity, generating THz radiation with conical wavefronts at a Cherenkov-like angle. Here we show that the dynamic intensity peak of a two-color ultrashort flying-focus pulse can be used to control the shape of the THz wavefronts. Simulations demonstrate that non-uniform motion of the intensity peak and the ionization front it drives result in a time-dependent emission angle that determines the wavefront shape. A decelerating intensity peak, in particular, enables the generation of THz radiation with
parabolic wavefronts that are well suited for collection and focusing.
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All authors A.L. Elliott, H. Markland, K.G. Miller, S.W. Jolly, J.J. Pigeon, J.P. Palastro
Classical Physics · Cross-listed from quant-ph
Vacuum viscosity and relativistic inertia: Motion of a massive object with charged internal degrees of freedom interacting with a classical field
Jen-Tsung Hsiang and Bei-Lok Hu
Our present investigation into a rather rudimentary problem is motivated by two classes of problems studied since the 70's, cosmological particle creation and its more accessible analog, the dynamical Casimir effect on the one hand, and
quantum friction a neutral atom moving along a dielectric surface would experience, on the other. The backreaction effects of produced particles being able to isotropize the expansion of the universe, or to slow down the moving mirror can be understood via the concept of
vacuum viscosity arising from fluctuations of the
quantum field. We want to track down the origin of this effect by asking the question whether a moving massive $M$ object with a charged internal degrees of freedom $\chi$ interacting with a free unbounded classical field $\phi$ at zero temperature would experience a viscous force, similar to the said precedents. Adopting a microphysics model for optomechanics which can treat the unequal tripartite $\chi$-$\phi$-$M$ interactions, we first perform a nonrelativistic calculation, which seems perfectly legitimate considering the needs of atomic physics, and found the answer to be yes, but a relativistic covariant calculation says no. We identify where the nonrelativistic framework is defective. The resolution of this latent yet real conflict is technically nontrivial but physically quite inspirational. It results in added enriched contents to Newton's first and second laws when the principles of special relativity are enforced, and rules to follow to get the correct nonrelativistic answer
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History and Philosophy of Physics
Minkowski's Geometric Explanation of Lorentz Contraction
Tilman Sauer
Hermann Minkowski's original explanation of relativistic length contraction using a space-time diagram and conic section geometry of a standard hyperbola is reconstructed on the basis of unpublished manuscript notes dated to the spring of 1908. The manuscript notes likely reflect Minkowski's preparation of a lecture to physics and mathematics teachers. They reveal Minkowski as an educator as well as a promoter of a mathematization of the physical sciences. I also comment on his interpretation of Einstein's work and on the use of
language in his popularization of mathematics.
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Chemical Physics · Cross-listed from quant-ph
SAKE: Spectral Autodiff Kernel Expansion for Geometric Liouvillian Transport. A Differential-Geometric Framework for Response Transport in Quantum Dynamical Systems
Eric R. Bittner, Carlos Silva-Acuna, Hao Li et al. (+1 more)
We introduce the Spectral Autodiff Kernel Expansion (SAKE), a differentiable computational framework for transporting nonlinear spectroscopic response between neighboring
quantum dynamical models. Rather than recomputing multidimensional spectra independently for each
Hamiltonian or Liouvillian, SAKE constructs local transport expansions about a reference model by combining forward-mode automatic differentiation with Duhamel transport theory. Automatic differentiation generates first-, second-, and third-order derivatives of the parameter-dependent Liouvillian, which are assembled into a pathway transport operator that maps the nonlinear response of a reference model onto neighboring systems. The framework is validated for a four-level excitonic dimer possessing an $su(2)\times su(2)$
symmetry by comparing second- and third-order transported pathway operators with exact projected transport
matrices obtained from direct calculations. The third-order expansion accurately reproduces the projected transport operator and its associated pathway mixing. Beyond providing an efficient computational strategy, the transport operator reveals how coherent and dissipative perturbations redistribute amplitude among double-sided Feynman pathways, exposing mechanistic information that is not directly apparent from the nonlinear spectrum. SAKE thereby establishes a differentiable computational framework for nonlinear spectroscopy that supports efficient local parameter exploration, sensitivity analysis, and future inverse-design applications.
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All authors Eric R. Bittner, Carlos Silva-Acuna, Hao Li, Simon Paiva-Ortega
Optics
Symmetry-guided modal control in elliptical femtosecond-laser-written photonic waveguides
Tadas Paulauskas, Ubaid Ur Rehman, Eimantas Dermauskas et al. (+1 more)
Few-mode photonic
circuits can increase functionality without multiplying waveguide paths, but bends and fabrication errors can mix their transverse modes. We investigate a strategy in which waveguide confinement and perturbation parity are engineered together in vertically elliptical, femtosecond-
laser-written glass waveguides. The intended modal basis comprises the even $1S$ mode and the vertically odd $2P_y$ mode. No window-converged $2P_x$ state is resolved for a lower-confinement (LC) design, whereas a higher-confinement (HC) design guides $2P_x$, which must therefore be isolated by
symmetry. In scalar beam-propagation calculations, the $1S$-$2P_y$ propagation-constant splitting predicts the optimized periods of a vertically modulated coherent modal splitter to within $1.0\%$. Horizontal S-bends remain parity-mismatched for $1S \leftrightarrow 2P_y$ coupling, while the
symmetry-allowed HC $1S \rightarrow 2P_x$ transfer reaches only $0.6\%$ at the largest displacement. At a displacement of $150~\mu\mathrm{m}$, the HC design retains approximately the same $2P_y$ power as the LC design retains at $40~\mu\mathrm{m}$. Thermal and
stochastic writing-error calculations reveal the resulting trade-off: stronger confinement improves modal-power retention, but writing jitter that breaks $x$-parity can populate the guided $2P_x$ mode. These results demonstrate how modal-basis engineering can shift part of the crosstalk-control burden from the trajectory to waveguide
symmetry, supporting joint path–mode degrees of freedom in
quantum photonic applications.
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All authors Tadas Paulauskas, Ubaid Ur Rehman, Eimantas Dermauskas, Valdemar Stankevic
Optics
Geometric Control of Cat States in High Harmonic Generation
Arti Gaharwar, Rocío Borrego-Varillas, Marcelo F. Ciappina et al. (+6 more)
High-harmonic generation (HHG) provides a powerful platform for exploring the interaction between intense
laser fields and matter on ultrafast timescales. Beyond its conventional description in terms of emitted radiation and electron dynamics, a fully
quantum treatment of HHG reveals that the nonlinear light-matter interaction can modify the
quantum state of the driving field itself, establishing correlations between the fundamental and harmonic modes. This perspective opens new possibilities for using HHG as a tool to engineer and control nonclassical states of light. In this work, we investigate the
geometric properties of optical Schroedinger cat states generated in HHG via conditioning and post-selection. By analyzing the coherent-state displacements induced by different structured driving fields, we characterize the resulting phase-space
evolution and the associated
geometric phases of the generated
quantum states. Particular emphasis is placed on how the polarization and spatial-mode structure of the driving light influence the geometry and
evolution of displaced coherent states. Our results demonstrate that structured light offers a versatile means of controlling the
geometric dynamics of HHG-generated cat states across the parameter space. Furthermore, we discuss the prospects for realizing genuinely topological optical cat states by exploiting more complex structured light configurations.
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All authors Arti Gaharwar, Rocío Borrego-Varillas, Marcelo F. Ciappina, Anna G. Ciriolo, Javier Rivera-Dean, Philipp Stammer, Paraskevas Tzallas, Emilio Pisanty, Maciej Lewenstein
Medical Physics · Cross-listed from eess.IV
Flow Matching-Based PET Image Reconstruction
Fumio Hashimoto, Ziqian Huang, Tatsuya Yokota et al. (+1 more)
Generative models have shown strong potential for positron emission
tomography (PET) image reconstruction. Although
diffusion model-based reconstruction methods have demonstrated promising performance, they often require many reverse sampling steps with data-consistency updates incorporated into the sampling process. Flow matching offers an attractive alternative because it can directly estimate clean images from intermediate states, allowing data-consistency refinement to be separated from flow propagation. In this work, we proposed flow matching-based PET image reconstruction methods. We first established PET-FlowDPS by incorporating Poisson likelihood guidance with an expectation-maximization (EM)-based preconditioner into the FlowDPS framework. We then proposed a model-based PET reconstruction method that used a pretrained flow matching model as a prior, in which the flow-based prior, PET data refinement, and
stochastic propagation were interpreted within an approximate
Bayesian framework. Experimental results using [$^{\text{18}}\text{F}$]FDG
brain PET
datasets showed that the proposed method achieved better bias-variance trade-offs across different dose levels compared with other reference methods. These results demonstrated the potential of flow matching as a generative prior for quantitative PET image reconstruction.
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All authors Fumio Hashimoto, Ziqian Huang, Tatsuya Yokota, Kuang Gong
Applied Physics
Mid-infrared distributed-feedback lasing from black phosphorus under nanosecond excitation
Julien Brodeur, Laure Sène and Stéphane Kéna-Cohen
Mid-infrared (MIR) light sources compatible with silicon photonics are highly desirable for environmental sensing and free-space optical communications. Conventional GaSb-based
quantum-well and interband-cascade
lasers, however, rely on complex epitaxial
heterostructures, complicating their integration with silicon photonic platforms. Here, we demonstrate a room-temperature MIR surface-emitting distributed-feedback (DFB)
laser using black phosphorus (b-P) as the active gain medium. By deterministically integrating exfoliated b-P flakes onto lithographically patterned SiO$_2$ gratings, we obtain narrowband emission with a full width at half maximum below 3 nm under 1064 nm optical excitation. The lasing wavelength is tunable from 3.79 to 4.05$~\mu\text{m}$ through the b-P flake thickness, covering a technologically important region of the mid-infrared. Room-temperature thresholds as low as $(0.25 \pm 0.07)\ \text{mJ/cm}^2$ are achieved under nanosecond excitation. Upon cooling to 110 K, the threshold decreases tenfold to $(0.015 \pm 0.005)\ \text{mJ/cm}^2$. These results establish planar b-P DFB cavities as a promising platform for heterogeneously integrated MIR
lasers based on van der Waals
semiconductors.
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Biological Physics
Growth phases of an active tissue: determinate, indeterminate, and proportionate
Jigyasa Watwani, K. Vijay Kumar and Vishal Vasan
Growth may cease at a target size or continue throughout life: the determinate and indeterminate phenotypes. We develop an active viscoelastic continuum model of a tissue growing along one axis, in which
cell division and death generate active stresses. We find two asymptotic states: one in which the tissue reaches a relative size fixed by its material parameters, and one in which it elongates linearly without bound. Which state is realised is set by the ratio of active stress to elastic modulus. The transition originates in a bound on the elastic stress the tissue can support: a sufficiently large activity can never be balanced. In a tissue made of parts with different material properties, the growing phase settles into fixed length proportions, set by the mechanical impedances of the parts rather than inherited; matching impedances to initial lengths preserves the proportions the tissue began with. Determinate, indeterminate and proportionate growth thus appear as regimes of one continuum mechanical framework.
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Physics and Society
Climate change and human mobility will shape dengue emergence risk in Europe
Charley Presigny, Paolo Baglioni, Pietro Rotondo et al. (+3 more)
The risk of local arbovirus outbreaks in Europe is expected to increase due to
climate change, as suggested by the multiplication of arbovirus outbreaks in the last decades. Europe has historically been a non-endemic region, making it vital to pinpoint which populations are potentially exposed -and under which conditions- so we can build truly robust epidemic preparedness capabilities. We introduce an integrated, multi-scale model that fuses a mechanistic transmission engine with a vector abundance framework, all embedded in a mobility-driven metapopulation system capturing human, vector, and air-traffic movement. To this end, we combine
climate and population projections with mobility data to estimate and map dengue emergence risk in Europe throughout the 21st century. Additionally, we introduce a dedicated migration model that explores how
climate-driven population redistribution could alter these risk estimates.Assuming the
climate avoids major tipping points, model-derived risk indicators increase substantially under most emissions scenarios. While the spatio-temporal risk will remain largely driven by importation, our results indicate a gradual transition toward an environment-driven regime, particularly under the worst-case emissions scenario. To better anticipate and manage recurrent arbovirus outbreaks, our findings highlight the need to integrate mobility pathways and
climate-driven population redistribution into predictive models of vector-borne disease emergence in temperate regions.
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All authors Charley Presigny, Paolo Baglioni, Pietro Rotondo, Michele Allegra, Annalisa Barla, Manlio De Domenico
Chemical Physics
Nonzero-temperature vibronic spectra of polyatomic molecules from a zero-temperature classical trajectory
Davide Barbiero and Jiří J. L. Vaníček
By combining coherence thermofield dynamics with the single-Hessian approximation, we enable simulations of low- to medium-resolution vibronic spectra of weakly anharmonic systems at nonzero temperatures, at negligible additional cost relative to zero-temperature calculations. Single-Hessian coherence thermofield Gaussian wavepacket dynamics is exact in any harmonic potential, provided that the reference Hessian is that of the final surface. When applied to Morse systems of increasing anharmonicity and varying temperature, this method successfully captures excited-state anharmonicity and key temperature-dependent spectral features, including hot bands and broadening. By combining the method with on-the-fly ab initio dynamics, we demonstrate its utility by computing the absorption spectra of naphthalene, aminocoumarin C450, and phenyl radical, and the photoelectron spectrum of SeO$_{2}^{-}$ . Within the ab initio single-Hessian approximation, after the zero-temperature spectrum is obtained at the cost of classical molecular dynamics (on the order of hours), all nonzero-temperature spectra are computed in seconds.
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Plasma Physics
Symmetry-agnostic stellarators for collisionless confinement
W. Sengupta, A. Bhattacharjee and S. Buller
Quasisymmetry, omnigenity and piecewise omnigenity confine trapped particles by making the bounce action independent of the field-line label. Recent optimizations produce mixed-
symmetry stellarators that confine alpha particles well without them. We propose a general theory for them. From Whitham modulation theory we define iso-action, which requires only that the drift surface close and allows misalignment with flux surfaces. A solvable model supplies an exact relation between trapped segments while branch actions vary. We develop a proxy $\Gamma_W$ for the reach that misalignment costs.
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Atomic Physics · Cross-listed from quant-ph
Lensing and enhanced single atom detection via a single-pixel nanostructure
Ling-Xiao Wang, Lei Xu, Ai-Ping Liu et al. (+7 more)
We propose and demonstrate a general mechanism for nanoscale
lensing based on the phase gradient imposed by a single nanostructure scattering light in its near-field. We verify this effect using an optical waveguide on a substrate, with single atoms serving as
quantum probes that sample the near-field intensity through their fluorescence. This
quantum probing technique provides a unique, non-destructive approach to characterizing focused optical fields and reveals a 4-fold enhancement in single atom detection efficiency. This work establishes on-chip nanostructures as a multi-functional
quantum optics platform that can efficiently route
photons, localize fields, and enhance atom-
photon coupling, offering new opportunities for trapping and manipulating single atoms and realizing hybrid nanophotonic-atomic systems for
quantum applications.
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All authors Ling-Xiao Wang, Lei Xu, Ai-Ping Liu, Guang-Jie Chen, Yuan-Hao Yang, Jia-Qi Wang, Xin-Biao Xu, Guang-Can Guo, Chang-Ling Zou, Guo-Yong Xiang
Accelerator Physics
Electron energy gain in a dielectric laser accelerator as a function of the base angle of a triangular grating structure
O.O. Svystunov, A.V. Vasyliev, I.V. Beznosenko et al. (+2 more)
Dielectric
laser accelerators (DLAs) represent a compact and cost-effective alternative to conventional RF accelerators. Despite the various grating geometries already studied, a comprehensive investigation of triangular profiles, particularly the effect of the base angle of the saw-tooth grating profile, remains insufficient. This paper presents the results of numerical particle-in-
cell (PIC) simulations of electron acceleration in DLAs based on double gratings with a triangular profile. One of the gratings, onto which the
laser beam is incident, is transparent, while the second grating was either transparent or reflective for the
laser pulse. The geometry of the first grating was fixed. A systematic study was conducted on the influence of the base angle of the second grating ($\alpha = 5^\circ - 44^\circ$), its spatial orientation, the presence of a reflective gold coating, and the shape of the incident
laser pulse (plane wave versus Gaussian profile) on the acceleration rate. The results reveal a complex interplay between these parameters. For an electron beam with an initial energy of 10 MeV, a maximum accelerating rate of 345 MeV/m was achieved for the structure with a left-handed reflective grating and a base angle of $\alpha = 10^\circ$ when excited by a Gaussian pulse. Under plane-wave excitation, the left-handed reflective grating with $\alpha = 25^\circ$ provided a rate of 325 MeV/m. It is shown that for single-bunch injection, nearly the maximum energy gain can be attained within a temporal window of 0.5 fs. The obtained results provide a quantitative basis for optimizing DLA designs with triangular gratings, highlighting the significant role of the saw-tooth profile base angle and the grating type in achieving high rates for next-generation accelerators.
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All authors O.O. Svystunov, A.V. Vasyliev, I.V. Beznosenko, R.A. Melnichuk, G.V. Sotnikov
Accelerator Physics
Mutually phase-stable tunable attosecond soft X-ray attosecond pulses from a free-electron laser
River Robles, Kurtis Borne, Mathew Britton et al. (+16 more)
We demonstrate the production of mutually phase-stable attosecond X-ray pulse pairs with tunable relative time delays and phases in a cascaded X-ray free-electron
laser. We showcase the method in an experiment at the LCLS-II, in which a shaped electron beam is used in a split undulator configuration to generate the two attosecond pulses. We achieve mutual phase stability by reusing microbunching generated in the first undulator in order to seed the FEL process in the second at a detuned frequency. We measure controllable temporal delays between the two pulses directly in the time domain using angular streaking of photoelectrons, with a step size of 250 attoseconds. We then show that the behavior of the X-ray spectrum is consistent with phase stability between the two pulses, with a relative phase that can be easily tuned using inter-undulator phase shifters. This method is particularly well-suited to few to ten eV energy separations and sub to few femtosecond time delays, which are ideal for experiments in the soft X-ray regime for pushing the limits of our models for molecular dynamics and exerting direct coherent control over
quantum systems.
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All authors River Robles, Kurtis Borne, Mathew Britton, David Cesar, Paris Franz, Veronica Guo, Gabriel Just, Kirk A. Larsen, Randy Lemons, Vyacheslav Leshchenko, Xiang Li, Ming-Fu Lin, Razib Obaid, Nicholas Sudar, Jun Wang, Zhen Zhang, James Cryan, Taran Driver, Agostino Marinelli
Physics and Society
Emergence of cooperation: A reputation-modulated reinforcement learning
Chenyang Zhao, Jiqiang Zhang, Li Chen et al. (+1 more)
Reputation is widely recognized as a key mechanism for sustaining cooperation. However, most existing game-theoretic models treat reputation primarily as an external factor that modulates payoffs, interaction structures, or strategy update rules. In many social contexts, though, reputation operates primarily as information – it shapes how individuals interpret their own experiences and assess the behavior of others. To bridge this gap, we propose a spatial prisoner's dilemma game grounded in the reinforcement learning paradigm, in which
agents equipped with Q-learning integrate both individual and social information via a locally defined reputation metric to guide their decisions. Our results reveal that reputation-modulated learning significantly promotes the emergence of cooperative behavior, and we observe a discontinuous phase transition from full cooperation to full defection as the temptation increases. Cooperation spreads through the nucleation of cooperative clusters, whereas the disintegration of these clusters drives the system into an absorbing state of complete defection. Overall, this study demonstrates that reputation facilitates cooperation not only by providing direct incentives but also by reshaping the social information landscape that
agents rely on for learning and adaptation.
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All authors Chenyang Zhao, Jiqiang Zhang, Li Chen, Yong Zou