Turbulence transition often arises from a subcritical transition between bistable states characterized by invariant sets of deterministic dynamical systems, and such transitions can be triggered by system noise as rare events. In this study, we employ the Onsager-Machlup (OM) formulation of stochastic dynamics to examine the Hamilton equations governing the most probable transition paths (MPPs). We introduce an effective potential function, termed the OM potential, which depends on the noise intensity. Focusing on the Dauchot-Manneville model as a minimal system with an edge state, we comprehensively analyze the MPP for different transition times between two attracting points corresponding to laminar and turbulent states. We find that the MPPs cross the separatrix at nearly the same point regardless of the transition time, and the obtained OM action values suggest that the transition to turbulence occurs more frequently than the transition to the laminar state. Moreover, we numerically demonstrate that the noise-induced transition paths follow the OM potential landscape and its bifurcation diagram, indicating that the qualitative behavior of the MPPs is determined by the OM potential. Our methodology formulated in general dynamical systems provides a theoretical basis for predicting noise-induced transitions among invariant sets of the dynamics.

The optical generation of an out-of-equilibrium spin population is a keystone process for quantum technologies and spintronics alike. Although this is an established technique for studying direct band-gap semiconductors, it has been proven limited in materials that possess weak oscillator strengths for the optical transitions. We address the problem by presenting an all-optical analog of the spin-pumping method. By applying this concept to a Ge-on-Si heterostructure, we observe luminescence from Si with a polarization degree as high as 9%. The progressive etching of the absorbing layer, assisted by magneto-optic experiments, allows us to ascertain that the polarized emission is determined by effective spin injection aided by the carrier lifetime shortening due to extended defects. These findings can facilitate the use of highly promising spin-dependent phenomena of Si, whose optical exploitation has been hampered by fundamental limitations due to its peculiar electronic structure.

We present a data-efficient framework for constructing general classical spin Hamiltonians by combining the spin-cluster expansion (SCE) with fully self-consistent noncollinear spin density functional theory (DFT). The key idea is to fit the SCE model to magnetic torques rather than to total energies. Because torques are site-resolved vectors, each spin configuration provides many informative regression targets, improving conditioning and substantially reducing the number of required DFT calculations, especially for large supercells. Applied to the B20-type chiral magnets ${\mathrm{Mn}}_{1-x}{\mathrm{Fe}}_x\mathrm{Ge}$ and ${\mathrm{Fe}}_{1-y}{\mathrm{Co}}_y\mathrm{Ge}$, the resulting SCE models determine full pairwise exchange tensors—including isotropic exchange, symmetric anisotropic exchange, and the Dzyaloshinskii-Moriya interaction—and predict the helical spin period via a micromagnetic mapping. The composition trends and the divergence of the period at the chirality sign-change point are well reproduced, in agreement with experiment. Moreover, the systematic nature of SCE enables controlled assessment of interaction order: As the training spin configurations become more disordered, the lowest-order model loses torque accuracy, whereas including higher-order interactions restores predictive power. These advances enable near-DFT-accurate spin models for finite-temperature magnetism and complex spin textures at modest computational cost, providing an extensible route to quantitative first-principles parametrization and predictive materials design.

Photonic circuits modulated in time can convert the input light frequency ${\omega }_0$, shifting it by multiples of the modulation frequency ${\omega }_p$ and, in certain cases, amplify the total input light power. Of special interest are photonic circuits employing microwave capacitors, which instantaneously modulate photonic waveguides with frequency ${\omega }_p\ll {\omega }_0$. While the amplification of light is negligible in such circuits, ideally, frequency conversion can be completed with the conservation of the light amplitude. Therefore, similar to the elastically transparent photonic structures (i.e., structures conserving both the light amplitude and frequency), we can say that a photonic circuit parametrically modulated in time exhibits complete inelastic transparency if a wave enters the structure with frequency ${\omega }_0$ and exits it with a different frequency and the same amplitude. Here, we develop an approach that allows us to introduce and investigate a broad class of time-modulated photonic circuits exhibiting complete inelastic transparency. Light enters these circuits with a resonant frequency ${\omega }_0$, cascades between their N eigenstates separated by the modulation frequency ${\omega }_p$, and exits with frequency ${\omega }_0+\left(N-1\right){\omega }_p$ and the output amplitude close to the input amplitude. As examples, we consider circuits of ring microresonators and surface nanoscale axial photonics (SNAP) microresonators.

Linear polarization analysis of hard x-rays is employed to probe electronic anisotropies in metal-containing complexes with high selectivity. We use polarization-resolved nuclear forward scattering (PR-NFS) of synchrotron radiation at the 14.4 keV nuclear resonance of ${}^{57}\mathrm{Fe}$ to determine electric field gradients (EFGs) in an iron(II) spin-crossover compound as they evolve during a temperature-dependent high-spin/low-spin transition. A pair of crossed Si(840) channel-cut crystals provides a high-purity x-ray polarimeter that suppresses the nonresonant background by nearly nine orders of magnitude and enables selective detection of nuclear resonant $\sigma \to \pi$ scattering. Using the spin-crossover complex ${\text{Fe(PM-BiA)}}_2{\left(\text{NCS}\right)}_2$ as a model system, we determine the orientation of the EFG tensor in the high-spin and low-spin states and follow its reorientation across the gradual thermally driven spin transition. By choosing suitable sample orientations, the polarization selectivity enhances the signal of a high-spin minority fraction of a few percent at low temperature. It reveals that the high-spin EFG at 120 K is not randomly distributed and does not align with the dominant low-spin EFG when these high-spin centers form a minority phase embedded in a low-spin matrix. The combination of PR-NFS with dynamical NFS simulations and density-functional calculations thus provides a sensitive, element- and site-selective method to quantify electronic anisotropies and their changes across phase transitions in Mössbauer-active metal compounds.

Heating a long-range ordered adsorbate phase beyond its stability temperature does not necessarily result in a disordered phase; it can also break up into heavily fluctuating ordered domains. Temporal and/or spatial averaging over these fluctuations may give the impression of both a wrong periodicity and false symmetry elements such as nonexisting glide planes or rotational axes of incorrect order. This can happen in real space and reciprocal space, and also below liquid-nitrogen temperature, so that the true nature of the phase might remain undetected. We demonstrate this scenario at the catalytically active Rh(100) surface covered by $\frac{1}{2}$ monolayer of oxygen, using quantitative low-energy electron diffraction, variable-temperature scanning tunneling microscopy, and density functional theory. Using the example of CO adsorption, we show that local symmetry can have a decisive influence on the binding energy and thus the chemical reactivity.

Indefinite causal order (ICO) has the potential to be a new resource for quantum information processing. In most of its experiments, ICO has been investigated in a photonic platform. Here, we investigate ICO in a cavity quantum electrodynamics system composed of two cavities. Our results show that ICO can create highly entangled states of two distant cavity fields that never interact directly independent of the initial (excited or ground) state of the atom. These entangled states can have the form of one- or two-photon NOON states. We show that ICO can interchange one photon between both cavities without changing the state of the atom, something that is impossible to achieve for two cavities in well-defined order. Furthermore, the vacuum Rabi oscillations either disappear or lose their sinusoidal form with ICO. Our results show the potential that ICO can offer in the paradigm of light-matter interaction for coherently controlling atom-field observables.

The unicellular microalga Chlamydomonas reinhardtii (CR) is well known for its biflagellated swimming in response to light stimuli. This work aims to study the resynchronization of CR flagella after a high light intensity stimulus, known as photoshock. The synchronization is estimated thanks to a quantity defined as the phase synchronization index (PSI). The originality of this approach is to perform a time-frequency computation of a complex PSI based on continuous wavelet transform. Thanks to this analysis, we distinguish three swimming stages involving different frequency bands and phase shifts: synchronized breaststroke swimming, undulatory backward swimming, and resynchronization. This approach also reveals the presence of signal harmonics that set the photoshock response, independently of cell variability. Our results suggest that CR modulates the balance between spectral beating modes, providing a mechanism for robust adaptation to sudden environmental stresses.

Breaking Kirchhoff's law of thermal radiation yields opportunities in one-way radiative thermal transport and circuitry. We investigate its consequences in the far-field regime in cylindrical cavities, by employing a specular ray-tracing algorithm. At thermal equilibrium, we show that violation of Kirchhoff's law yields nonvanishing heat rectification coefficients within different sections of the cavity, which can be tuned for perfect rectification and circulation, while internal monochromatic currents vanish due to the intrinsic coupling between emission and absorption at specular surfaces. This constraint is lifted under nonequilibrium conditions, where rotational heat fluxes within the cavity can be precisely controlled by appropriately combining reciprocal and nonreciprocal materials. These findings open avenues for thermal management and provide design principles for nonreciprocal photonic devices.

We propose a decomposition of information flow into housekeeping and excess components for autonomous bipartite systems described by Markov jump processes. We introduce this decomposition using the geometric structure of probability currents and the conjugate thermodynamic forces. The housekeeping component arises from cyclic modes caused by violations of detailed balance and maintains the correlations between the two subsystems. In contrast, the excess component arises from conservative forces and alters the mutual information between the two subsystems. With this decomposition, we generalize previous results, such as the second law of information thermodynamics, the cyclic decomposition, and the information-thermodynamic extensions of thermodynamic trade-off relations.

Information geometry is a mathematical framework that elucidates the manifold structure of the probability distribution space (p space), providing a systematic approach to transforming probability distributions (PDs). In this study, we utilized information geometry to address the inverse problems associated with reconstructing PDs from experimental data. Our initial finding is that the Kullback-Leibler divergence, often considered nonmetric owing to its asymmetry, can serve as a valid metric under specific geometric conditions on the manifold. Based on this finding, we formulated the manifold-based gradient descent (MBGD) method, which was employed to visualize the internal structures—represented as PDs—of two types of systems: those with static constituent elements and those with dynamic state transitions. Through the application of MBGD, we successfully reconstructed the underlying PDs for both types of systems, outperforming the standard gradient descent methods that neglect the manifold structure of p space. Therefore, the present results demonstrate the essentiality of accounting for the manifold structure of p space in the inverse problems of reconstructing PDs. The ability of MBGD to accurately reconstruct PDs for systems with dynamic state transitions underscores its potential to provide valuable physical insights by visualizing internal structures.

We address the question of the implementation of long-distance device-independent quantum key distribution (DI QKD) by proposing two experimentally viable schemes. Those schemes use only spontaneous parametric down-conversion sources and linear optics. They achieve favorable key rate scaling proportional to the square root of channel transmittance ${\eta }_t$, matching the twin-field protocol advantage. We demonstrate positive asymptotic key rates at detector efficiencies as low as 80%, bringing DI QKD within the reach of current superconducting detector technology. Our security analysis employs the entropy accumulation theorem to establish rigorous finite-size bounds, achieving finite-key rates at a detector efficiency of 90%. This work represents a critical milestone toward device-independent security in quantum communication networks, providing experimentalists with practical implementation pathways while maintaining the strongest possible security guarantees against quantum adversaries.

Life relies on a sophisticated metabolic molecular machinery that turns over high-energy molecules to evolve complex macromolecules and assemblies. At the molecular origin of life, such machinery was absent, implying the need for simple yet robust physical mechanisms to harvest energy from the environment and perform chemical work or produce chemical power. However, the mechanisms involved in harvesting energy from a macroscopic cyclic environment to drive chemical processes on the molecular scale remain elusive. In this work, we propose a theory that describes the kinetics of chemical reactions in a system subject to a cyclic reservoir with varying properties. We compare cycles of solvent (wet-dry cycles), with cycles of a component participating in a chemical reaction (reactant cycle). We find that for both wet-dry and reactant cycles, resonance frequencies exist at which the chemical power is maximal. We identify which cycle type is more beneficial in harvesting chemical power for different molecular interactions. Our findings of harvest efficiencies around 10% suggest that the cyclic environment could have played a key role in catalyzing the metabolic molecular machinery at the molecular origin of life.

We analyze bipartite photon states in coincidence Compton polarimetry at energies where polarization must be inferred from Compton scattering. Polarization symmetry, defined as equality of signal and idler degree-of-polarization responses for all scattering angles, holds if and only if the initial two-photon state is pure and Bell equivalent. This identifies polarization symmetry as a state-level invariant that uniquely witnesses Bell-orbit structure under coincidence Compton scattering.

We report the formation of high-velocity microjets driven by the interference of two laser-induced shock waves in a tin microdroplet. A first 0.4-ns laser pulse launches a shock wave into the droplet (diameter $D_0=40$, 50, and $60\mu \mathrm{m}$). Due to the droplet's spherical geometry, the shock converges and diverges as it traverses the droplet center and reaches the back surface. Upon reflection from the free back surface, the shock reverses polarity, producing an intense, focused tensile wave. This wave nucleates an $\sim 1\mu \mathrm{m}$ cavitation bubble, trapping itself on the front side of the droplet, between the bubble and the droplet's free laser-facing surface. Impact of a second, delayed, identical laser pulse introduces a second shock wave and leads to the formation of a microjet. Scanning the delay of this second pulse reveals a complex pattern of constructive and destructive interferences of the two shocks through the observed change in jet velocity, with velocities reaching 110 m/s. This laser-droplet system presents a unique case for the study of acoustics and cavitation at the microscale.

A PLASEN (Precision LAser Spectroscopy for Exotic Nuclei) system, consisting of a compact radio-frequency quadrupole cooler buncher (RFQ-cb) and a collinear resonance ionization spectroscopy setup, has now been fully commissioned with radioactive ion beams at the Beijing Radioactive Ion-beam Facility (BRIF). Using both stable and radioactive Rb ion beams from BRIF, we demonstrated that the large beam energy spread observed at BRIF has been successfully handled by employing the RFQ-cb, enabling the delivery of high-quality bunched radioactive ion beams for collinear resonance ionization spectroscopy experiments. Under these conditions, we performed laser spectroscopy of exotic nuclei, achieving high resolution ($\sim 100\mathrm{MHz}$ spectral linewidth) and high sensitivity ($\sim 1:200$ efficiency). This fully operational PLASEN system will serve as a state-of-the-art experimental platform at BRIF for research in multiple fields such as nuclear, atomic, and molecular physics.

We introduce the notion of polynomial-depth duality transformations, which relates two sets of operator algebras through a conjugation by a poly-depth quantum circuit, and make use of this to construct efficient Gibbs samplers for a variety of interesting quantum Hamiltonians as they are poly-depth dual to classical Hamiltonians. This is, for example, the case for the two-dimensional toric code, which is demonstrated to be poly-depth dual to two decoupled classical Ising spin chains for any system size, and we give evidence that such dualities hold for a wide class of stabilizer Hamiltonians. Additionally, we extend the above notion of duality to Lindbladians in order to show that mixing times and other quantities such as the spectral gap or the modified logarithmic Sobolev inequality are preserved under duality.