The complete learning of any unknown many-body systems requires a number of samples exponentially in the particle number. Several works consider subclasses of physical meaningful states such as stabilizer states or high-temperature Gibbs states that can be learned in polynomial sample complexity. Others consider to learn states under special assumptions, such as PAC learning and shadow tomography. In this work, we consider learning many-body systems that can be approximately represented by restricted Boltzmann machines (RBMs). We exhibit robustness results for efficient provable two-hop neighborhood learning method for ferromagnetic and locally consistent RBMs. We consider the $L_p$ norm as a distance measure, including both total variation distance and max-norm distance in the limit. We show that various quantum states can be learned with a sample complexity exponentially better than the naive state tomography. Our results establish a broader theoretical framework for the efficient learning of complex quantum many-body systems.

We investigate the impurity problem of a highly polarized Fermi gas with periodically modulated atom-atom interactions. We find that generalized time-periodic Floquet polaron and molecule emerge as quasistationary quasiparticle states of the system, which exhibit peculiar features distinct from those in a static system. Even in the high-frequency limit, the periodic driving can renormalize the scattering length of the static (effective) Hamiltonian and thus modify the polaron-to-molecule transition. Remarkably, due to the folding of the quasienergy of the Floquet states in the Floquet Brillouin zone, unusual energy-level crossings beyond the conventional polaron-to-molecule transition occur. In particular, when the driving frequency is in resonance with the quasienergy difference, both branches of the Floquet polaron can intersect with the molecular state or even themselves under weak driving. The unique physics of these Floquet impurity states is further characterized and elucidated by the experimentally measurable spectral functions and the radio-frequency spectra. Our results pave a way to explore the intriguing nonequililbrium impurity physics beyond a static system via “Floquet engineering.”

Controlling the size of droplets, for example, in biological cells, is challenging because large droplets typically outcompete smaller droplets due to surface tension. This coarsening is generally accelerated by hydrodynamic effects, but active chemical reactions can suppress it. We show that the interplay of these processes leads to three different dynamical regimes: (1) Advection dominates the coalescence of small droplets, (2) diffusion leads to Ostwald ripening for intermediate sizes, and (3) reactions finally suppress coarsening. Interestingly, a range of final droplet sizes is stable, of which one is selected depending on initial conditions. Our analysis demonstrates that hydrodynamic effects control initial droplet sizes, but they do not affect the later dynamics, in contrast to passive emulsions.

Variability of motility behavior in populations of microbiological agents is a ubiquitous phenomenon even in the case of genetically identical cells. Accordingly, passive objects introduced into such biological systems and driven by them will also exhibit heterogeneous motion patterns. Here, we study a biohybrid system of passive beads driven by active ameboid cells and use a likelihood approach to estimate the heterogeneity of the bead dynamics from their discretely sampled trajectories. We showcase how this approach can deal with information-scarce situations and provides natural uncertainty bounds for heterogeneity estimates. Using these advantages, we particularly uncover that the heterogeneity in the system is time-dependent.

Monoclinic bismuth vanadate ($\mathrm{m}\text{−}{\mathrm{BiVO}}_4$) is a promising indirect band gap semiconductor for photoelectrochemical water splitting, yet the characteristics of its low-lying photoexcitations, or excitons, remain poorly understood. Here, we use an ab initio Bethe-Salpeter equation approach that incorporates phonon screening to compute the nature and lifetimes of the low-lying excitons of $\mathrm{m}\text{−}{\mathrm{BiVO}}_4$. Our calculations indicate that at 0 K, the lowest-lying exciton energy exceeds the indirect band gap, enabling spontaneous dissociation into free carriers via phonon emission within picoseconds. At 300 K, both phonon emission and absorption effects reduce this timescale to only a few femtoseconds. Phonon screening also greatly reduces the binding energy of the lowest-lying exciton, leading to an optical absorption spectrum that better reproduces experimental measurements. Overall, our findings establish the general conditions under which phonon emission-driven exciton dissociation can occur in indirect gap semiconductors, and they emphasize the critical role phonon screening can play in predictive calculations of photophysical properties of complex materials.

Disorder can profoundly influence synchronization in networks of nonlinear oscillators, sometimes enhancing coherence through external tuning. In semiconductor lasers, however, achieving high-quality steady-state synchronization is desired, while intrinsic and typically uncontrollable disorder poses a major challenge. Under fixed frequency disorder, we investigate homogeneous fully coupled external-cavity semiconductor lasers governed by the complex, time-delayed Lang-Kobayashi equations with experimentally relevant parameters and identify an optimal coupling strength that maximizes steady-state synchronization in the weak-coupling regime, which we term disorder-mediated synchronization resonance. This optimum appears for any fixed configuration of intrinsic frequency detuning and scales inversely with the number of lasers, leading to a linear scaling of the total coupling cost with the number of lasers. A theory based on an effective thermodynamic potential explains this disorder-mediated optimization, revealing a general mechanism by which moderate coupling can overcome static heterogeneity in nonlinear physical systems.

Using a custom-built scanning system, we generated maps of birefringence on reflection at $\lambda =1064$ nm from single-crystal GaAs/${\mathrm{Al}}_{0.92}{\mathrm{Ga}}_{0.08}\mathrm{As}$ Bragg reflectors (henceforth “AlGaAs coatings”). Ten coatings were bonded to fused silica substrates and one remained on the epitaxial growth wafer. The average phase difference on reflection between beams polarized along the fast and slow axes of the coating was found to be $\psi =1.09\pm 0.18$ mrad, consistent with values observed in high-finesse optical reference cavities using similar AlGaAs coatings. Scans of substrate-transferred coatings with diameters between 18 and 194 mm showed birefringence nonuniformity at a median level of $0.1$ mrad. A similar epitaxial multilayer that was not substrate transferred, but remained on the growth wafer, had by far the least birefringence nonuniformity of all mirrors tested at $0.02$ mrad. On the other hand, the average birefringence of the epi-on-wafer coating and substrate-transferred coatings was indistinguishable. Excluding nonuniformity found at the location of crystal and bonding defects, we conclude that the observed nonuniformity was imparted during the substrate transfer process, likely during bonding. Quantifying the impact on the scatter loss in a LIGO (Laser Interferometer Gravitational wave Observatory) interferometer, we find that birefringence nonuniformity at the levels seen here is unlikely to have a significant impact on performance. Nonetheless, future efforts will focus on improved process control to minimize and ultimately eliminate the observed nonuniformity.

We investigate the information-theoretic power of spatial superposition by analyzing tasks in which information is locally encoded at multiple distant sites and must be acquired by a single information carrier, such as a particle. Within an operational framework, we systematically compare the statistical correlations that can be generated in such tasks using classical particles, quantum particles in spatial superposition, and more general “second-order interference” resources. We bound classical strategies via convex polytopes and present a study of their symmetry, demonstrating that the vertices are inherently connected to $K$-juntas as defined in the classical theory of Boolean functions, while their facet inequalities are in one-to-one correspondence with oracle games. We then analyze the violation of the “fingerprinting inequality” achievable by the use of one quantum particle, and we study the dependence of this violation on the dimension $d$ of the particle's internal degree of freedom. In particular, we show that the case of $d=2$ can achieve a higher violation of the inequality than the previously investigated case of $d=1$. We also provide analytic and numerical evidence that this violation cannot be further increased for larger $d>2$. Finally, we find that both quantum and any other (generalized) second-order interference models exhibit the same asymptotic scaling in violating the fingerprinting inequality. Our results thereby further articulate quantum interference and spatial superposition as a resource for information processing.

Compact, stable, and versatile laser-driven ion sources hold great promise for applications ranging from medicine to materials science and fundamental physics. While single-shot sources have demonstrated favorable beam properties, including the peak fluxes necessary for several applications, high-repetition-rate operation will be necessary to generate and sustain the high average flux needed for many of the most exciting applications of laser-driven ion sources. Further, to navigate through the high-dimensional space of laser and target parameters toward experimental optima, it is essential to develop ion acceleration platforms compatible with machine learning techniques and capable of autonomous real-time optimization. Here, we present a multi-Hz ion acceleration platform employing a liquid sheet jet target. We characterize the laser-plasma interaction and the laser-driven proton beam across a variety of key parameters governing the interaction using an extensive suite of online diagnostics. We also demonstrate real-time, closed-loop optimization of the ion beam maximum energy by tuning the laser wave front using a Bayesian optimization scheme. This approach increased the maximum proton energy by 11% compared to a manually optimized wave front by enhancing the energy concentration within the laser focal spot, demonstrating the potential for closed-loop optimization schemes to tune future ion accelerators for robust high-repetition-rate operation.

We report an optical dipole trap of strontium monohydroxide (SrOH) with 1400(300) trapped molecules. Through optical pumping, we access vibrational states that are proposed for improved probes of the electron’s electric dipole moment (eEDM) and ultralight dark matter (UDM). For each of these states, the lifetime of trapped molecules is measured and found to be consistent with spontaneous radiative decay and blackbody excitation limits, making this platform viable for these eEDM and UDM searches.

Satellite-based quantum repeaters are a promising means of reaching global distances in quantum networking due to the polynomial decrease of optical transmission with distance in free space, in contrast to the exponential decrease in optical fibers. We propose a satellite-based quantum repeater architecture with trapped individual atomic qubits, which can serve both as quantum memories and true single-photon sources. This hardware allows for nearly deterministic Bell measurements and exhibits long coherence times, without the need for costly cryogenic technology in space. We develop a detailed analytical model of the repeater, which includes the main imperfections of the quantum hardware and the optical link, assuming high-altitude ground stations, and consequently working in a regime of weak atmospheric turbulence. Our model allows us to estimate that high-rate and high-fidelity entanglement distribution can be achieved over intercontinental distances. In particular, we find that high-fidelity entanglement distribution over thousands of kilometres at a rate of 100 Hz can be achieved with orders of magnitude fewer memory modes than conventional architectures based on optical Bell state measurements.

Understanding how neurodegenerative diseases disrupt brain dynamics requires models capable of capturing the interplay between network structure and functional activity. This study presents a hardware emulation of progressive disconnection, implemented using a physical network of transistor-based chaotic electronic oscillators inspired by a biological neuronal culture. We evaluate several node disruption scenarios under different coupling strengths. These included single-node disruption and progressive damage sequences from core to periphery and periphery to core. The changes in network and node-level dynamics are assessed through the evaluation of synchronization, entropy, spectral content, and graph-theoretic properties. These analyses show that the network’s response to progressive alteration depends strongly on its topology and the coupling strength. The single-node disruption scenario revealed a high level of network resilience. Changes in average phase synchronization and topology remained modest in this scenario, consistent with functional imaging and lesion studies showing early compensatory mechanisms in healthy and mildly impaired brains. While the periphery-to-core scenario causes gradual and delayed deterioration, the core-to-periphery scenario leads to a sharp breakdown in synchronization, as well as structural and functional graph-based metrics. These profiles of degradation are comparable to those observed in neurodegenerative diseases and, in particular, Alzheimer’s disease, characterized by marked damage to central regions. Remarkably, it is found that modularity reaches a peak and then decreases just before the network collapses, a pattern that may be considered a meaningful marker of network degradation. Spectral analyses reveal a progressive shift toward low frequencies and fragmentation of the oscillatory dynamics, characterized by a decrease in high-frequency power and emergence of local frequency peaks. This study provides insights into how topology-dependent degeneration shapes brain rhythms and functional connectivity. It demonstrates that physical oscillator networks are suitable for emulating the progressive breakdown of neural circuits. The obtained insights could form the basis for hypothetical biomarkers.

We propose the parity flow formalism, a method for tracking the information flow in quantum circuits. This method adds labels to quantum circuit diagrams such that the action of Clifford gates can be understood as a recoding of quantum information. The action of non-Clifford gates in the encoded space can be directly deduced from those labels without backtracking. An application of flow tracking is to design resource-efficient quantum circuits by changing any present encoding via a simple set of rules. Finally, the parity flow formalism can be used in combination with stabilizer codes to further reduce quantum circuit depth and to reveal additional operations that can be implemented in parallel.

It is shown that a semiclassical Rabi model with parity-time $\left(\mathcal{PT}\right)$ symmetry possesses quasiexact solutions, which can be found using the Lie-algebraic approach. These solutions are located precisely at the exceptional points of the spectrum, the boundaries of the $\mathcal{PT}$-symmetric phase. The corresponding constraints on the model parameters can be interpreted as a resonance relationship between the constant and periodic driving terms. For sufficiently large resonance ratio and judiciously chosen parameters, we find that the time evolution of the complete qubit can be described exactly.

Polar polymer activity underlies numerous cellular processes driven by molecular motors or enzymes. Active polymers with activity on all constituent monomers display compact globular structure, while polymers with only head activity are known to result in stretched configurations. However, most biological and synthetic polymers feature activity localized in just a few sites, a scenario that significantly differs from both previous limits. In this work, we investigate how the density and distribution of motors critically influence the conformational and dynamical properties of polar active polymers. Using overdamped Langevin dynamics simulations, we show that globular conformations for high motor densities change to stretched ones for the more realistic moderate or low density of motors. Interestingly, the polymer's velocity exhibits a nonmonotonic dependence on motor density, with maximum propulsion at intermediate densities. Furthermore, the location of the first motor profoundly impacts polymer conformations; even a slight shift leads to drastic differences between coiled and stretched states. Our findings reveal that motor placement and density govern the structural transitions, characteristic timescales, and propulsion dynamics of polar active polymers, which will have numerous practical implications in the design and understanding of active synthetic and biopolymers.

Convergent-beam electron diffraction (CBED) is a well-established probe for spatial symmetries of crystalline samples, mainly exploiting the well-defined mapping between the diffraction groups (symmetry group of CBED patterns) and the point-group symmetries of the crystalline sample. In this work, we extend CBED to determine magnetic point groups. We construct all magnetic CBED groups, of which there exist 125. Then, we provide the complete mapping of the 122 magnetic point groups to corresponding magnetic CBED groups for all crystal orientations. In order to verify the group-theoretical considerations, we conduct electron-scattering simulations on antiferromagnetic crystals and provide guidelines for the experimental realization. Based on its feasibility using existing technology, as well as on its accuracy, high spatial resolution, and small required sample size, magnetic CBED promises to become a valuable alternative method for magnetic structure determination.

Muon-spin spectroscopy at continuous sources has stagnated at a stopped muon rate of $\sim 40\mathrm{kHz}$ for the last few decades. The major limiting factor is the requirement of a single muon in the sample during the typical $10\mu \mathrm{s}$ data gate window. To overcome this limit and to be able to perform muon-spin relaxation/rotation (µSR) measurements on millimeter-sized samples, one can use vertex reconstruction methods to construct µSR spectra. This is now possible thanks to the availability of very thin monolithic Si-pixel chips, which offer minimal particle scattering and high count rate. Here, we present results from a Si-pixel-based spectrometer that utilizes vertex reconstruction schemes for the incoming muons and emitted positrons. With this spectrometer, we were able to obtain a first vertex reconstructed ($\text{vx-}\mu \mathrm{SR}$) spectrum. The unique capabilities and benefits of such a vx-µSR spectrometer are discussed.

Recently, the driven dynamics of localization phase transition have garnered growing interest. However, studies so far have mainly considered initial localized states, whose driven dynamics follow the Kibble-Zurek mechanism (KZM). In this study, we investigate the driven dynamics of the localization phase transition in the Aubry-André model starting from a gapless extended state, which violates the adiabatic-impulse scenario of KZM. By linearly driving the quasiperiodic potential strength across the critical point, we numerically simulate the driven dynamics and analyze the scaling behavior of both the inverse participation ratio ($\mathcal{I}$) and the dynamic deviation from the instantaneous ground-state energy $\left(\mathcal{D}\right)$. We demonstrate that the driven dynamics starting from initially extended states satisfies the criterion for the applicability of KZM and its extension, finite-time scaling (FTS). The scaling functions governing the driven dynamics of both $\mathcal{I}$ and $\mathcal{D}$ have been derived based on FTS and numerically validated. We found that the scaling functions exhibit significant differences at large $R$ and small $R$, and also differ considerably from the scaling functions when the initial state is localized, highlighting the crucial role of initial-state behavior. The established scaling laws remain robust across a wide range of system sizes and driving rates, providing testable predictions for experimental realizations.

Electronic conduction at the atomic scale can be described by Landauer’s formalism. In single-atom point contacts of noble metals like Au and Ag, there is just one channel open between both electrodes and the conductance is very close to the quantum of conductance $G\approx G_0=\frac{2e^2}{h}$, with the factor of two coming from spin degeneracy. The magnetoconductivity of atomic size contacts has been studied for numerous systems, unveiling local Kondo screening, magnetic order, and spin-polarized currents. However, these have been mostly performed in elements with multiple open conduction channels where $G$ differs from $G_0$. The realization of a magnetically active conductor with a single-open channel remains difficult to achieve. Here, we present measurements of the electronic conductance of single-channel Au and Ag atomic size contacts in magnetic fields up to 20 T. We observe a decrease in $G$ which goes up to about 15% in many Au contacts at 20 T. We perform calculations and find that pure Ag and Au do not present a strong field dependence of $G$, in agreement with previous results at smaller magnetic fields. We also find, however, that residual ${\mathrm{O}}_2$ molecules attached close to the contact produce an induced spin-polarized current, which leads to a decrease in $G$. We discuss the role of the magnetic response of the electrodes in the jump-to-contact. Our results suggest that single channel atomic size conductors with a sizable response to a magnetic field can be built by combining noble metals and magnetically active molecular systems.