Non-neutral plasmas can be confined for long times in electromagnetic traps. Adiabatic cooling of such plasmas can be achieved by slowly decreasing the effective trap stiffness and letting the plasma occupy a larger volume. Here, we propose an optimal control strategy to cool an antiproton plasma in a time much shorter than that required by an adiabatic process. The optimal cooling protocol is found by minimizing an appropriate cost functional that measures the distance of the system from the desired “cold” state, while keeping the stiffness amplitude within prescribed limits. The proposed optimal protocol is shown to outperform other expansion-based cooling methods in terms of stability of the plasma, duration of the process, and volume occupied by the final plasma.

Lacking a universal law for granular flows across gravitational environments, fundamental processes such as hopper discharge remain vulnerable to failure in low gravity environments. A central challenge is clogging, the spontaneous arrest of flow through a constriction; yet previous studies report contradictory results on its dependence on gravitational acceleration. We identify the granular Bond number as the missing control parameter, defined as the ratio of intrinsic cohesive interactions among particles to gravity. Based on an in-bulk measurement of this quantity, we propose to rescale Earth-measured data for predicting granular behavior in low gravity. We present experiments of granular flow through an orifice under true reduced gravity (Moon and Mars), using an active drop tower, and extraterrestrial soil simulants as model cohesive materials. Our experiments reveal substantial increases in clogging probability, contrary to previously predictions, which depends on the properties of the material itself. When rescaled by the Bond number, seemingly conflicting results can be explained and collapse into a unified state diagram, predicting clogging across materials and gravitational accelerations. This establishes a general framework for the cohesion-to-gravity competition. Future space missions to the Moon, Mars, and asteroids will rely on such predictions of granular behavior in low gravity.

We employ a variational neural annealing approach for solving large-scale constrained portfolio optimization problems, mapped onto classical Ising-like Hamiltonians, and study its performance under finite annealing times. The method enables efficient exploration of high-dimensional feasible spaces and achieves competitive solutions on standard financial indices. To characterize the underlying optimization dynamics, we analyze the decay of the residual energy as a function of annealing steps and observe a power-law behavior for fixed problem size. Extending this analysis across different portfolio sizes, we examine whether the optimization dynamics are consistent with a dynamical finite-size scaling form and find that the residual energy data collapse onto a single scaling curve within the studied range. This scaling analysis yields an effective annealing-time exponent that quantifies how computational effort grows with problem size. Our results demonstrate that finite-size scaling concepts provide a useful framework for understanding and forecasting the performance of neural annealing-based optimization methods in realistic, constrained settings.

Suspensions of paramagnetic colloids exhibit kinetic arrest in strong magnetic fields. Through a dissipative process of toggling the field on and off, suspensions self-assemble into dense and dynamic steady-state phases. We construct a phase diagram using $k$-means clustering analysis based on domain elongation, α-shapes, contour metrics, and the degree of phase separation. We identify six characteristic structural regimes: a structureless phase, an arrested structure, sheets, ribbons, a spiky phase, and a transient fluid-fluid regime. We further report the distribution and alignment of domains and the generality of the results. We model self-assembled domain shapes using an equilibrium mean-field magnetostatic energy calculation, which predicts the surprising emergence of highly anisotropic structures driven by the sample's confinement.

The ability to optimize the properties of a material is particularly advantageous for applications. Here the tuneable properties of side-chain liquid crystal elastomers (LCEs) are investigated. LCEs were fabricated using the same acrylate monomers, varying the proportion of mesogenic groups to influence the phase, density, and mechanical properties. The density increases with mesogenic content, varying from $1.11\mathrm{g}/\mathrm{c}{\mathrm{m}}^3$ to $1.19\mathrm{g}/\mathrm{c}{\mathrm{m}}^3$ as the mesogenic content is increased from 51 mol% to 99 mol%. The 7% increase in density was attributed to closer packing of the nanoscale network, observed directly through Small- and Wide-Angle X-ray Scattering. A 22% reduction in the network end-to-end spacing was measured for LCEs as the mesogenic content was changed from 56 mol% to 75 mol%. LCEs with above 70 mol% mesogenic content were revealed to exhibit a frustrated smectic phase, with nematic phases confirmed for the lower mesogenic concentrations. The frustrated smectic materials exhibit a higher correlation length parallel to the director ($>125\AA$) than the nematic LCEs ($<100\AA$) and demonstrate significantly higher Young's moduli, with the greatest moduli perpendicular to the director measured at $21{}^{\circ }\mathrm{C}$ as 8.3 MPa for the smectic LCEs and as a constant value of 2.1 MPa for the nematic LCEs. Crucially, this demonstrates that only a small change in the mesogenic content can induce a transition from a nematic LCE to a frustrated smectic LCE. This series of materials reveals how the nanoscale packing, the macroscopic material properties, and the phase can be controlled via the mesogenic content in side-chain acrylate LCEs, suggesting design approaches that allow for the potential customization of the material properties for applications.

Neuromodulatory levels in the brain change moment to moment, yet are typically ignored in studies of neural criticality, where empirical support remains varied. Here we show in a biophysical network of bursting neurons that arousal acts as a mechanistic control parameter for a directed percolation phase transition. At intermediate arousal, neuronal activity exhibits peaked susceptibility, power-law avalanche size and duration distributions, universal shape collapse, and anomalous diffusion, jointly satisfying the hyperscaling relation of the 2+1-dimensional directed percolation universality class. Reanalyzing extracellular recordings in awake mice, we find that time-resolved susceptibility tracks pupil-inferred arousal as the model predicts. These results identify arousal as a physiological control parameter for neural criticality, offering a statistical-physics basis for the Yerkes-Dodson effect, and imply that arousal should be tracked at fine temporal resolution to obtain reliable empirical estimates of neural criticality.

Numerical implementation of a theory yields acoustic wave packets whose peak-to-peak speeds from source to receiver are supersonic in a dispersionless medium due to temporal interference between direct and boundary-reflected paths. The effect occurs when the source and receiver are near each other and at least one is within $c\widetilde{\delta t}/2$ of the boundary, where $c$ is the phase speed of propagation in the medium, and $\widetilde{\delta t}$ is the smallest temporal separation between the paths at which interference first occurs. This $\mathrm{direct}+\mathrm{reflected}$ path mechanism is distinct from mechanisms yielding superluminal speeds for electromagnetic waves (EM) including quantum tunneling and anomalous dispersion. For temporally interfering $\mathrm{direct}+\mathrm{reflected}$ acoustic paths, simulations yield a speed of information less than $c$. The speed of information from the interfering paths can exceed the speed derived from propagation only along the direct path. We conjecture these results will also hold for EM waves. If so, we prove the speed of information is less than or equal to the speed of light in a vacuum, so the effect does not violate special relativity. These theoretical and simulation results, as well as their conjectured EM extension, should be readily accessible to experimental verification.

Granular gases are commonly characterized through their velocity distribution, which provides access to the granular temperature. In experiments, velocity distributions are typically obtained by particle tracking, which becomes, however, limited at moderate and high particle densities. As a way forward, we propose a new technique for measuring particle velocities in situ by using a fiber Bragg grating (FBG) sensor, which remains applicable at significantly higher particle densities. The FBG sensor detects strain pulses induced by particle-fiber collisions, from which the velocity of the impacting particle can be derived. Applying this method to an ensemble of granular particles allows us to extract its velocity distributions, as we present for a granular system excited by a vibrational shaker. We validate the extracted velocity distribution against conventional particle-tracking measurements, confirming the reliability of the FBG-based technique.

We demonstrate that the thermodynamic friction metric governing dissipation in slowly driven continuous-time Markov chains is equivalent to the commute-time embedding and the resistance distance. This equivalence yields complementary insights: The commute-time embedding demonstrates the intrinsic cost of transporting probability across dynamical bottlenecks, while the resistance distance maps thermodynamic dissipation to Joule heating in an electrical network. We further demonstrate that the linear-response thermodynamic distance is a discrete $L^2$-Wasserstein optimal transport cost evaluated along paths of equilibrium distributions, extending a continuous-state correspondence to discrete networks. This conceptual synthesis of linear-response thermodynamics, random walks on graphs, electrical circuits, and optimal-transport theory connects independently developed geometric frameworks, reduces complex metric calculations to simple circuit algebra, and provides a clear physical picture of dissipation as the energetic cost of routing probability through the state space network.

The achievement of fusion ignition at the National Ignition Facility opens new opportunities for foundational studies in opacity, radiation transport, and high-flux astrophysics in regimes previously unattainable. We have succeeded in the critical enabling step of demonstrating ignition in a hohlraum modified with diagnostic windows that burn through prior to ignition, granting experimental access to the brightest radiation source in the laboratory. This Letter reports the results of a deuterium-tritium-layered capsule implosion that achieved $2.4\pm 0.09$ MJ neutron yield in a hohlraum with windows designed to allow the escape of radiation energy from the capsule without significant loss of implosion symmetry, thus establishing a validated platform for next-generation radiation-driven experiments.

Stochastic dynamical systems allow modeling of transitions induced by random disturbances, in particular from an attracting equilibrium and crossing the stable manifold of a saddle. While the small-noise limit is well-described by the large deviation principle, existing computational methods often struggle with stochastic forcings any more complicated than nondegenerate Gaussian white noise, and with unbounded time intervals. The primary innovations of this work are extending the framework to cater for colored and degenerate forcing and unbounded time horizons—scenarios that are physically realistic but numerically challenging. We cater for degenerate noise by using the Hamiltonian optimal control method. We cater for a class of colored noises by using linear filters on white noise. We cater for infinite time horizon by introducing the method of division (MOD), a computational approach for approximating rare transition events, including their most likely paths and the exponential scaling laws of their transition rates. The effectiveness of MOD and the above approaches to colored noise, is demonstrated by illustration on two examples: an inverted double-well potential and a simplified roll-heave model for ship capsize.

We present an explicit construction of the Freidlin-Wentzell quasipotential of a stochastic system with two degrees of freedom and nonreciprocal interactions. This model undergoes noise-induced transitions between four metastable attractors, forming recurrent but aperiodic “Escher cycles,” similar to the cyclic nucleation dynamics observed in the nonreciprocal Ising model. We calculate the quasipotential analytically to first order in nonreciprocality. We characterize it along a one-dimensional reaction coordinate that connects the attractors, and we also obtain the full two-dimensional landscape, at leading order in perturbation theory. The resulting landscapes feature flat regions and extended plateaus, together with nondifferentiable switching lines. These singular structures arise from two geometric mechanisms: the handover of dominance between competing transition paths, and the competition between basins of attraction. The system provides a rare case where the geometry of nonequilibrium rare events can be fully resolved, and a simple analytically tractable example of a quasipotential in more than one coordinate that captures a rich set of nonequilibrium features.

Quasimonoenergetic proton beams have long been anticipated in laser-driven ion acceleration, particularly via multispecies targets in radiation pressure and target normal sheath acceleration, yet experimental results are far from expectations, and the underlying cause remains elusive. Here we reveal that even under ideal conditions, only a power-law energy spectrum $d{\mathcal{N}}_p/d{\mathcal{E}}_p\propto {\mathcal{E}}_p^{-\eta }$, rather than a quasimonoenergetic one, is predicted by theory when full spatial dynamics are considered, where ${\mathcal{N}}_p$, ${\mathcal{E}}_p$, and $\eta$ represent the proton number, energy, and power-law index, respectively. Our theory and three-dimensional particle-in-cell simulations demonstrate that the spectral shape and index $\eta$ are independent of the specific acceleration mechanism, but are correlated with the target composition and laser focal spot profile. This provides a plausible explanation for the power-law spectra observed in experiments across a wide range of laser and plasma parameters. Possible paths to breaking the universality and achieving quasimonoenergetic proton beams are discussed.

Polymer mixtures fractionate between phases depending on their molecular weight. Consequently, by varying solvent conditions, a polydisperse polymer sample can be separated between phases to achieve a particular molecular weight distribution in each phase. In principle, predictive physics-based theories can help guide separation design and interpret experimental phase-diagram and fractionation measurements. Even so, applying the standard Flory-Huggins model can require numerical computations that hamper the predictions considering the full molecular weight distribution. Here, we apply a recently derived exact analytical solution of multicomponent Flory-Huggins theory for polydisperse homopolymers to understand the principles of polymer fractionation for common molecular weight distributions. Consistent with previous studies, the method highlights the sensitivity of polymer fractionation to the shape, and in particular the tails, of this distribution. Our results provide a systematic approach to evaluate the full molecular weight distribution in phase coexistence calculations over the possible composition space.

During gas breakdown between two parallel-plate electrodes excited by radio frequency (RF), a time-dependent striated optical emission structure is experimentally observed. Its formation process is reproduced and explained using particle-based simulations. The striations appear due to significantly different mobilities of ions and electrons, which lead to the formation of space charge in the vicinity of the extrema in the charged-particle densities under a strong RF electric field. The striated structures of the charge density as well as other parameters are amplified by locally enhanced ionization rates associated with the growing charged-particle density, and are eventually suppressed as the RF electric field is progressively screened from the discharge central region.

We derive the exact nonequilibrium steady state of a run-and-tumble particle (RTP) in $d$ dimensions confined in an isotropic harmonic trap $V\left(\mathbf{r}\right)=\mu r^2/2$, with $r=\parallel \mathbf{r}\parallel$. Rotational invariance reduces the problem to the stationary single-coordinate marginal $p_X\left(x\right)$, from which the radial distribution $p_R\left(r\right)$ and the full joint stationary density follow by explicit integral transforms. We first focus on a generalized trapped RTP in one dimension, where post-tumble velocities are drawn from an arbitrary distribution $W\left(v\right)$. Using a Kesten-type recursion, we represent its stationary position in terms of a stick-breaking (or Dirichlet) process, yielding closed-form expressions for its distribution and its moments. Specializing $W\left(v\right)$ to the projected velocity law of an isotropic RTP, we reconstruct $p_R\left(r\right)$ and the full joint distribution of all the coordinates in $d=1,2,3$. In $d=1$ and $d=2$, the radial law simplifies to a beta distribution, while in $d=3$, we derive closed-form expressions for $p_R\left(r\right)$ and the stationary joint distribution $P(x,y,z)$, which differ from a beta distribution. In all cases, we characterize a persistence-controlled shape transition at the turning surface $r=v_0/\mu$, where $v_0$ is the self-propulsion speed. We further include thermal noise characterized by a diffusion coefficient $D>0$, showing that the stationary law is a Gaussian convolution of the $D=0$ result, which regularizes turning-point singularities and controls the crossover between persistence- and diffusion-dominated regimes as $D\to 0$ and $D\to \infty$, respectively. All analytical predictions are systematically validated against numerical simulations.

We discuss the order statistics of the particle positions of a gas of $N$ identical independent particles performing Brownian motion in one dimension in a potential that asymptotically behaves like $V\left(x\right)\sim x^{\gamma }$ for $x\to +\infty$, with a positive power $\gamma >0$. We show that in the stationary state, the order statistics that describe how the leaders are reshuffled are universal and independent of $\gamma$. What depends on $\gamma$ is the timescale of the leaders' reshuffling, which scales as a power of the logarithm of the population size: $t\sim {(lnN)}^{\frac{2(1-\gamma )}{\gamma }}\tau$, where $\tau$ is of order one. We derive the probability that the particle which has the $k$-th largest value of $x$ at some time $t_1$ will have the $j$-th largest value at time $t_2=t_1+t$ in the form of an explicit expression for the generating function for the reshuffling probabilities for all $k\ge 1$ and $j\ge 1$. The generating function, expressed in scaled time $\tau$, is independent of $\gamma$. In particular, we show that the average percentage overlap coefficient of leader lists takes the universal, $\gamma$-independent form $\mathrm{erfc}\left(\sqrt{\tau }\right)$ for long lists.

How should one define thermodynamic quantities (internal energy, work, heat, etc.) for quantum systems coupled to their environments strongly? We examine three definitions, inspired by the literature, of a quantum system's internal energy under strong-coupling conditions. Each internal-energy definition implies a definition of work and a definition of heat. Our study focuses on quenches, common processes in which the Hamiltonian changes abruptly. In these processes, the first law of thermodynamics holds for each set of definitions by construction. However, we prove that only two sets obey the second law. We illustrate our findings using a simple spin model. Our results guide studies of thermodynamic quantities in strongly coupled quantum systems.

The fast-ignition paradigm for inertial confinement fusion allows for extremely high gains but requires fuel to be heated very quickly to outpace hotspot disassembly and energy losses. This demands lasers with high power and intensity, posing engineering challenges that have called into question the fundamental practicality of fast ignition. Magnetized liner inertial fusion (MagLIF) circumvents these problems through its large-aspect-ratio cylindrical geometry and strong axial magnetic fields that allow for ignition at lower areal densities. Furthermore, MagLIF's large aspect ratio and higher yields relax other constraints on energy deposition and repetition rate, while its axial magnetic fields can be used to collimate ignitor electrons and thereby increase allowed standoff distance and save on ignitor energy. This tremendous overall relaxation of the engineering constraints that have historically limited the practicality of fast ignition suggests that the paradigm may be considerably more viable in a MagLIF context.

Understanding the atomic-scale dynamics of liquids in the terahertz (THz) regime remains challenging because liquids sustain phonon-like collective excitations governed by complex interactions. To clarify the role of hydrogen bonding in such dynamics, we performed inelastic neutron scattering on hydrogen sulfide $\left({\mathrm{H}}_2\mathrm{S}\right)$ and its deuterated form $\left({\mathrm{D}}_2\mathrm{S}\right)$, molecular analogues of water without a hydrogen-bonded network. By combining coherent and incoherent measurements, we show that liquid ${\mathrm{H}}_2\mathrm{S}$ exhibits a clear fast-sound mode, with a propagation velocity about twice the adiabatic sound speed, as in water. In contrast to hydrogen-bonded liquids, which display a secondary, nearly momentum-independent mode at 6–7 meV, no corresponding feature is observed in liquid ${\mathrm{D}}_2\mathrm{S}$. This absence highlights the central role of hydrogen bonding in enabling additional low-energy excitations. Overall, while fast sound is not exclusive to hydrogen-bonded systems, the detailed vibrational spectrum is strongly shaped by the local bonding environment.