Magnetic confinement fusion reactors produce fusion byproduct particles that must be removed for efficient operation. It is suggested to use autoresonance (a continuous phase locking between anharmonic motion and a chirped drive) to remove the fusion products from a magnetic mirror, the simplest magnetic confinement configuration. An analogy to the driven pendulum is established via the guiding center approximation. The full 3D dynamics is simulated for $\alpha$ particles [the products of deuterium-tritium (DT) fusion] in agreement with the approximated 1D model. Monte Carlo simulations sampling the phase space of initial conditions are used to quantify the method’s efficiency. The DT fuel particles are out of the bandwidth of the chirped drive and, therefore, stay in the mirror for ongoing fusion. The method is also applicable for advanced aneutronic reactors, such as $\mathrm{p}\text{−}{}^{11}\mathrm{B}$.

Despite the ubiquity of aqueous electrolytes, the effect of salt on water organization remains controversial. We introduce a nonlocal and nonlinear field theory for the nanoscale polarization of ions and water and derive the electrolyte dielectric response as a function of salt concentration to first order in a loop expansion. By comparison with molecular dynamics simulations, we show that rising salt concentration induces a dielectric permittivity decrement and Debye screening in the longitudinal susceptibility but leaves the water structure remarkably unchanged.

Understanding the mixing of open quantum systems is a fundamental problem in physics and quantum information science. Existing approaches for estimating the mixing time often rely on the spectral gap estimation of the Lindbladian generator, which can be challenging to obtain in practice. We propose a novel theoretical framework to estimate the mixing time of open quantum systems that treats the Hamiltonian and dissipative part separately, thus circumventing the need for a priori estimation of the spectral gap of the full Lindbladian generator. This framework yields mixing time estimates for a class of quantum systems that are otherwise hard to analyze, even though it does not apply to arbitrary Lindbladians. The technique is based on the construction of an energy functional inspired by the hypocoercivity of (classical) kinetic theory.

The NEWS-G direct detection experiment uses spherical proportional counters to search for light dark matter candidates. New results from a 10 day physics run with a 135 cm in diameter spherical proportional counter at the Laboratoire Souterrain de Modane are reported. The target consists of 114 g of methane, providing sensitivity to dark matter spin-dependent coupling to protons. New constraints are presented in the mass range 0.17 to $1.2\mathrm{GeV}/{\mathrm{c}}^2$, with a 90% confidence level cross-section upper limit of 30.9 pb for a mass of $0.76\mathrm{GeV}/{\mathrm{c}}^2$.

Interlayer rotation in van der Waals (vdW) materials offers a unique degree of freedom for manipulating lattice dynamics and leads to an exotic state with vanishing friction called structural superlubricity. Extensive theoretical calculations have also predicted the potential of twisted vdW materials for controlling heat flow in advanced electronics. However, precise experimental measurements have proven extremely challenging with only a handful of efforts to date reporting inconsistent results. Here, we have managed to achieve simultaneous mechanical characterizations and thermal measurements of the intrinsic twisted interfaces in microfabricated graphite mesas. Remarkably, the conductance of superlubric interfaces reaches about $600{\mathrm{MWm}}^{-2}{\mathrm{K}}^{-1}$ which surpasses the measured values for artificially stacked vdW structures by nearly an order of magnitude. Nonetheless, we successfully resolved over 30-fold variation of thermal conductance as the buried interfaces were rotated to a locked state. Further, atomic simulations revealed the predominant role of the transverse acoustic phonons. Together, our findings highlight a general physical picture that directly correlates interfacial thermal transport with sliding resistance, and lay the foundation for twist-enabled thermal management which are particularly beneficial to twistronics and slidetronics.

We show that energy dissipation in slowly driven, Markovian quantum systems at low temperature is linked to the geometry of the driving protocol through the quantum (or Fubini-Study) metric. Utilizing these findings, we establish lower bounds on dissipation rates in two-tone protocols, such as those employed for topological frequency conversion. Notably, in appropriate limits these bounds are only determined by the topology of the protocol and an effective quality factor of the system-bath coupling. Our results bridge topological and geometric phenomena with energy dissipation in open quantum systems, and further provide design principles for optimal driving protocols.

The Wigner-Smith time delay of flux conserving systems is a real quantity that measures how long an excitation resides in an interaction region. The complex generalization of time delay to non-Hermitian systems is still under development, in particular, its statistical properties in the short-wavelength limit of complex chaotic scattering systems has not been investigated. From the experimentally measured multiport scattering ($S$) matrices of one-dimensional graphs, a two-dimensional billiard, and a three-dimensional cavity, we calculate the complex Wigner-Smith (${\tau }_{\mathrm{WS}}$), as well as each individual reflection (${\tau }_{xx}$) and transmission (${\tau }_{xy}$) time delay. The complex reflection time-delay differences (${\tau }_{\delta R}$) between each port are calculated, and the transmission time-delay differences (${\tau }_{\delta T}$) are introduced for systems exhibiting nonreciprocal scattering. Large time delays are associated with scattering singularities such as coherent perfect absorption, reflectionless scattering, slow light, and unidirectional invisibility. We demonstrate that the large-delay tails of the distributions of the real and imaginary parts of each time-delay quantity are superuniversal, independent of experimental parameters: wave propagation dimension $\mathcal{D}$, number of scattering channels $M$, Dyson symmetry class $\beta$, and uniform attenuation $\eta$. The tails determine the abundance of the singularities in generic scattering systems, and the superuniversality is in direct contrast with the well-established time-delay statistics of unitary scattering systems, where the tail of the ${\tau }_{\mathrm{WS}}$ distribution depends explicitly on the values of $M$ and $\beta$. We relate the distribution statistics to the topological properties of the corresponding singularities. Although the results presented here are based on classical microwave experiments, they are applicable to any non-Hermitian wave-chaotic scattering system in the short-wavelength limit, such as optical or acoustic resonators.

Physical networks can develop tuned responses, or functions, by design, by evolution, or by learning via local rules. In all of these cases, tunable degrees of freedom characterizing internal interactions are modified to lower a cost penalizing deviations from desired outputs. An important class of such networks follows dynamics that minimize a global physical quantity, or Lyapunov function, with respect to physical degrees of freedom. In such networks, learning is a “double optimization” process in which two quantities, one defined by the task and the other prescribed by physics, are minimized with respect to different but coupled sets of variables. Here, we show how this learning process couples the high-dimensional “cost landscape” to the “physical landscape,” linking the physical and cost Hessian matrices. Physical responses of trained networks to random perturbations thus reveal the functions to which they were tuned. Our results, illustrated using electrical networks with adaptable resistors, are generic to networks that perform tasks in the linear response regime.

Accurate and efficient theoretical techniques for describing ionic fluids are highly desirable for many applications across the physical, biological, and materials sciences. With a rigorous statistical mechanical foundation, classical density functional theory (cDFT) is an appealing approach, but the competition between strong Coulombic interactions and steric repulsion limits the accuracy of current approximate functionals. Here, we extend a recently presented machine learning (ML) approach [Sammüller et al., Proc. Natl. Acad. Sci. U.S.A., 120, e2312484120 (2023)] designed for systems with short-ranged interactions to ionic fluids. By adopting ideas from local molecular field theory, the framework we present amounts to using neural networks to learn the local relationship between the one-body direct correlation functions and inhomogeneous density profiles for a “mimic” short-ranged system, with effects of long-ranged interactions accounted for in a mean-field, yet well-controlled, manner. By comparing to results from molecular simulations, we show that our approach accurately describes the structure and thermodynamics of prototypical models for electrolyte solutions and ionic liquids, including size-asymmetric and multivalent systems. The framework we present acts as an important step toward extending ML approaches for cDFT to systems with accurate interatomic potentials.

We study an elastoplastic model of an amorphous solid subject to athermal quasistatic cyclic shear strain. We focus on cycling amplitudes in the so-called reversible-plastic regime where, after a transient, the system locks into a hysteretic limit cycle and returns to the same microscopic configuration after one or more strain cycles. We show that the ground state energy of the terminal limit cycle decreases with increasing cycling amplitude. In analogy to an annealed alloy or an aged colloidal glass, one would expect the states with lower energy to be mechanically harder and to require larger stresses and strains to trigger microscopic rearrangements. However, we show the opposite result: the systems with lower energy cycled at higher strain amplitude are mechanically softer and begin to exhibit plastic rearrangements at smaller stresses and strains within the cycle. We explain this anomaly quantitatively in terms of Eshelby inclusion theory where an inclusion is subjected to a particular negative stress value after it undergoes a yielding event. These results point the way toward measurements to be conducted in experiments and particle-based computer simulations on cyclically sheared amorphous solids.

It is known that the current of emitted electrons flowing through a plasma can saturate upon formation of a potential well adjacent to the cathode (the “space charge effect”). Here, we demonstrate another saturation mechanism that will often set a more restrictive limit on the global current. When “backflow saturation” occurs, the cathode sheath weakens to allow emitted electrons that already entered the plasma to backflow to the cathode. This effect could not be captured by studies modelling the cathode sheath by itself because its origin is coupled to processes in the interior plasma and anode sheath. By modeling a full plasma diode, we show that depending on conditions the global current can be limited in four ways; by backflow alone, by space charge alone, by both mechanisms in a stable cooperative form, or by both in a competing oscillatory form.

We show that the surface of a centrosymmetric, collinear, compensated antiferromagnet, which hosts bulk ferroically ordered magnetic octupoles, exhibits a linear magnetoelectric effect, a net magnetization, and a net electric dipole moment. Thus, the surface satisfies all the conditions of a multiferroic, in striking contrast to the bulk, which is neither polar nor exhibits any net magnetization or linear magnetoelectric response. Of particular interest is the case of nonrelativistic $d$-wave spin split antiferromagnets, in which the bulk magnetic octupoles and consequently the surface multiferroicity exist even without spin-orbit interaction. We illustrate our findings using first-principles calculations, taking ${\mathrm{FeF}}_2$ as an example material. Our Letter underscores the bulk-boundary correspondence in these unconventional antiferromagnets.

The classical Jarzynski equality establishes an exact relation between the stochastic work performed on a system driven out of thermal equilibrium and the free energy difference in a corresponding quasistatic process. This fluctuation theorem bears experimental relevance, as it enables the determination of the free energy difference through the measurement of externally applied work in a nonequilibrium process. In the quantum case, the Jarzynski equality only holds if the measurement procedure of the stochastic work is drastically changed: it is replaced by a so-called two-point measurement scheme that requires the knowledge of the initial and final Hamiltonian and therefore lacks the predictive power for the free energy difference that the classical Jarzynski equation is known for. Here, we propose a quantum fluctuation theorem that is valid for externally measurable quantum work determined during the driving protocol. In contrast to the two-point measurement case, the theorem also applies to open quantum systems and the scenario can be realized without knowing the system Hamiltonian. Our fluctuation theorem comes in the form of an inequality and therefore only yields bounds to the true free energy difference. The inequality is saturated in the quasiclassical case of vanishing energy coherences at the beginning and at the end of the protocol. Thus, there is a clear quantum disadvantage.

The eigenstate thermalization hypothesis (ETH) has been established as the general framework to understand quantum statistical mechanics. Only recently has the attention been paid to so-called full ETH, which accounts for higher-order correlations among matrix elements, and that can be rationalized theoretically using the language of free probability. In this work, we perform the first numerical investigation of the full ETH in physical many-body systems with local interactions by testing the decomposition of higher-order correlators into thermal free cumulants for local operators. We perform exact diagonalization on two classes of local nonintegrable (chaotic) quantum many-body systems: spin chain Hamiltonians and Floquet brickwork unitary circuits. We show that the dynamics of four-time correlation functions are encoded in fourth-order free cumulants, as predicted by ETH. Their dependence on frequency encodes the physical properties of local many-body systems and distinguishes them from structureless, rotationally invariant ensembles of random matrices.

We elucidate that a distinctive resonant excitation between quasinormal modes (QNMs) of black holes emerges as a universal phenomenon at an avoided crossing near the exceptional point through high-precision numerical analysis and theory of QNMs based on the framework of non-Hermitian physics. This resonant phenomenon not only allows us to decipher a long-standing mystery concerning the peculiar behaviors of QNMs but also stands as a novel beacon for characterizing black hole spacetime geometry. Our findings pave the way for rigorous examinations of black holes and the exploration of new physics in gravity.

In the context of planar conformal gauge theory, we study five-point correlation functions between the interaction Lagrangian and four of the lightest single-trace, gauge-invariant scalar primaries. After performing two light-cone operator product expansions (OPEs), we express this correlator in terms of the three-point functions between two leading-twist spinning operators and the Lagrangian. For finite values of spin, we compute these structure constants in perturbation theory up to two loops in $\mathcal{N}=4$ super Yang-Mills theory. Large values of spin are captured by null polygon kinematics, where we use dualities with null polygon Wilson loops as well as factorization properties to bootstrap the universal behavior of the structure constants at all loops. We find explicit maps that relate the Lagrangian structure constants with the leading-twist anomalous dimension. From the large-spin map, we recover the cusp anomalous dimension at strong and weak coupling, including genus-one terms.

We present the first nuclear cross-section measurements of $(\mathrm{p},\gamma )$ and (p,n) reactions on ${}^{118}\mathrm{Te}$ at energies relevant for the $\gamma$-process nucleosynthesis. Absolute cross-section values for center-of-mass energies of 6, 7 and 10 MeV are provided, together with a theoretical extrapolation to the Gamow window. This experiment marks the first time that direct proton-induced reactions have been measured on a radioactive ion beam at the Experimental Storage Ring (ESR) at GSI, Darmstadt. This paves the way for a large variety of measurements, delivering new constraints for explosive nucleosynthesis and for physics beyond nuclear stability.