Physical review letters最新文献

We provide arguments indicating that the semiclassical Einstein equations follow from quantum relative entropy and its proportionality to an area variation. Using modular theory, we establish that the relative entropy between the vacuum state and coherent excitations of a scalar quantum field on a bifurcate Killing horizon is given by the energy flux across the horizon. Under the assumption of the Bekenstein-Hawking entropy-area formula, this energy flux is proportional to a variation in the surface area of the horizon cross section. The semiclassical Einstein equations follow automatically from this identification. Our approach provides a quantum field theoretic generalization of Jacobson's thermodynamic derivation of the Einstein equations, replacing classical thermodynamic entropy with the well-defined quantum relative (Araki-Uhlmann) entropy. This suggests that quantum information plays a central role in what is often seen as a zeroth order approximation of a theory of quantum gravity, namely quantum field theory in curved spacetimes.

We investigate the localization transition of interacting particles in a one-dimensional system with colored-noise disorder, where backward scattering processes are suppressed beyond a cutoff. Employing two complementary renormalization group procedures, we derive the phase diagram and reveal a significant shift in the localization transition point, governed by correlations. Our numerical analysis further demonstrates that the scaling of the localization length with disorder strength deviates markedly from the conventional behavior observed in typical localized phases, highlighting the unique impact of correlated disorder on interacting quantum systems. Application to optical disorder used in cold atom experiments is discussed.

Conductive carbon additives in lithium-ion battery cathodes significantly increase electron transport, facilitating rapid charging. However, quantifying this improvement remains challenging. Momentum distribution of annihilating electron-positron pairs offers a powerful approach to selectively probe the O 2p orbitals in LiCoO_{2} microparticles and the 2p_{z} carbon orbitals in the conductive carbon additives. By analyzing this momentum distribution, we obtain the amplification of subtle electron momentum distribution signals from carbon π bonds. Ab initio modeling of LiCoO_{2} and various topologies of carbon structures reproducing the experimental momentum distribution helps to quantify the fraction of positron annihilation occurring within the carbon structures. Our theoretical results combined with earlier experimental findings reveal potential charge transport pathways in the LiCoO_{2}/C composite by quantifying the spectral contributions of electron transfer orbitals, which constitutes the nanoscale circuitry enabling efficient electron transport in battery cathodes.

We theoretically predict a spin-current analog of the quantized circular photogalvanic effect in Weyl semimetals. This phenomenon is forbidden in antiferromagnets by symmetry but uniquely allowed in altermagnets, highlighting a novel and intrinsic characteristic of altermagnetism. To systematically explore second-order spin current responses, we classify all symmetry-allowed responses based on spin point groups. Furthermore, we provide a comprehensive classification of altermagnetic Weyl semimetals by identifying spin space groups that host symmetry-enforced Weyl points. Utilizing this classification, we construct a symmetry-guided tight-binding model and confirm our predictions. Finally, we identify Weyl crossings in a material candidate via first-principle calculations. Our Letter unveils a distinctive optical response of altermagnets, paving the way for a new frontier in altermagnetism.

The amplification of magnetic fields is crucial for understanding the observed magnetization of stars and galaxies. Turbulent dynamo is the primary mechanism responsible for that but the understanding of its action in a collapsing environment is still rudimentary and relies on limited numerical experiments. We develop an analytical framework and perform numerical simulations to investigate the behavior of small-scale and large-scale dynamos in a collapsing turbulent cloud. This approach is also applicable to expanding environments and facilitates the application of standard dynamo theory to evolving systems. Using a supercomoving formulation of the magnetohydrodynamic equations, we demonstrate that dynamo action in a collapsing background leads to a superexponential growth of magnetic fields in time, significantly faster than the exponential growth seen in stationary turbulence. The enhancement is mainly due to the increasing eddy turnover rate during the collapse, which boosts the instantaneous growth rate of the dynamo. We also show that the scaling of final saturated magnetic field strength with density robustly exceeds the expectation from considerations of pure flux-freezing. Apart from establishing a formal framework for studying magnetic field evolution in collapsing (or expanding) turbulent plasmas, these findings suggest that during star and galaxy formation magnetic fields can become dynamically relevant much earlier than previously thought.

The current phase relation (CPR) determines the electromagnetic response of Josephson junctions in superconducting circuits. It is sensitive to the weak link materials and interface quality. In this work, we report the intrinsic Josephson effect originating from domains in the single-crystal kagome superconductor CsV_{3}Sb_{5}, where no artificial weak links were introduced. By tuning the magnetic flux, we observe the Josephson diode effect and clear half-integer Shapiro steps. The quantitative analysis reveals a significantly enhanced second harmonic content in the CPR, exceeding the ballistic limit of a single Andreev Josephson junction. Such a pronounced second harmonic component is attributed to the nonuniformity of the current distribution and the nonsinusoidal CPR in highly transparent intrinsic Josephson junctions. The intrinsic Josephson junction formed at the domain wall shows the potential application for superconducting quantum technologies.

Given a triangulation of a closed orientable surface, we place single-mode resonators or single-orbital artificial atoms at its vertices, edges, and facets, and we devise near-neighbor hopping terms derived from the boundary and Poincaré duality maps of the simplicial complex of the triangulation. Regardless of the surface or its triangulation, these terms always lead to tight-binding Hamiltonians with large and clean topological spectral gaps, carrying non-trivial Chern numbers in the limit of infinite refinement of the triangulation. We confirm this via numerical simulations, and demonstrate how these models enable topological edge modes at the surfaces of real-world objects. Furthermore, we describe a metamaterial whose dynamics reproduces that of the proposed model, thus bringing the topological metamaterials closer to real-world applications.

The anti-P-pseudo-Hermitian system has recently been recognized as a new avenue in non-Hermitian physics, exhibiting symmetry-related phenomena without the need for time-reversal symmetry. However, its physical realization remains challenging due to the difficulty of integrating tunable media while simultaneously enabling nonreciprocal coupling. In this Letter, we introduce a novel framework for constructing an anti-P-pseudo-Hermitian mechanical system by incorporating piezoelectric actuators and sensors with nonreciprocal coupling into mechanical beams. We theoretically demonstrate that this system can exhibit programmable exceptional points (EPs) and validate our approach numerically and experimentally. Precise tuning of EPs is crucial for optimizing the system's sensitivity under operational conditions. As a key demonstration, we show that this system excels in detecting minute mass variations, making it highly effective for ultrasensitive sensing applications. This Letter not only advances the understanding of non-Hermitian physics, but also lays the groundwork for the next generation of mechanical sensors based on EP physics.

We present and test a protocol to learn the matrix-product operator (MPO) representation of an experimentally prepared quantum state. The protocol takes as input classical shadows corresponding to local randomized measurements, and outputs the tensors of an MPO maximizing a suitably defined fidelity with the experimental state. The tensor optimization is carried out sequentially, similarly to the well-known density matrix renormalization group algorithm. Our approach is provably efficient under certain technical conditions expected to be met in short-range correlated states and in typical noisy experimental settings. Under the same conditions, we also provide an efficient scheme to estimate fidelities between the learned and the experimental states. We experimentally demonstrate our protocol by learning entangled quantum states of up to N=96 qubits in a superconducting quantum processor. Our method upgrades classical shadows to large-scale quantum computation and simulation experiments.

Landau levels (LLs) are the massively degenerate discrete energy spectra of charged particles in a transverse magnetic field, and they lie at the heart of many intriguing phenomena, such as the integer and fractional quantum Hall effects as well as quantized vortices. In this Letter, we consider coupling of LLs of a transversely driven, single charge-neutral particle in a synthetic gauge potential to a quantized field of an optical cavity-a setting reminiscent of superradiant self-ordering setups in quantum gases. We uncover that this complex system can be, surprisingly, described in terms of two highly nonlinearly coupled quantum harmonic oscillators, thus enabling a full quantum mechanical treatment. Light-matter coupling mixes the LLs and the superradiant photonic mode, leading to the formation of hybrid states referred to as "Landau polaritons." They partially inherit the degeneracy of the LLs and possess intriguing features such as nonzero light-matter entanglement and quadrature squeezing. Depending on the system parameters and the choice of initial state, the system exhibits diverse nonequilibrium quantum dynamics and multiple steady states with distinct physical properties. This Letter lays the foundation for further investigating the novel, driven-dissipative Landau-polariton physics in quantum-gas-cavity-QED settings.