We investigate anomalous spin and orbital Hall phenomena in antiferromagnetic materials via orbital pumping experiments. Conducting spin and orbital pumping experiments on $\mathrm{YIG}/\mathrm{Pt}/{\mathrm{Ir}}_{20}{\mathrm{Mn}}_{80}$ heterostructures, we unexpectedly observe strong spin and orbital anomalous signals in an out-of-plane configuration. We report a sevenfold increase in the signal of the anomalous inverse orbital Hall effect compared to conventional effects. Our study suggests expanding the orbital Hall angle (${\theta }_{\mathrm{OH}}$) to a rank 3 tensor, akin to the spin Hall angle (${\theta }_{\mathrm{SH}}$), to explain the anomalous inverse orbital Hall effect. This work pioneers converting spin-orbital currents into charge currents, advancing the spin-orbitronics domain in antiferromagnetic materials.

We investigate spin relaxation dynamics of interlayer excitons in a ${\mathrm{MoSe}}_2/{\mathrm{MoS}}_2$ heterostructure induced by the Rashba effect. In such a system, Rashba interactions arise from an out-of-plane electric field due to photogenerated interlayer excitons inducing a phonon-assisted intravalley spin relaxation. We develop a theoretical description based on a microscopic approach to quantify the magnitude of Rashba interactions and test these predictions via time-resolved Kerr rotation measurements. In agreement with the calculations, we find that the Rashba-induced intravalley spin mixing becomes the dominating spin relaxation channel above $T=70\mathrm{K}$. Our work identifies a previously unexplored spin-depolarization channel in heterostructures which can be used for ultrafast spin manipulation.

Chiral phonons possessing valley pseudoangular momentum (PAM) underlie a diversity of quantum phenomena of fundamental and applied importance, but are challenging to probe directly. We show that deficiencies of typical momentum-resolved electron energy loss measurements that make it impossible to distinguish the PAM of chiral phonons can be overcome by introducing pinwheel free electron states with well-defined PAM. Transitions between such states generate 2D periodic arrays of in-plane field vortices with polarization textures tailored to selectively couple to desired chiral mode symmetries.

The rectification phenomenon caused by the simultaneous breaking of time-reversal and spatial inversion symmetries has been extended to a wide range of (quasi)particles and waves; however, nonreciprocal diffraction, which is the imbalance of upward and downward deflections, was previously observed only for photons and remained to be extended to other (quasi)particles. In this Letter, we present evidence of the nonreciprocal diffraction of a surface acoustic wave (SAW) utilizing a magnetoelastic grating on a SAW device. Asymmetric diffraction intensities were observed when the ferromagnetic resonance was acoustically excited. Based on a theoretical model, we attribute the microscopic origin of this phenomenon to the resonant scattering involving ferromagnetic resonance excitations. The novel property may pave an avenue to further development of SAW devices for various purposes, including microwave communications and quantum engineering applications.

The kinetic uncertainty relation (KUR) bounds the signal-to-noise ratio of stochastic currents in terms of the number of transitions per unit time, known as the dynamical activity. This bound was derived in a classical context and can be violated in the quantum regime due to coherent effects. However, the precise connection between KUR violations and quantum coherence has so far remained elusive, despite significant investigation. In this Letter, we solve this problem by deriving a modified bound that exactly pinpoints how, and when, coherence might lead to KUR violations. Our bound is sensitive to the specific kind of unraveling of the quantum master equation. It, therefore, allows one to compare quantum jumps and quantum diffusion, and understand, in each case, how quantum coherence affects fluctuations. We illustrate our result on a double quantum dot, where the electron current is monitored either by electron jump detection or with continuous diffusive charge measurement.

We present measurements of the atmospheric depth of the shower maximum $X_{\max }$, inferred for the first time on an event-by-event level using the surface detector of the Pierre Auger Observatory. Using deep learning, we were able to extend measurements of the $X_{\max }$ distributions up to energies of 100 EeV (${10}^{20}\mathrm{eV}$), not yet revealed by current measurements, providing new insights into the mass composition of cosmic rays at extreme energies. Gaining a 10-fold increase in statistics compared to the fluorescence detector data, we find evidence that the rate of change of the average $X_{\max }$ with the logarithm of energy features three breaks at $6.5\pm 0.6(\mathrm{stat})\pm 1(\mathrm{syst})\mathrm{EeV}$, $11\pm 2(\mathrm{stat})\pm 1(\mathrm{syst})\mathrm{EeV}$, and $31\pm 5(\mathrm{stat})\pm 3(\mathrm{syst})\mathrm{EeV}$, in the vicinity to the three prominent features (ankle, instep, suppression) of the cosmic-ray flux. The energy evolution of the mean and standard deviation of the measured $X_{\max }$ distributions indicates that the mass composition becomes increasingly heavier and purer, thus being incompatible with a large fraction of light nuclei between 50 and 100 EeV.

Topological gapped crystalline materials are a class of topological materials characterized by invariants protected by spatial symmetries, allowing for the emergence of robust boundary states. The band topology of gapped materials with crystal symmetries can be theoretically labeled by symmetry-indicator invariants, such as the Fu-Kane parity criterion for inversion-symmetric topological gapped materials. Here, we propose an approach to measuring these invariants and diagnosing topological gapped crystalline materials, which is experimentally validated in two-dimensional photonic crystals with finite size. Notably, this diagnosis approach relies exclusively on the measured field distribution within the bulk region, without necessitating the energy band diagram possessing complete band gaps, even in the absence of in-gap states in real materials. Our study provides an approach for measuring symmetry-indicator invariants and paves the way for experimentally diagnosing various gapped topological phases originating from crystalline symmetries.

Carnot efficiency sets a fundamental upper bound on the heat engine efficiency, attainable in the quasistatic limit, albeit at the cost of completely sacrificing power output. Here, we present a minimal heat engine model that can attain Carnot efficiency while achieving maximum power output. We unveil the potential of intrinsic divergent physical quantities within the working substance, such as degeneracy, as promising thermodynamic resources to break through the universal power-efficiency trade-off imposed by nonequilibrium thermodynamics for conventional heat engines. Our findings provide novel insights into the collective advantage in harnessing energy of many-body interacting systems.

As the simplest model of transport of interacting particles in a disordered medium, we consider the asymmetric simple exclusion process (ASEP) in which particles with hard-core interactions perform biased random walks, on the supercritical percolation cluster. In this process, the long time trajectory of a marked particle consists of steps on the backbone, punctuated by time spent in side branches. We study the probability distribution in the steady state of the waiting time $T_w$ of a randomly chosen particle, in a side branch since its last step along the backbone. Exact numerical evaluation of this on a single side branch of length $L=1$ to 9 shows that for large fields, the probability distribution of $\log T_w$ has multiple well separated peaks. We extend this result to a regular comb, and to the ASEP on the percolation cluster. We show that in the steady state, the fractional number of particles that have been in the same side branch for a time interval greater than $T_w$ varies as $\exp (-c\sqrt{\log T_w})$ for large $T_w$, where $c$ depends only on the bias field. However, these long timescales are not reflected in the eigenvalue spectrum of the Markov evolution matrix. The system shows dynamical heterogeneity, with particles segregating into pockets of high and low mobilities.

Explicit mathematical reconstructions of quantum combs play a significant role in developing quantum information science. However, tremendous parameter requirements and physical constraint implementations have become computationally nonignorable encumbrances. In this Letter, we propose an efficient method for quantum comb tomography by learning isometries on the Stiefel manifold via solving a series of unconstrained optimization problems with significantly fewer parameters. The stepwise isometry estimation shows the capability for providing information of the truncated quantum comb while processing the tomography. Remarkably, this method enables the dimension-reduced quantum comb tomography by reducing the ancillary dimensions of isometries with bounded error. As a result, our proposed method exhibits high accuracy and efficiency.

The quantum Cramér-Rao bound (QCRB) stands as a cornerstone of quantum metrology. Yet, akin to its classical counterpart, it provides only local information and overlooks higher-order details. We leverage the theory of higher-order asymptotics to circumvent these issues, providing corrections to the performance of estimators beyond the QCRB. While the QCRB often yields a whole family of optimal states and several optimal measurements, our approach allows us to identify optimal states and measurements within the family that are otherwise equivalent according to the QCRB alone; these are requisite for optimal metrology before reaching the asymptotic limit. These results are especially pertinent when dealing with unitary processes.

We investigate the role of hyperfine structure in resonant-dipole interactions between two atoms cotrapped in an optical tweezer. Two-body loss rates from light-assisted collisions (LACs) are measured across the ${}^{87}\mathrm{Rb}$ hyperfine spectrum and connected to properties of molecular photoassociation potentials via a semiclassical model. To obtain our results, we introduce an imaging technique that leverages repulsive LACs to detect two atoms in a trap, thereby circumventing parity constraints in tweezers. Our findings offer key insights for exploiting hyperfine structure in laser-induced collisions to control cold atoms and molecules in a broad range of quantum science applications.

We propose a novel topological defect called Janus bound states in the continuum (BICs), featuring asymmetric topological charges in upward and downward radiation channels. Our approach involves a photonic crystal slab (PCS) that initially exhibits both out-of-plane and in-plane mirror symmetry, and this PCS possesses one BIC at the $\mathrm{\Gamma }$ point and two BICs off the $\mathrm{\Gamma }$ point. By introducing certain perturbations that break the out-of-plane mirror symmetry, the two off-$\mathrm{\Gamma }$ BICs decompose into four circularly polarized states ($C$ points) with identical topological charges (each with half the topological charge of the original BIC) while the at-$\mathrm{\Gamma }$ BIC is preserved. Then, we selectively manipulate the four $C$ points associated with the downward radiation channel to converge at the at-$\mathrm{\Gamma }$ BIC, forming a Janus BIC with distinct topological charges for upward and downward radiation. By further introducing in-plane mirror symmetry perturbation, we can bring two of the $C$ points with the same handedness and identical topological charges for upward radiation to merge into the Janus BIC. This process results in a Janus chiral BIC which exhibits large intrinsic chirality and an infinite $Q$ factor. Janus BICs can induce distinct Pancharatnam-Berry phase singularities in momentum space for different incident channels, providing a new approach to control orbital angular momentum. Janus chiral BICs hold promise in enhancing direction-dependent and spin-dependent asymmetric light-matter interaction, opening new pathways for improving chirality-dependent operation for on-chip devices.

Anharmonic atomic motions can strongly influence the optoelectronic properties of materials but how these effects are connected to the underlying phonon band structure is not understood well. We investigate how the electronic band gap is influenced by overdamped phonons, which occur in an intriguing regime of phonon-phonon interactions where vibrational lifetimes fall below one oscillation period. We contrast the anharmonic halide perovskite ${\mathrm{CsPbBr}}_3$, known to exhibit overdamped phonons in its cubic phase, with the anharmonic oxide perovskite ${\mathrm{SrTiO}}_3$ where the phonons are underdamped at sufficiently high temperatures. Our results show that overdamped phonons strongly impact the band gap and cause slow dynamic fluctuations of electronic levels that have been implicated in the unique optoelectronic properties of halide perovskites. This finding is enabled by developing augmented stochastic Monte Carlo methods accounting for phonon renormalization and imaginary modes that are typically neglected. Our work provides guidelines for capturing anharmonic effects in theoretical calculations of materials.

The Hubbard model at temperatures above the Néel transition, despite being a paramagnet, can exhibit rich physics due to the interplay of Fermi surface, on-site interaction $U$ and thermal fluctuations. Nevertheless, the understanding of the crossover physics remains only at a qualitative level, because of the intrinsically smooth behavior. Employing an improved variant of the numerically exact auxiliary-field quantum Monte Carlo algorithm equipped with numerical analytic continuation, we obtain a broad variety of thermodynamic and dynamical properties of the three-dimensional Hubbard model at half filling, quantitatively determine the crossover boundaries, and observe that the metal-insulator crossover regime, in which antiferromagnetic spin correlations appear strongest, exists over an extended regime in between the Fermi liquid for small $U$ and the Mott insulator for large $U$. In particular, the location of the most rapid suppression of double occupancy as $U$ increases, is found to fully reside in the metallic Fermi liquid regime, in contrast to the conventional intuition that it is a representative feature for entering the Mott insulator. Beside providing a reliable methodology for numerical study of crossover physics, our work can also serve as a timely and important guideline for the most recent optical lattice experiments.

We show that Hubbard models with nearest-neighbor hopping and a nearest-neighbor hardcore constraint exhibit “maximal” Hilbert space fragmentation in many lattices of arbitrary dimension $d$. Focusing on the $d=1$ rhombus chain and the $d=2$ Lieb lattice, we demonstrate that the fragmentation is strong for all fillings in the thermodynamic limit, and explicitly construct all emergent integrals of motion, which include an extensive set of higher-form symmetries. Blockades consisting of frozen particles partition the system in real space, leading to anomalous dynamics. Our results are potentially relevant to optical lattices of dipolar and Rydberg-dressed atoms.