We present a heralded state preparation scheme for driven nonlinear open quantum systems. The protocol is based on a continuous photon counting measurement of the system's decay channel. When no photons are detected for a period of time, the system has relaxed to a measurement-induced pseudosteady state. We illustrate the protocol by the creation of states with a negative Wigner function in a Kerr oscillator, a system whose unconditional steady state is strictly positive.

We use quantum electrodynamics and the confinement-induced nonlocal dielectric response model based on the Keldysh-Rytova electron interaction potential to study the epsilon-near-zero modes of metallic films in the transdimensional regime. Peculiar effects are revealed such as the plasmon mode degeneracy lifting and the dipole emitter coupling to the split epsilon-near-zero modes, leading to thickness-controlled spontaneous decay with rates increased by up to three orders of magnitude.

Interaction-driven symmetry breaking in a metallic (doped) Dirac system can manifest in the spontaneous gap generation at the nodal point buried below the Fermi level. Across this transition linear conductivity remains finite, making its direct observation difficult in linear transport. We propose the nonlinear Hall effect as a direct probe of this transition when inversion symmetry is broken. Specifically, for a two-dimensional Dirac material with a tilted low-energy dispersion, we predict a transformation of the characteristic interband resonance peak into a non-Lorentzian form in the collisionless regime. Furthermore, we show that inversion-symmetry-breaking quantum phase transition is controlled by an exotic tilt-dependent line of critical points. As this line is approached from the ordered side, the nonlinear Hall conductivity is suppressed owing to the scattering between the strongly coupled incoherent fermionic and bosonic excitations. Our results should motivate further studies of nonlinear responses in strongly interacting Dirac materials.

We demonstrate gravity compensation for an ultracold gas of ${}^{87}\mathrm{Rb}$ atoms with a time-averaged optical potential. The position of a far-off-resonance beam is temporally modulated with an acousto-optic deflector to efficiently produce a potential with a linear gradient independent of the atomic magnetic sublevels. We realize compensation of the gravity sag and preparation of a degenerate gas in a trap with weak vertical confinement. Optical gravity compensation will provide the opportunity to perform experiments under microgravity in a laboratory and broaden the scope of cold atom research.

We investigate the collective colloidal current that emerges when strongly confined magnetic microspheres are subjected to a biased, but spatially uniform, precessing magnetic field. We observe a net bidirectional current composed of colloidal particles which periodically meet assembling into rotating dimers, and exchange their positions in a characteristic, “ceilidh”-like dance. We develop a theoretical model which explains the physics of the observed phenomena as dimer rupture and onset of current, showing agreement with Brownian dynamic simulations. By varying the tilt angle and the frequency of the applied field, we discover two separate transport mechanisms based on different ways the dimers break up during particle transport. Our results demonstrate an effective technique to drive microscale matter by using a combination of confinement and homogeneous field modulations, not based on any gradient of the applied field.

We report a strain-induced direct-to-indirect band gap transition in mechanically deformed $\mathrm{W}{\mathrm{S}}_2$ monolayers (MLs). The necessary amount of strain is attained by proton irradiation of bulk $\mathrm{W}{\mathrm{S}}_2$ and the ensuing formation of 1-ML-thick, ${\mathrm{H}}_2$-filled domes. The electronic properties of the curved MLs are mapped by spatially and time-resolved microphotoluminescence, revealing the mechanical stress conditions that trigger the variation of the band gap character. This general phenomenon, also observed in $\mathrm{Mo}{\mathrm{S}}_2$ and $\mathrm{WS}{\mathrm{e}}_2$, further increases our understanding of the electronic structure of transition metal dichalcogenide MLs and holds a great relevance for their optoelectronic applications.

We study bond percolation on several four-dimensional (4D) lattices, including the simple (hyper) cubic (SC), the SC with combinations of nearest neighbors and second nearest neighbors (SC-NN+2NN), the body-centered-cubic (bcc), and the face-centered-cubic (fcc) lattices, using an efficient single-cluster growth algorithm. For the SC lattice, we find $p_c=0.1601312\left(2\right)$, which confirms previous results (based on other methods), and find a new value $p_c=0.035827\left(1\right)$ for the SC-NN+2NN lattice, which was not studied previously for bond percolation. For the 4D bcc and fcc lattices, we obtain $p_c=0.074212\left(1\right)$ and $0.049517\left(1\right)$, which are substantially more precise than previous values. We also find critical exponents $\tau =2.3135\left(5\right)$ and $\mathrm{\Omega }=0.40\left(3\right)$, consistent with previous numerical results and the recent four-loop series result of Gracey [Phys. Rev. D 92, 025012 (2015)].

“Magnetic monopole” is an exotic quantum excitation in three-dimensional U(1) spin liquid, and its emergence is purely of quantum origin and has no classical analog. We predict topological thermal Hall effect (TTHE) of “magnetic monopoles” and present this prediction through non-Kramers doublets on a pyrochlore lattice. We observe that when the external magnetic field polarizes the Ising component of the local moment, internally this corresponds to the induction of emergent dual U(1) gauge flux for the “magnetic monopoles.” The motion of “magnetic monopoles” is then twisted by the induced dual U(1) gauge flux. This emergent Lorentz force on “magnetic monopoles” is the fundamental origin of TTHE. Therefore, TTHE would be a direct evidence of the “monopole” gauge coupling and the emergent U(1) gauge structure in pyrochlore U(1) spin liquid. Our result does not depend strongly on our choice of non-Kramers doublets for our presentation and can be well extended to Kramers doublets. Our prediction can be readily tested among the pyrochlore spin liquid candidate materials. We give a detailed discussion about the expectation for different pyrochlore magnets.

We present a unified description of the response of the hyperhoneycomb Kitaev magnet $\beta -{\text{Li}}_2{\text{IrO}}_3$ to applied magnetic fields along the orthorhombic directions $\mathbf{a}$, $\mathbf{b}$, and $\mathbf{c}$. This description is based on the minimal nearest-neighbor $J-K-\mathrm{\Gamma }$ model and builds on the idea that the incommensurate counter-rotating order observed experimentally at zero field can be treated as a long-distance twisting of a nearby commensurate order with six spin sublattices. The results reveal that the behavior of the system for $\mathbf{H}\parallel \mathbf{a}$, $\mathbf{H}\parallel \mathbf{b}$, and $\mathbf{H}\parallel \mathbf{c}$ share a number of qualitative features, including (i) a strong intertwining of the modulated, counter-rotating order with a set of uniform orders; (ii) the disappearance of the modulated order at a critical field $H^{*}$, whose value is strongly anisotropic with $H_{\mathbf{b}}^{*}<H_{\mathbf{c}}^{*}\ll H_{\mathbf{a}}^{*}$; (iii) the presence of a robust zigzag phase above $H^{*}$; and (iv) the fulfillment of the Bragg peak intensity sum rule. It is noteworthy that the disappearance of the modulated order for $\mathbf{H}\parallel \mathbf{c}$ proceeds via a “metamagnetic” first-order transition which does not restore all broken symmetries. This implies the existence of a second finite-$T$ phase transition at higher magnetic fields. We also demonstrate that quantum fluctuations give rise to a significant reduction of the local moments for all directions of the field. The results for the total magnetization for $\mathbf{H}\parallel \mathbf{b}$ are consistent with available data and confirm a previous assertion that the system is very close to the highly frustrated $K-\mathrm{\Gamma }$ line in parameter space. Our predictions for the magnetic response for fields along $\mathbf{a}$ and $\mathbf{c}$ await experimental verification.

Weyl semimetals (WSMs) are characterized by topologically stable pairs of nodal points in the band structure that typically originate from splitting a degenerate Dirac point by breaking symmetries such as time-reversal or inversion symmetry. Within the independent-electron approximation, the transition between an insulating state and a WSM requires the local creation or annihilation of one or several pairs of Weyl nodes in reciprocal space. Here, we show that strong electron-electron interactions may qualitatively change this scenario. In particular, we reveal that the transition to a Weyl semimetallic phase can become discontinuous, and, quite remarkably, pairs of Weyl nodes with a finite distance in momentum space suddenly appear or disappear in the spectral function. We associate this behavior with the buildup of strong many-body correlations in the topologically nontrivial regions, manifesting in dynamical fluctuations in the orbital channel. We also highlight the impact of electronic correlations on the Fermi arcs.

Symmetry indicators have proven to be extremely helpful in identifying topological crystalline insulators using symmetry-group representations of their Bloch states. An extension of this approach to superconducting systems requires defining an appropriate atomic limit for Bogoliubov-de-Gennes Hamiltonians. Here, we introduce such a notion of atomic limit and derive a ${\mathbb{Z}}_{2^d}$-valued symmetry indicator for inversion-symmetric superconductors in $d$ dimensions. This indicator allows for a refined topological classification including higher-order phases for systems in the superconducting symmetry classes D and DIII. We further elucidate their bulk-boundary correspondence using Dirac surface theories. Requiring only the normal-state band structure and the superconducting order-parameter symmetry as input, this indicator is well suited for a search of topological superconductors using first-principles calculations.

The multiferroic ferrimagnet ${\mathrm{Cu}}_2{\mathrm{OSeO}}_3$ with a chiral crystal structure has attracted a lot of recent attention due to the emergence of a magnetic skyrmion order in this material. Here, the topological properties of its magnon excitations are systematically investigated by linear spin-wave theory and inelastic neutron scattering. When considering Heisenberg exchange interactions only, two degenerate Weyl magnon nodes with topological charges $\pm 2$ are observed at high-symmetry points. Each Weyl point splits into two as the symmetry of the system is further reduced by including into consideration the nearest-neighbor Dzyaloshinskii-Moriya interaction, crucial for obtaining an accurate fit to the experimental spin-wave spectrum. Also, one additional pair of Weyl points appears near the $\mathbf{R}$ point. The predicted topological properties are verified by surface state and Chern number analysis. Additionally, we predict that a measurable thermal Hall conductivity can be associated with the emergence of the Weyl points, the position and number of which can be tuned by modifying the Dzyaloshinskii-Moriya interaction in the system.

We report on the experimental observation of the direct decay of a core vacancy in van der Waals clusters by emission of a fast electron from a neighboring atom. The process can be regarded as an interatomic Coulombic decay of core holes (core-level ICD). We identify it unambiguously by electron-electron and electron-electron-photon coincidence spectroscopy of the decay of $2p$ vacancies in Ar clusters. While several earlier works reported the absence of this channel, we find core-level ICD to be of considerable significance and quantify the branching ratio of this nonlocal electron emission to conventional local Auger decay as ($0.8\pm 0.2$)%. Our results are supported by calculations on smaller clusters and show a reasonable agreement. This report on a successfully performed electron-electron-photon coincidence experiment provides a perspective for explorations of matter exposed to ionizing radiation. The observed core-level ICD is proposed to be of general importance for studies on charge redistribution after core-level photoionization where van der Waals clusters are often used as prototype systems.

We discuss magnetically ordered states, arising in Heisenberg-Kitaev and related spin models, on three-dimensional (3D) harmonic honeycomb lattices. For large classes of ordered states, we show that they can be mapped onto two-dimensional (2D) counterparts on the honeycomb lattice, with the classical energetics being identical in the 2D and 3D cases. As an example, we determine the phase diagram of the classical nearest-neighbor Heisenberg-Kitaev model on the hyperhoneycomb lattice in a magnetic field: this displays rich and complex behavior akin to its 2D counterpart, with most phases and phase boundaries coinciding exactly. To make contact with the physics of the hyperhoneycomb iridate $\beta -{\mathrm{Li}}_2{\mathrm{IrO}}_3$, we also include a symmetric off-diagonal $\mathrm{\Gamma }$ interaction, discuss its 3D-2D mapping, and determine the relevant phase diagrams. In particular, we demonstrate explicitly the adiabatic equivalence of the spiral magnetic orders in $\alpha$- and $\beta -{\mathrm{Li}}_2{\mathrm{IrO}}_3$. Our results pave the way to a systematic common understanding of 2D and 3D Kitaev materials.

We present a full description of the nonergodic properties of wave functions on random graphs without boundary in the localized and critical regimes of the Anderson transition. We find that they are characterized by two critical localization lengths: the largest one describes localization along rare branches and diverges with a critical exponent ${\nu }_{\parallel }=1$ at the transition. The second length, which describes localization along typical branches, reaches at the transition a finite universal value (which depends only on the connectivity of the graph), with a singularity controlled by a new critical exponent ${\nu }_{\perp }=1/2$. We show numerically that these two localization lengths control the finite-size scaling properties of key observables: wave-function moments, correlation functions, and spectral statistics. Our results are identical to the theoretical predictions for the typical localization length in the many-body localization transition, with the same critical exponent. This strongly suggests that the two transitions are in the same universality class and that our techniques could be directly applied in this context.

First passage processes often seem to defy common sense. For example, consider a particle diffusing toward a target in a spherically symmetric confined system. One might naively expect that the hitting angle distribution as the confining boundary recedes to infinity would be the same as for an unbounded system. Here we show that this may or may not be true depending on the spatial dimension. In two dimensions, the limiting hitting distribution corresponds to that of the unbounded system, while in three (or more) dimensions the two differ by a nonintuitive additive constant, even when one accounts for the well-known finite probability that the particle never reaches the target. Confinement has other subtle effects on the features of the angular hitting distribution. For example, depending on the dimension and the starting distance from the target, the boundary may differentially favor arrival opposite to the entry point and lead to a maximum in the three-dimensional variance of the hitting angle statistics.

We uncover an unexpected family of in-gap chiral edge states in noninverted spin-1 Dirac quantum dots. The system represents a topologically trivial confinement configuration where such edge states are not expected according to the conventional wisdom. In particular, for a massive type of confining potential, two distinct situations can arise: with or without mass sign change, corresponding to a quantum dot with or without band inversion, respectively. The former case is conventional, where topologically protected chiral edge modes can arise in the gap. For the latter, contrary to the belief that there should be no one-way current-carrying edge channels, we find the surprising emergence of such edge states and the spin-1 analog of Majorana modes. These states are strikingly robust and immune to backscattering. In the presence of a magnetic field, the edge states result in peculiar Fock-Darwin states originated from Landau-level confinement. The unexpected phenomenon is also validated in systems with bulk-topology regularization through (1) a properly regularized continuum model and (2) an experimentally accessible tight-binding dice lattice system.

Spin Hamiltonian engineering in solid-state systems plays a key role in a variety of applications ranging from quantum information processing and quantum simulations to novel studies of many-body physics. By analyzing the irreducible form of a general two-body spin-1/2 Hamiltonian, we identify all interchangeable interaction terms using rotation pulses. Based on this identification, we derive pulse sequences, defined by an icosahedral symmetry group, providing the most general achievable manipulation of interaction terms. We demonstrate that, compared to conventional Clifford rotations, these sequences offer advantages for creating Zeeman terms essential for magnetic sensing and could be utilized to generate interaction forms unreachable by standard rotations. The exact series of pulses required to generate desired interaction terms can be determined from a linear programming algorithm. For realizing the sequences, we propose two experimental approaches involving pulse product decomposition and off-resonant driving. The resulting engineered Hamiltonians could contribute to the understanding of many-body physics, and result in the creation of quantum simulators and the generation of highly entangled states, thereby opening avenues in quantum sensing and information processing.

Thermodynamic uncertainty relations quantifying a trade-off between current fluctuation and entropy production have been found in various stochastic systems. Herein, we study the thermodynamic uncertainty relations for Langevin systems driven by an external control protocol. Using information-theoretic techniques, we derive the uncertainty relations for arbitrary observables satisfying a scaling condition in both overdamped and underdamped regimes. We prove that the observable fluctuation is constrained by both entropy production and a kinetic term. The derived bounds are applicable to both current and noncurrent observables, and hold for arbitrary time-dependent protocols, thus providing a wide range of applicability. We illustrate our universal bounds with the help of three systems: a dragged Brownian particle, a Brownian gyrator, and a stochastic underdamped heat engine.

Insulating quantum magnets lie at the forefront both of fundamental research into quantum matter and of technological exploitation in the increasingly applied field of spintronics. In this context, the magnetic thermal transport is a particularly sensitive probe of the elementary spin and exotic topological excitations in unconventional magnetic materials. However, magnetic contributions to heat conduction are invariably intertwined with lattice (phonon) contributions, and thus the issue of spin-phonon coupling in determining the spin and thermal transport properties of magnetic insulators becomes more important with every emergent topological magnetic system. Here we report the observation of an anomalously strong enhancement of the thermal conductivity, occurring at all relevant temperatures, in the layered honeycomb material ${\mathrm{CrCl}}_3$ in the presence of an applied magnetic field. Away from the magnetically ordered phase at low temperatures and small fields, there is no coherent spin contribution to the thermal conductivity, and hence the effect must be caused by strong suppression of the phonon thermal conductivity due to magnetic fluctuations, which are in turn suppressed by the field. We build an empirical model for the thermal conductivity of ${\mathrm{CrCl}}_3$ within a formalism assuming an independently determined number of spin-flip processes and an efficiency of the phonon scattering events they mediate. By extracting the intrinsic phonon thermal conductivity, we obtain a quantitative description of our measured data at all fields and temperatures, and we demonstrate that the scattering efficiency is entirely independent of the applied field. In this way, we use ${\mathrm{CrCl}}_3$ as a model system to understand the interactions between spin and phonon excitations in the context of thermal transport. We anticipate that the completely general framework we introduce will have broad implications for the interpretation of transport phenomena in magnetic quantum materials.