The numerical renormalization group (NRG) is tailored to describe interacting impurity models in equilibrium, but it faces limitations for steady-state nonequilibrium, arising, e.g., due to an applied bias voltage. We show that these limitations can be overcome by describing the thermal leads using a thermofield approach, integrating out high energy modes using NRG, and then treating the nonequilibrium dynamics at low energies using a quench protocol, implemented using the time-dependent density matrix renormalization group. This yields quantitatively reliable results for the current (with errors $\lesssim 3\%$) down to the exponentially small energy scales characteristic of impurity models. We present results of benchmark quality for the temperature and magnetic field dependence of the zero-bias conductance peak for the single-impurity Anderson model.

Using a recent time-of-flight measurement technique with 1 ps time resolution and electron-energy spectroscopy, we develop a method to measure the longitudinal-optical-phonon emission rate of hot electrons traveling along a depleted edge of a quantum Hall bar. Comparison to a single-particle model implies the scattering mechanism involves a two-step process via an intra-Landau-level transition. We show that this can be suppressed by control of the edge potential profile, and a scattering length $>1\mathrm{mm}$ can be achieved, allowing the use of this system for scalable single-electron device applications.

We experimentally and numerically investigate the sudden expansion of fermions in a homogeneous one-dimensional optical lattice. For initial states with an appreciable amount of doublons, we observe a dynamical phase separation between rapidly expanding singlons and slow doublons remaining in the trap center, realizing the key aspect of fermionic quantum distillation in the strongly interacting limit. For initial states without doublons, we find a reduced interaction dependence of the asymptotic expansion speed compared to bosons, which is explained by the interaction energy produced in the quench.

We report on spin dynamics of individual, localized neutral impurities immersed in a Bose-Einstein condensate. Single cesium atoms are transported into a cloud of rubidium atoms and thermalize with the bath, and the ensuing spin exchange between localized impurities with quasispin $F_i=3$ and bath atoms with $F_b=1$ is resolved. Comparing our data to numerical simulations of spin dynamics, we find that, for gas densities in the Bose-Einstein condensate regime, the dynamics is dominated by the condensed fraction of the cloud. We spatially resolve the density overlap of impurities and gas by the spin population of impurities. Finally, we trace the coherence of impurities prepared in a coherent superposition of internal states when coupled to a gas of different densities. For our choice of states, we show that, despite high bath densities and, thus, fast thermalization rates, the impurity coherence is not affected by the bath, realizing a regime of sympathetic cooling while maintaining internal state coherence. Our work paves the way toward the nondestructive probing of quantum many-body systems via localized impurities.

A central task towards building a practical quantum computer is to protect individual qubits from decoherence while retaining the ability to perform high-fidelity entangling gates involving arbitrary two qubits. Here we propose and demonstrate a dephasing-insensitive procedure for storing and processing quantum information in an all-to-all connected superconducting circuit involving multiple frequency-tunable qubits, each of which can be controllably coupled to any other through a central bus resonator. Although it is generally believed that the extra frequency tunability enhances the control freedom but induces more dephasing impact for superconducting qubits, our results show that any individual qubit can be dynamically decoupled from dephasing noise by applying a weak continuous and resonant driving field whose phase is reversed in the middle of the pulse. More importantly, we demonstrate a new method for realizing a two-qubit phase gate with inherent dynamical decoupling via the combination of continuous driving and qubit-qubit swapping coupling. We find that the weak continuous driving fields not only enable the conditional dynamics essential for quantum information processing, but also protect both qubits from dephasing during the gate operation.

The Loschmidt echo is a purely quantum-mechanical quantity whose determination for large quantum many-body systems requires an exceptionally precise knowledge of all eigenstates and eigenenergies. One might therefore be tempted to dismiss the applicability of any approximations to the underlying time evolution as hopeless. However, using the fully connected transverse-field Ising model as an example, we show that this indeed is not the case and that a simple semiclassical approximation to systems well described by mean-field theory is, in fact, in good quantitative agreement with the exact quantum-mechanical calculation. Beyond the potential to capture the entire dynamical phase diagram of these models, the method presented here also allows for an intuitive geometric interpretation of the fidelity return rate at any temperature, thereby connecting the order parameter dynamics and the Loschmidt echo in a common framework. Videos of the postquench dynamics provided in Supplemental Material visualize this new point of view.

We propose a $D$-dimensional generalization of 4D biscalar conformal quantum field theory recently introduced by Gürdogan and one of the authors as a particular strong-twist limit of $\gamma$-deformed $N=4$ supersymmetric Yang-Mills theory. Similar to the 4D case, the planar correlators of this $D$-dimensional theory are conformal and dominated by “fishnet” Feynman graphs. The dynamics of these graphs is described by the integrable conformal $SO(1,D+1)$ spin chain. In 2D, it is the analogue of Lipatov’s $SL(2,C)$ spin chain for the Regge limit of QCD but with the spins $s=1/4$ instead of $s=0$. Generalizing recent 4D results of Grabner, Gromov, Korchemsky, and one of the authors to any $D$, we compute exactly at any coupling a four-point correlation function dominated by the simplest fishnet graphs of cylindric topology and extract from it exact dimensions of operators with chiral charge 2 and any spin together with some of their operator product expansion structure constants.

We study the nature of the electroweak phase transition (EWPT) in models where the Higgs boson emerges as a pseudo-Nambu-Goldstone boson of an approximate global symmetry of a new strongly interacting sector confining around the TeV scale. Our analysis focuses for the first time on the case where the EWPT is accompanied by the confinement phase transition of the strong sector. We describe the confinement in terms of the dilaton, the pseudo-Nambu-Goldstone boson of spontaneously broken conformal invariance of the strong sector. The dilaton can either be a mesonlike or a glueball-like state and we demonstrate a significant qualitative difference in their dynamics. We show that the EWPT can naturally be strongly first order, due to the nearly conformal nature of the dilaton potential. Furthermore, we examine the sizable scale variation of the Higgs potential parameters during the EWPT. In particular, we consider in detail the case of a varying top quark Yukawa coupling, and show that the resulting $CP$ violation is sufficient for successful electroweak baryogenesis. We demonstrate that this source of $CP$ violation is compatible with existing flavor and $CP$ constraints. Our scenario can be tested in complementary ways: by measuring the $CP$-odd top Yukawa coupling in electron electric dipole moment experiments, by searching for dilaton production and deviations in Higgs couplings at colliders, and through gravitational waves at LISA.

We report first measurements of $e^{+}{e}^{-}$ pair production in the mass region $0.4<M_{ee}<2.6\mathrm{GeV}/c^2$ at low transverse momentum ($p_T<0.15\mathrm{GeV}/c$) in noncentral $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$ and $\mathrm{U}+\mathrm{U}$ collisions at $\sqrt{s_{NN}}=193\mathrm{GeV}$. Significant enhancement factors, expressed as ratios of data over known hadronic contributions, are observed in the 40%–80% centrality of these collisions. The excess yields peak distinctly at low $p_T$ with a width ($\sqrt{⟨p_T^2⟩}$) between 40 and $60\mathrm{MeV}/c$. The absolute cross section of the excess depends weakly on centrality, while those from a theoretical model calculation incorporating an in-medium broadened $\rho$ spectral function and radiation from a quark gluon plasma or hadronic cocktail contributions increase dramatically with an increasing number of participant nucleons. Model calculations of photon-photon interactions generated by the initial projectile and target nuclei describe the observed excess yields but fail to reproduce the $p_T^2$ distributions.

We demonstrate a new principle of the laser-induced hammer-hit vibration of a micron-sized black sphere in liquid glycerol with a single divergent Gaussian beam. The light-induced $\mathrm{\Delta }\alpha$-photophoretic force, which is significantly improved by the vibrating speed of the microparticle, is responsible for both the pushing and pulling force of the hammer-hit vibration. Our approach expands the optical manipulation of microparticle hammer-hit vibration to a liquid medium and provides full control over the trapped particles, including the adjustment of the vibration frequency, amplitude, and position.

The two-dimensional oscillatory crack instability, experimentally observed in a class of brittle materials under strongly dynamic conditions, has been recently reproduced by a nonlinear phase-field fracture theory. Here, we highlight the universal character of this instability by showing that it is present in materials exhibiting widely different near crack tip elastic nonlinearity, and by demonstrating that the oscillations wavelength follows a universal master curve in terms of dissipation-related and nonlinear elastic intrinsic length scales. Moreover, we show that upon increasing the driving force for fracture, a high-velocity tip-splitting instability emerges, as experimentally demonstrated. The analysis culminates in a comprehensive stability phase diagram of two-dimensional brittle fracture, whose salient properties and topology are independent of the form of near tip nonlinearity.

Short pulse, high contrast, intense laser pulses incident onto a solid target are not known to generate fast neutral atoms. Experiments carried out to study the recombination of accelerated protons show a 200 times higher neutralization than expected. Fast neutral atoms can contribute to 80% of the fast particles at 10 keV, falling rapidly for higher energy. Conventional charge transfer and electron-ion recombination in a high density plasma plume near the target is unable to explain the neutralization. We present a model based on the copropagation of electrons and ions wherein recombination far away from the target surface accounts for the experimental measurements. A novel experimental verification of the model is also presented. This study provides insights into the closely linked dynamics of ions and electrons by which neutral atom formation is enhanced.

Using soft x-ray angle-resolved photoemission spectroscopy we probed the bulk electronic structure of $T_d\text{−}{\mathrm{MoTe}}_2$. We found that on-site Coulomb interaction leads to a Lifshitz transition, which is essential for a precise description of the electronic structure. A hybrid Weyl semimetal state with a pair of energy bands touching at both type-I and type-II Weyl nodes is indicated by comparing the experimental data with theoretical calculations. Unveiling the importance of Coulomb interaction opens up a new route to comprehend the unique properties of ${\mathrm{MoTe}}_2$, and is significant for understanding the interplay between correlation effects, strong spin-orbit coupling and superconductivity in this van der Waals material.

The law of reflection states that smooth surfaces reflect waves specularly, thereby acting as a mirror. This law is insensitive to disorder as long as its length scale is smaller than the wavelength. Monolayer graphene exhibits a linear dispersion at low energies and consequently a diverging Fermi wavelength. We present proof that for a disordered graphene boundary, resonant scattering off disordered edge modes results in diffusive electron reflection even when the electron wavelength is much longer than the disorder correlation length. Using numerical quantum transport simulations, we demonstrate that this phenomenon can be observed as a nonlocal conductance dip in a magnetic focusing experiment.

Breakdown of the quantum Hall effect (QHE) is commonly associated with an electric field approaching the inter-Landau-level (LL) Zener field, the ratio of the Landau gap and the cyclotron radius. Eluded in semiconducting heterostructures, in spite of extensive investigation, the intrinsic Zener limit is reported here using high-mobility bilayer graphene and high-frequency current noise. We show that collective excitations arising from electron-electron interactions are essential. Beyond a noiseless ballistic QHE regime a large super-Poissonian shot noise signals the breakdown via inter-LL scattering. The breakdown is ultimately limited by collective excitations in a regime where phonon and impurity scattering are quenched. The breakdown mechanism can be described by a Landau critical velocity as it bears strong similarities with the roton mechanism of superfluids. In addition, we show that breakdown is a precursor of an electric-field induced QHE-metal transition.

We theoretically study noncoplanar spin textures in polar magnetic conductors. Starting from the Kondo lattice model with the Rashba spin-orbit coupling, we derive an effective spin model with generalized Ruderman-Kittel-Kasuya-Yosida interactions including the anisotropic and antisymmetric exchange interactions. By performing simulated annealing for the effective model, we find that a vortex crystal of Néel type is stabilized even in the absence of a magnetic field. Moreover, we demonstrate that a Bloch-type vortex crystal, which is usually associated with the Dresselhaus spin-orbit coupling, can also be realized in our Rashba-based model. A magnetic field turns the vortex crystals into Néel- and Bloch-type Skyrmion-like crystals. Our results underscore that the interplay between the spin-orbit coupling and itinerant magnetism brings fertile possibilities of noncoplanar magnetic orderings.