We present a computational study based on density functional plus dynamical mean-field theory calculations for the normal-state electronic reconstruction of pure and hole-doped ${\mathrm{NdNiO}}_2$ superconductors. Our results capture the $T$ dependence of the electrical resistivity, providing a many-particle interpretation of the emergence of pseudogaplike features at low energies as well as the weakly insulating regime seen in experiment. We show how Mottness manifests itself in the weak localization to bad-metallicity crossover due to strong correlation in the $e_g$-shell one-particle spectral functions and self-energies.

Devising optimal interventions for constraining stochastic systems is a challenging endeavor that has to confront the interplay between randomness and dynamical nonlinearity. Existing intervention methods that employ stochastic path sampling scale poorly with increasing system dimension and are slow to converge. Here we propose a generally applicable and practically feasible methodology that computes the optimal interventions in a noniterative scheme. We formulate the optimal dynamical adjustments in terms of deterministically sampled probability flows approximated by an interacting particle system. Applied to several biologically inspired models, we demonstrate that our method provides the necessary optimal controls in settings with terminal, transient, or generalized collective state constraints and arbitrary system dynamics.

Twisted bilayer graphene (TBG) near “magic angles” has emerged as a rich platform for strongly correlated states of two-dimensional (2D) Dirac semimetals. Here we show that twisted bilayers of thin film magnetic topological insulators (MTIs) with large in-plane magnetization can realize flat bands near 2D Dirac nodes. Using a simple model for thin films of MTIs, we derive a continuum model for two such MTIs, twisted by a small angle with respect to each other. When the magnetization is in plane, we show that interlayer tunneling terms act as effective SU(2) vector potentials, which are known to lead to flat bands in TBG. We show that by changing the in-plane magnetization, it is possible to tune the twisted bilayer MTI band dispersion to quadratic band touching or to flat bands, similar to the TBG. If realized, this system can be a highly tunable platform for strongly correlated phases of two-dimensional Dirac semimetals.

We introduce a practical hybrid approach that combines orbital-free density functional theory (DFT) with Kohn-Sham DFT for speeding up first-principles molecular dynamics simulations. Equilibrated ionic configurations are generated using orbital-free DFT for subsequent Kohn-Sham DFT molecular dynamics. This leads to a massive reduction of the simulation time without any sacrifice in accuracy. We assess this finding across systems of different sizes and temperature, up to the warm dense matter regime. To that end, we use the cosine distance between the time series of radial distribution functions representing the ionic configurations. Likewise, we show that the equilibrated ionic configurations from this hybrid approach significantly enhance the accuracy of machine-learning models that replace Kohn-Sham DFT. Our hybrid scheme enables systematic first-principles simulations of warm dense matter that are otherwise hampered by the large numbers of atoms and the prevalent high temperatures. Moreover, our finding provides an additional motivation for developing kinetic and noninteracting free-energy functionals for orbital-free DFT.

Genuinely two-dimensional robust crosscurrents—which flow against the natural direction of heat flux— have been missing since the discovery of their one-dimensional counterpart. We provide a setup to realize them on a cubic three-dimensional (3D) lattice hosting a Hofstadter model coupled to two heat baths with different temperatures. We show that these currents exhibit dissipative robustness; they are stable against the presence of impurities and tilting of the gauge field in certain nonequilibrium configurations. Moreover, we find protected boundary currents with genuinely 3D robustness, i.e., they are only stable if tunneling can occur in all three spatial directions. The model also presents generic surface currents, which are robust for both bosonic and fermionic systems. We identify the underlying qualitative mechanism responsible for the robustness of the surface currents and the crucial role played by certain discrete symmetries.

We use machine learning to classify rational two-dimensional conformal field theories (CFTs). We first use the energy spectra of these minimal models to train a supervised learning algorithm. In contrast to conventional methods that are typically qualitative and also involve system size scaling, our method quantifies the similarity of the spectrum of a system at a fixed size to candidate CFTs. Such an approach allows us to correctly predict the nature and the value of critical points of several strongly correlated spin models using only their energy spectra. Our results are also relevant for the ground-state entanglement Hamiltonian of certain topological phases of matter, described by CFTs. Remarkably, we achieve high prediction accuracy by only using the lowest few Réyni entropies as the input. Finally, using autoencoders, an unsupervised learning algorithm, we find a hidden variable that has a direct correlation with the central charge and discuss prospects for using machine learning to investigate other conformal field theories, including higher-dimensional ones.

In this paper, we present evidence of directional wave behavior, i.e., beaming and diffraction, along high-order rotational symmetries of quasicrystalline elastic metamaterial plates. These structures are obtained by placing pillars on an elastic plate following a particular rotational symmetry arrangement, such as eightfold and tenfold rotational symmetries, as enforced by a design procedure in reciprocal space. We estimate the dispersion properties of the waves propagating in the plates through Fourier transformation of transient wave fields. The procedure identifies, both numerically and experimentally, the existence of anisotropic bands characterized by high-energy density at isolated zones in reciprocal space that follow their higher order rotational symmetry. Specific directional behavior is showcased at the identified frequency bands, such as wave beaming (predicted in simulations and confirmed experimentally) and diffraction (exemplified only with numerical results). This paper expands the wave directionality phenomena beyond the symmetries of periodic configurations (e.g., fourfold and sixfold), and opens possibilities for applications involving the unusual high-order wave features of the quasicrystals (e.g., eightfold and tenfold) such as superior guiding, focusing, sensing, and imaging.

We report neutron depolarization measurements of the suppression of long-range ferromagnetism and the concomitant emergence of magnetic irreversibilities and spin freezing in ${\mathrm{CePd}}_{1-x}{\mathrm{Rh}}_x$ around $x^{*}\approx 0.6$. Tracking the temperature versus field history of the neutron depolarization, we find clear signatures of long-range Ising ferromagnetism below a Curie temperature $T_{\mathrm{C}}$ for $x=0.4$ and a spin freezing of ferromagnetic clusters below a freezing temperature $T_{\mathrm{F}1}$ for $x>x^{*}$. Under zero-field-cooling/field-heating and for $x>x^{*}$ a reentrant temperature dependence of the neutron depolarization between $T_{\mathrm{F}2}<T_{\mathrm{F}1}$ and $T_{\mathrm{F}1}$ is microscopically consistent with a thermally activated growth of the cluster size. The evolution of the depolarization as well as the reentrant temperature dependence as a function of Rh content are consistent with the formation of a Kondo cluster glass below $T_{\mathrm{F}1}$ adjacent to a ferromagnetic quantum phase transition at $x^{*}$.

The role of Rydberg autoionizing states in interfering one- and two-photon ionization paths is theoretically investigated in atomic Ar. The angularly resolved photoionization cross sections for each individual path is provided. By varying the relative optical phase between the two pulses the phase difference between the two interfering paths is extracted. The retrieved phase difference and the photoelectron angular distributions exhibit a strong dependence on the photon energy in the vicinity of the resonant states. In contrast to previous results obtained in atomic Ne, the phase difference features a smooth dependence with photoelectron emission angle.

Quantum many-body scars are an intriguing dynamical regime in which quantum systems exhibit coherent dynamics and long-range correlations when prepared in certain initial states. We use this combination of coherence and many-body correlations to benchmark the performance of present-day quantum computing devices by using them to simulate the dynamics of an antiferromagnetic initial state in mixed-field Ising chains of up to 19 sites. In addition to calculating the dynamics of local observables, we also calculate the Loschmidt echo and a nontrivial unequal-time connected correlation function that witnesses long-range many-body correlations in the scarred dynamics. We find coherent dynamics to persist over up to 40 Trotter steps even in the presence of various sources of error. To obtain these results, we leverage a variety of error-mitigation techniques including noise tailoring, zero-noise extrapolation, dynamical decoupling, and physically motivated postselection of measurement results. Crucially, we also find that using pulse-level control to implement the Ising interaction yields a substantial improvement over the standard controlled-not-based compilation of this interaction. Our results demonstrate the power of error-mitigation techniques and pulse-level control to probe many-body coherence and correlation effects on present-day quantum hardware.

Elastoplastic lattice models for the response of solids to large-scale deformation typically incorporate structure only implicitly via a local yield strain that is assigned to each site. However, the local yield strain can change in response to a nearby or even distant plastic event in the system. This interplay is key to understanding phenomena such as avalanches in which one plastic event can trigger another, leading to a cascade of events, but is typically neglected in elastoplastic models. To include the interplay one could calculate the local yield strain for a given particulate system and follow its evolution, but this is expensive and requires knowledge of particle interactions that aren't necessarily pairwise additive or possible to extract from experiments. Instead, we use a structural quantity, “softness,” obtained using machine learning to correlate with imminent plastic rearrangements. We show that softness correlates with local yield strain and use it to construct a “structuro-elasto-plasticity” model that reproduces particle simulation results reasonably well for several observable quantities, confirming that we capture the influence of the interplay of local structure, plasticity, and elasticity on material response.

Precise control of the filamentation of an ultrashort and intense near-infrared laser pulse in air is crucial for many applications but remains challenging. By combining inverse design for shaping of a pulse at the output of a laser with simulation of the nonlinear propagation of the pulse in air, we numerically investigate the way to simultaneously control the length and position of a plasma filament at an arbitrary remote distance for the first time. An intermediate state, with a Bessel-Gauss beam profile, is introduced between the laser output and the filament. Through forward and backward propagations of the intermediate state, an end-to-end design of the initial laser pulse is achieved to match the desired filament characteristics. Our calculations show that a properly engineered torus pulse can project such a Bessel-Gauss beam at remote distance and generate a long plasma filament without requiring any feedback loop. We also proposed an experimental arrangement to project such an intermediate state and generate the corresponding filament remotely. The method can be further extended to other types of filaments or targets that may be reached from different intermediate states.

The Kitaev model is an exactly solvable quantum spin model within the language of constrained real fermions. In spite of numerous studies for magnetic fields along special orientations, there is a limited amount of knowledge on the complete field-angle characterization, which can provide valuable information on the existence of fractionalized excitations. For this purpose, we first study the pure ferromagnetic and antiferromagnetic Kitaev models for arbitrary external magnetic field directions via a mean-field theory, showing that there are many topological phases with different (or zero) Chern numbers, depending on the magnetic field strength and orientations. However, a realistic description of the candidate Kitaev materials, within the edge-sharing octahedra paradigm, requires additional coupling terms, including a large off-diagonal term $\mathrm{\Gamma }$ along with possible anisotropic corrections ${\mathrm{\Gamma }}_p$. It is therefore not sufficient to rely on the topological properties of the bare Kitaev model as the basis for the observed thermal Hall-conductivity signals, and an understanding of these extended Kitaev models with a complete field response is demanded. Starting from the zero-field phase diagram of $\mathrm{K}\text{−}\mathrm{\Gamma }\text{−}{\mathrm{\Gamma }}_p$ models, we identify, besides the Kitaev spin liquid phase, antiferromagnetic zigzag, ferromagnetic phases, as well as an unusual Kitaev(-$\mathrm{\Gamma }$) spin liquid phase. The magnetic field response of these phases for arbitrary field orientations provides a remarkably rich phase diagram. For an extended parameter range and just above the critical field where the zigzag phase is suppressed, there is an intermediate phase region with suppressed energy gaps and substantial spin fractionalization. To comply our findings with experiments, we also reproduce a large asymmetry in the extent of this intermediate phases specifically for the two different field directions $\theta =\pm {60}^o$ with respect to the normal to the plane of the honeycomb lattice.

The Schrieffer-Wolff transformation aims to solve degenerate perturbation problems and give an effective Hamiltonian that describes the low-energy dynamics of the exact Hamiltonian in the low-energy subspace of an unperturbed Hamiltonian. This unitary transformation decoupling the low-energy and high-energy subspaces for the transformed Hamiltonian can be realized by quantum circuits. We give a fully quantum algorithm for realizing the SW transformation. We also propose a hybrid quantum-classical algorithm for finding the effective Hamiltonian on NISQ hardware, where a general cost function is used to indicate the decoupling degree. Numerical simulations without or with noise and experiments on quantum computer ibmq_manila are implemented for a Heisenberg chain model. Our results verify the algorithm and show its validity on near-term quantum computers.

We study the collective spontaneous emission of three identical two-level atoms initially prepared in the excited states by measuring Glauber's third-order photon correlation function. Assuming two atoms at subwavelength distance from each other such that they are subject to the dipole-dipole interaction while the third one is located several wavelengths away, we observe super- and subradiant decay alike, depending on the direction of observation. Unlike the case where no remote atom is introduced or no conditional measurements are performed, the spontaneous emission behavior of the conditioned three-atom system is strongly modified, i.e., differing from the single-atom and the canonical two-atom configuration. The conditional measurements associated with the three-photon correlation function in combination with the dipole-dipole interaction between the adjacent atoms lead to quantum interference among the different decay channels allowing one to engineer the spontaneous emission in space and time.