We uncover a non-Hermitian skin mode in which the eigenmodes of a nonreciprocal topoelectrical (TE) heterojunction circuit array are localized at the heterojunction interface under both open boundary condition (OBC) and periodic boundary condition (PBC). This is in marked contrast to the conventional non-Hermitian skin effect (NHSE) in homogenous non-Hermitian systems that exists under OBC but vanishes in PBC. The interfacial non-Hermitian skin effect is induced when two non-Hermitian circuit chain segments with dissimilar NHSE decay lengths are cascaded together. It is shown analytically that the interfacial NHSE decay rates are directly associated with the asymmetric intracell couplings in the TE segments. Such nonreciprocal directional couplings can be realized in practical circuits by means of negative impedance converters with current inversion (INIC). In contrast to the conventional NHSE in homogeneous systems, the TE heterojunction circuit allows for a voltage profile localized at the interface, that is independent of the boundary conditions and whose decay length can be modulated by circuit parameters. Finally, the results presented are general and applicable to other analogous non-Hermitian platforms such as photonic and condensed matter nanoscale systems.

Laser-driven carbon ion beams from a carbon foil target via a 2.5-J laser pulse are investigated with three-dimensional particle-in-cell simulations. An ion bunch with a narrow energy range exhibits a thin shell shape with a certain diameter. The ion cloud has a layered structure of these ion bunches with different energies. The divergences of the ion bunch in the laser inclination direction and perpendicular to it are different in an oblique incidence laser. In addition, theoretical formulas for the radius of the generated ion beam and the energy spectrum are derived, and they are shown to be in good agreement with the simulation results.

The Heisenberg antiferromagnet on the kagome lattice is an archetypal instance of how large ground-state degeneracies arise, and how they may get resolved by thermal and quantum fluctuations. Augmenting the Heisenberg model by chiral spin interactions has proved to be of particular interest in the discovery of certain chiral quantum spin liquids. Here we consider the classical variant of this chiral kagome model and find that it exhibits, similar to the classical Heisenberg antiferromagnet, a remarkably large and structured ground-state manifold, which combines continuous and discrete degrees of freedom. This allows for a rich set of order-by-disorder phenomena. Degeneracy lifting occurs in a highly selective way, choosing already at the harmonic level specific triaxial states, which however retain an emergent ${\mathbb{Z}}_2$ degree of freedom (absent in the conventional Heisenberg model). We also study the competition of entropic and energetic ground-state selection as the model interpolates between the purely chiral and Heisenberg cases. For this mixed model, we find a “proximate ordered-by-disorder” finite-temperature regime where fluctuations overcome the energetic ground-state preference of the perturbation. Finally, a semiclassical route to a spin liquid is provided by quantum order by disorder in the purely chiral models, where the aforementioned ${\mathbb{Z}}_2$ degrees of freedom are elevated to the role of an emergent gauge field.

We systematically investigate the ground-state properties of self-bound droplets of quasi-two-dimensional binary Bose gases by using the Gaussian state theory. We find that quantum droplets consists of two macroscopic squeezed phases and a macroscopic coherent phase. We map out the phase diagram and determine all phase boundaries via both numerical and nearly analytical methods. In particular, we find three easily accessible signatures for the quantum phases and the stabilization mechanism of the self-bound droplets by precisely measuring their radial size. Our studies indicate that binary droplets represent an ideal platform for in-depth investigations of the quantum nature of the droplet state.

We study the collective dynamical behavior of active particles with topological interactions and directional reversals. Surprising phenomena are shown to emerge as the interaction relaxation time is varied relative to the reversal rate, such as the spontaneous formation of collective chiral states and collective flow reversals in the presence of confinement. The results have a direct relevance to modeling and understanding collective reversals in active matter.

In this study we characterize the tautomerization of HPc on Cu(111) as a charge-carrier-induced reversible one-electron process. An analysis of the bias-dependent tautomerization rate finds an energy threshold that corresponds to the energy of the N-H stretching mode. By using the tautomerization of the molecule as a detector for charge carrier transport in the so-called molecular nanoprobe (MONA) technique, we provide evidence for an inhomogeneous coupling between the fourfold-symmetric molecule and sixfold-symmetric surface. We conclude the study by comparing the energy dependence of charge carrier transport on the Cu(111) to the Ag(111) surface. While the MONA technique is limited to the detection of hot-electron transport for Ag(111), our data reveal that the lower onset energy of the Cu surface state also allows for the detection of hot-hole transport. The influence of surface and bulk transport on the MONA technique is discussed.

We carried out a comprehensive high-resolution angle-resolved photoemission spectroscopy (ARPES) study of the pseudogap interplay with superconductivity in La-based cuprates. The three systems ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4, {\mathrm{La}}_{1.6-x}{\mathrm{Nd}}_{0.4}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$, and ${\mathrm{La}}_{1.8-x}{\mathrm{Eu}}_{0.2}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$ display slightly different pseudogap critical points in the temperature versus doping phase diagram. We studied the pseudogap evolution into the superconducting state for doping concentrations just below the critical point. In this setting, near optimal doping for superconductivity and in the presence of the weakest possible pseudogap, we uncover how the pseudogap is partially suppressed inside the superconducting state. This conclusion is based on the direct observation of a reduced pseudogap energy scale and re-emergence of spectral weight suppressed by the pseudogap. Altogether these observations suggest that the pseudogap phenomenon in La-based cuprates is in competition with superconductivity for antinodal spectral weight.

We show that the optical spin conductivity, which is a small ac response of a bulk spin current and elusive in condensed matter systems, can be measured in ultracold atoms. We demonstrate that this conductivity contains rich information on quantum states by analyzing experimentally achievable systems such as a spin-$\frac{1}{2}$ superfluid Fermi gas, a spin-1 Bose-Einstein condensate, and a Tomonaga-Luttinger liquid. The obtained conductivity spectra, which are absent in the Drude conductivity, reflect quasiparticle excitations and non-Fermi-liquid properties. Accessible physical quantities include the superfluid gap and the contact for the superfluid Fermi gas, gapped and gapless spin excitations as well as quantum depletion for the Bose-Einstein condensate, and the spin part of the Tomonaga-Luttinger liquid parameter elusive in cold-atom experiments. Unlike its mass transport counterpart, the spin conductivity serves as a probe applicable to clean atomic gases without disorder or lattice potentials. Our formalism can be generalized to various systems such as spin-orbit-coupled and nonequilibrium systems.

We use a first-passage time approach to study the statistics of the trapping times induced by persistent motion of active particles colliding with flat boundaries. The angular first-passage time distribution and mean first-passage time are calculated exactly for active Brownian and run-and-tumble particles, and the results of the two prototypes of active particles are contrasted. Theoretical predictions are in excellent agreement with Langevin simulations of active particle dynamics. Our results shed further light on how active particles with different dynamics may have equivalent statistical properties in the bulk yet behave differently near boundaries or obstacles.

Many-body Green's functions encode all the properties and excitations of interacting electrons. While these are challenging to be evaluated accurately on a classical computer, recent efforts have been directed toward finding quantum algorithms that may provide a quantum advantage for this task, exploiting architectures that will become available in the near future. In this work we introduce a novel near-term quantum algorithm for computing one-particle Green's functions via their Lehmann representation. The method is based on a generalization of the quantum equation of motion algorithm that gives access to the charged excitations of the system. We demonstrate the validity of the present proposal by computing the Green's function of a two-site Fermi-Hubbard model on a IBM quantum processor.

We analyze the problem of resolving two mutually coherent point sources with arbitrary quantum statistics, mutual phase, and relative and absolute intensity. We use a sensitivity measure based on the method of moments and compare direct imaging with spatial-mode demultiplexing (SPADE), analytically proving advantage of the latter. We show that the moment-based sensitivity of SPADE saturates the quantum Fisher information for all known cases, even for non-Gaussian states of the sources.

The study of dynamical phase transitions has been attracting considerable research efforts in the last decade. One theme of present interest is to search for exotic scenarios beyond the framework of equilibrium phase transitions. Here, we establish a duality between many-body dynamics and static Hamiltonian ground states for both classical and quantum systems. We construct frustration-free Hamiltonians whose ground-state phase transitions have rigorous duality to chaotic transitions in dynamical systems. By this duality, we show that the corresponding ground-state phase transitions are characterized by a bulk-to-surface response; these phase transitions are then dubbed “peratic,” meaning that they are defined by their response to the boundary. For the classical system, we show how the timelike dimension emerges in the static ground states. For the quantum system, the ground state is a superposition of geometrical lines on a two-dimensional array; these lines encode the dynamical Floquet evolution history of one-dimensional disordered spin chains. Our prediction of a peratic phase transition has direct consequences in quantum simulation platforms such as Rydberg atoms and superconducting qubits, as well as anisotropic spin glass materials. The discovery would shed light on the unification of dynamical phase transitions with equilibrium systems.

We present a de Haas–van Alphen quantum oscillation study of the Dirac nodal-line semimetal HfSiS up to 32 T to unravel the structure of the high-frequency magnetic breakdown spectrum that was previously obscured in transport experiments. Despite a threefold enhanced gap between adjacent electron and hole pockets relative to the sister compound ZrSiS, a large number of large-area magnetic breakdown orbits enclosing the nodal-loop are identified. All breakdown orbits are assigned by extracting their cyclotron masses. Moreover, one additional low-frequency magnetic breakdown orbit, previously absent in ZrSiS, is observed and attributed to the larger spin-orbit interaction in HfSiS.

The advent of noisy-intermediate scale quantum computers has introduced the exciting possibility of achieving quantum speedups in machine learning tasks. These devices, however, are composed of a small number of qubits and can faithfully run only short circuits. This puts many proposed approaches for quantum machine learning beyond currently available devices. We address the problem of compressing classical data into efficient representations on quantum devices. Our proposed methods allow both the required number of qubits and depth of the quantum circuit to be tuned. We achieve this by using a correspondence between matrix-product states and quantum circuits and further propose a hardware-efficient quantum circuit approach, which we benchmark on the Fashion-MNIST dataset. Finally, we demonstrate that a quantum circuit-based classifier can achieve competitive accuracy with current tensor learning methods using only 11 qubits.

We construct a family of three-body spin-$\frac{1}{2}$ Hamiltonians with a superextensive set of infinitely long-lived multimagnon states. A magnon in each such state carries either quasimomentum zero or fixed $p_0\ne 0$, and energy $\mathrm{\Omega }$. These multimagnon states provide an archetypal example of quantum many-body scars: they are eigenstates at finite-energy density that violate the eigenstate thermalization hypothesis, and lead to persistent oscillations in local observables in certain quench experiments. On the technical side, we demonstrate the systematic derivation of scarred Hamiltonians that satisfy a restricted spectrum-generating algebra using an operator basis built out of irreducible tensor operators. This operator basis can be constructed for any spin, spatial dimension, or continuous non-Abelian symmetry that generates the scarred subspace.