The interaction between solid materials and an optical vortex has garnered significant attention in recent years. Here, we study theoretically the high-order harmonic generation (HHG) of crystalline solids under the spatiotemporal optical-vortex light. We develop a quantum-orbit model to describe the intricate electron motion driven by a strong optical vortex, demonstrating the conservation law of spin and transverse orbital angular momenta in the HHG process. Harnessing the bicircular spatiotemporal vortex light field, we generate high-order harmonics with the hybrid spin and transverse orbital angular momentum. The proportions of different orbital angular-momentum components of harmonics in solids can also be tuned by adjusting the intensity ratio of the two light beams.

We theoretically investigate the topological edge-state impact on high-order harmonic generation (HHG) in solids, with a focus on the modification of the topological edge-state dynamics by spatially structured (SS) light. Our findings reveal an underlying mechanism coupling the spatial inhomogeneity of light with the topological states, which leads to a notable but counterintuitive enhancement of HHG yields by SS light, even with a lower average field-intensity compared to the conventional spatially homogeneous light. We attribute this giant coupling effect to the dynamical modulation of the energy bands by the SS light in the HHG process, building an “electron lift” scenario of the topological edge states. Our study not only highlights the intricate interplay between spatial inhomogeneity of laser fields and topological condensed matter but also paves pathways for manipulating electron dynamics in solids using the unique properties of SS light.

We calculate the properties of a one-dimensional $Z_2$ lattice gauge theory in different Gauss-law sectors, corresponding to different configurations of static charges, set by the orientations of the gauge spins. Importantly, in quantum simulator experiments these sectors can be accessed without adding any additional physical particles or changing the Hamiltonian: the Gauss-law sectors are simply set by the initial conditions. We study the interplay between conservation laws and interactions when the static charges are chosen to form periodic patterns. We classify the different Gauss-law sectors and use the density matrix renormalization group to calculate the ground-state compressibility, density profiles, charge-density-wave order parameters, and single-particle correlation functions as a function of matter density. We find confined and deconfined phases, charge density waves, correlated insulators, and supersolids.

We study the superfluid–Bose-glass transition in a one-dimensional lattice boson model with power-law decaying hopping amplitude $t_{i-j}\sim 1/{|i-j|}^{\alpha }$, using bosonization and the nonperturbative functional renormalization group (FRG). When $\alpha$ is smaller than a critical value ${\alpha }_c<3$, the U(1) symmetry is spontaneously broken, which leads to a density mode with nonlinear dispersion and dynamical exponent $z=(\alpha -1)/2$; the superfluid phase is then stable for sufficiently weak disorder, contrary to the case of short-range hopping where disorder is a relevant perturbation when the Luttinger parameter is smaller than $3/2$. In the presence of disorder, however, long-range hopping has no effect in the infrared limit and the FRG flow eventually becomes similar to that of a boson system with short-range hopping. This implies that the superfluid phase, when stable, exhibits a density mode with linear dispersion ($z=1$) and the superfluid–Bose-glass transition remains in the Berezinskii-Kosterlitz-Thouless universality class, while the Bose-glass fixed point is insensitive to long-range hopping. We compare our findings with a recent numerical study.

Quantum simulation of a monopole-spin hybrid system is performed on the basis of a dipolar ultracold gas in a ladder lattice. The site-occupation states of the dipolar ladder lattice gas can spontaneously emulate both the monopole and spin excitations. The hopping of the atoms induces a particle conversion process between spin and monopole pairs, and the dipole-dipole interaction determines the spin-spin, spin-monopole, and monopole-monopole interactions. The anisotropic nature of the dipole-dipole interaction allows hereby for a flexible engineering of the designed hybrid system, and for a significant tunability of the interaction strengths. As a result, we encounter a rich phase diagram, and specifically a self-assembled Coulomb phase arises, in which monopoles and spins coexist and are orderly arranged according to the local Gauss's law. The Coulomb phase hosts a zoo of different types of quasiparticles and provides the possibility to simulate various phenomena in particle physics, such as a degenerate vacuum, particle decay, and conversion processes. Our work provides a significant extension of the scope of quantum simulations based on the anisotropy of dipolar interactions.

We unravel stationary states in the form of dark soliton stripes, bubbles, and kinks embedded in a two-dimensional droplet-bearing setting emulated by an extended Gross-Pitaevskii approach. The existence of these configurations is corroborated through an effectively reduced potential picture demonstrating their concrete parametric regions of existence. The excitation spectra of such configurations are analyzed within the Bogoliubov–de Gennes framework exposing the destabilization of dark soliton stripes and bubbles, while confirming the stability of droplets, and importantly unveiling spectral stability of the kink against transverse excitations. Additionally, a variational approach is constructed providing access to the transverse stability analysis of the dark soliton stripe for arbitrary chemical potentials and widths of the structure. This is subsequently compared with the stability analysis outcome demonstrating very good agreement at small wave numbers. Dynamical destabilization of dark soliton stripes via the snake instability is showcased, while bubbles are found to feature both a splitting into a gray soliton pair and a transverse instability thereof. These results shed light on unexplored stability and instability properties of nonlinear excitations in environments featuring a competition of mean-field repulsion and beyond-mean-field attraction that can be probed by state-of-the-art experiments.

We investigate the scattering and two-body bound states of two ultracold atoms in a quasi-two-dimensional (quasi-2D) confinement, with the confinement potential being an infinitely deep square well (box potential) in the transverse ($z$) direction, and the motion of the atoms in the $x\text{−}y$ plane being free. Specifically, we calculate the effective 2D scattering length and 2D effective range parameter of the low-energy scattering, as well as the energy and the transverse-excited-mode probability of the bound states. Comparing these results with those obtained under a harmonic transverse confinement potential, which has the same characteristic length as the box potential, we find that in most of the cases the 2D effective range parameter for the box confinement is approximately 0.28 of the one for the harmonic confinement. Moreover, the transverse-excited-mode probability of the bound states for the box confinement is also much lower than the one for the harmonic confinement. These results suggest that the transverse excitation in the box confinement is notably weaker than the one in the harmonic confinement with the same characteristic length. Therefore, achieving quasi-2D ultracold gases well described by pure-2D effective models, particularly those with 2D contact interaction, is more feasible through box confinement. Our results are helpful for the quantum simulation of 2D many-body physics with ultracold atoms, e.g., the suppression of 2D effective range parameter may lead to an enhancement of quantum anomaly in two-dimensional Fermi gases. Additionally, our calculation method is applicable to the two-body problems of ultracold atoms in other types of quasi-2D confinements.

In this article, we demonstrate dense resonant peaks in the transmission spectra of a rectangular waveguide inscribed with a stretched moiré pattern. We investigated an array of silicon waveguides with sinusoidally modulated cladding of varying depth of modulation. The investigation reveals a critical depth of modulation that splits the geometries into weakly scattering and strongly scattering regimes. Geometries in the weakly scattering regime resemble Bragg waveguides with shallow cladding modulation, whereas in the strongly scattering regime, the geometries resemble chains of isolated dielectric particles. The guided mode photonic band gap for geometries in the strongly scattering regime is much larger than that of the weakly scattering regime. By inscribing stretched moiré patterns in the strongly scattering regime, we show that a large number of sharp peaks can be created in the transmission spectra of the waveguide. All periodic stretched moiré patterns can be identified with an R parameter. The R parameter indicates the ratio of the supercell period of the stretched system to the unstretched system. Our empirical study shows that the density of peaks linearly increases with R. The multiple resonance peaks evolve along well-defined trajectories with the quality factor defined by exponential functions of R.

We investigate the microwave-field-induced cross-phase modulation in a room-temperature coherently driven five-level inverted-Y-type system. By solving the optical Bloch equations via the Fourier transformation, we derive two nonlinearly coupled envelope equations governing the dynamics of left- and right-polarized components of a linearly polarized probe field. Under the weak probe field approximation, we show that the cross-phase modulation-induced phase difference between two components of the probe field is approximately proportional to the microwave field intensity. By choosing a specified probe field frequency, the group velocities for the left- and right-polarized components of the probe field match perfectly so that the phase difference can be detected at the end of the medium, enabling the undistorted detection of the microwave field. Considering the square-pulsed microwave field with a 50% duty cycle, we also demonstrate microwave communication by detecting the cross-phase modulation-induced phase difference.

We present analytic expressions for the coincidence detection probability amplitudes of photon pairs generated by spontaneous parametric down-conversion in both momentum and position spaces, without using the Gaussian approximation and taking into account the effects of birefringence in the nonlinear crystal. We also present experimental data supporting our theoretical predictions, using Einstein-Podolsky-Rosen correlations as benchmarks, for eight different pump beam configurations.

We present a method aimed at protecting unitary dynamics in the presence of decoherence, by integrating leakage elimination operators (LEOs) into the system's evolution to create dynamical leakage-free paths. Deriving the dynamical equation for an open quantum system with general drives can be challenging. Our approach avoids the rotating wave approximation and instead uses the coarse-grained averaging technique to derive a quantum master equation for such systems. The combination of the coarse-graining approach and LEO operators appears suitable to study Markovian control methods. We show that employing LEO pulses in specific subspaces can reduce errors arising from undesired transitions due to decoherence. Notably, satisfactory final fidelity can still be achieved even when the reservoir is at a finite temperature. By looking into the dynamical equation governing the quantum state on the dynamical leakage-free path, we provide analytical insights into the effectiveness of the LEO method in suppressing decoherence effects.

We discuss the behavior of positive linear maps in fermionic systems and then propose the phase partial transpose and the phase entanglement negativity. We show that every fermionic state which mixes local fermion-number parity must have nonvanishing nontrivial phase entanglement negativity, which gives an affirmative answer to a conjecture proposed by Shapourian and Ryu [Phys. Rev. A 99, 022310 (2019)]. In addition, we prove that the phase entanglement negativity is an entanglement monotone and establish some equalities and inequalities related to the phase entanglement negativity which, particularly, provide some upper bounds and lower bounds of the fermionic entanglement negativity. A more detailed discussion of the $(1+M)$-mode case is also presented, and our results generalize some known findings.

We discuss adiabatic spectra and dynamics of the quantum, i.e., transverse field, Hopfield model with dilute memories (the number of stored patterns, $p<{log}_{2}N$, where $N$ is the number of qubits). At some critical transverse field, the model undergoes the quantum phase transition from the ordered to the paramagnetic state. The corresponding critical exponents are calculated and used to determine the efficiency of quantum annealing protocols. We also discuss implications of these results for the quantum annealing of generic spin glass models.

Advanced quantum networking systems rely on efficient quantum error correction codes for their optimal realization. The rate at which the encoded information is transmitted is a fundamental limit that affects the performance of such systems. Quantum aggregation allows one to increase the transmission rate by adding multiple paths connecting two distant users. Aggregating channels of different paths allows more users to simultaneously exchange the encoded information. Recent work has shown that quantum aggregation can also reduce the number of physical resources of an error correction code when it is combined with the quantum multiplexing technique. However, the difference in channel lengths across the various paths means some of the encoded quantum information will arrive earlier than others and it must be stored in quantum memories. The information stored will then deteriorate due to decoherence processes leading to detrimental effects for the fidelity of the final quantum state. Here, we explore the effects of a depolarization channel that occurs for the quantum Reed-Solomon code when quantum aggregation involving different channel lengths is used. We determine the best distribution of resources among the various channels connecting two remote users. Furthermore, we estimate the coherence time required to achieve a certain fidelity. Our results will have a significant impact on the ways physical resources are distributed across a quantum network.

In the realm of quantum control, reinforcement learning, a prominent branch of machine learning, emerges as a competitive candidate for computer-assisted optimal experiment design. This paper investigates the extent to which guidance from human experts is necessary for effectively implementing reinforcement learning in the design of quantum control protocols. Specifically, our focus lies on engineering a robust two-qubit gate, utilizing a combination of analytical solutions as prior knowledge and techniques from computer science. Through thorough benchmarking of various models, we identify dropout—a widely used method for mitigating overfitting in machine learning—as a particularly robust approach. Our findings demonstrate the potential of integrating computer science concepts to propel the development of advanced quantum technologies.

We numerically and analytically study ionization of ${\mathrm{H}}_2{}^{+}$ with large internuclear distances $R$ in strong elliptically polarized laser fields. Numerical simulations show that the offset angle in the photoelectron momentum distribution (PMD) is larger for cases of large $R$ than for cases of ${\mathrm{H}}_2{}^{+}$ with small $R$ and model atoms with similar ionization potentials. In addition, the PMDs for cases of large $R$ show clear interference patterns which disappear for cases of small $R$. By developing a strong-field model which includes the contributions of the first excited state and the Coulomb potential, we reproduce the phenomena for large $R$. Tunneling ionization of ${\mathrm{H}}_2{}^{+}$ with large $R$ involves a complex four-body interaction between the laser, the electron, and the two nuclei. Our model can approximate the four-body interaction as the three-body one and clearly identify the effects of charge resonance and different nuclei on tunneling ionization. Our work suggests a manner for probing complex interactions in strong-field ionization of stretched molecules with high time resolution.

The theory of molecular Siegert states in a static electric field in the zero-range potential model is developed. The model admits extended analytical and accurate numerical treatments, which enables one to study tunneling ionization of large polyatomic molecules with complex geometry in strong fields beyond the weak-field approximation. The theory is illustrated by calculations for three model molecules reproducing the geometry of the real water, benzene, and leucine molecules. The field and orientation dependence of two major ionization observables, the ionization rate and the transverse momentum distribution of liberated electrons, is analyzed. The calculations reveal a number of strong-field effects not accounted for by the weak-field asymptotic theory. In particular, it is shown that vortex electrons are efficiently generated in tunneling ionization of large molecules at sufficiently strong fields, which opens a perspective for enantiosensitive rescattering photoelectron spectroscopy. The mechanism of tunneling-induced electron diffraction and its manifestation in the transverse momentum distribution are discussed.

Spin-orbit dynamics and relativistic corrections to the kinetic energy in strong-field dynamics have long been ignored for near- and mid-infrared fields with intensities ${10}^{13}\text{–}{10}^{14}\mathrm{W}/{\mathrm{cm}}^2$, as the final photoelectron energies are considered too low for these effects to play a role. However, using a precise and flexible path-integral formalism, we include all correction terms from the fine-structure, Breit-Pauli Hamiltonian. This enables a treatment of spin, through coherent spin states, which is the first model to use this approach in strong-field physics. We are able to show that the most energetically rescattered wave packets are effected by relativistic kinetic energy corrections during rescattering. We probe these effects and show that they yield notable differences for a 1600-nm wavelength laser field on the dynamics and the photoelectron spectra. Furthermore, we find that the dynamical spin-orbit coupling is strongly overestimated if relativistic corrections to kinetic energy are not considered. Finally, we derive a new condition that demonstrates that relativistic effects begin to play a role at intensities many orders of magnitude lower than expected for the case of rescatterering. Our findings may have important implications for imaging processes such as laser-induced electron diffraction, which includes high-energy photoelectron recollisions.

It is widely appreciated, due to Bell's theorem, that quantum phenomena are inconsistent with local-realist models. In this context, locality refers to local causality, and there is thus an open possibility for reproducing the quantum predictions with models which internally violate the causal arrow of time, while otherwise adhering to the relevant locality condition. So far, this possibility has been demonstrated only at a toy-model level, and only for systems involving one or two spins (or photons). The present work extends one of these models to quantum correlations between three or more spins which are entangled in the Greenberger-Horne-Zeilinger state.

A recently developed approach to the thermodynamics of open quantum systems, on the basis of the principle of minimal dissipation, is applied to the spin-boson model. Employing a numerically exact quantum dynamical treatment based on the hierarchical equations of motion (HEOM) method, we investigate the influence of the environment on quantities such as work, heat, and entropy production in a range of parameters which go beyond the weak-coupling limit and include both the nonadiabatic and the adiabatic regimes. The results reveal significant differences to the weak-coupling forms of work, heat, and entropy production, which are analyzed in some detail.