We introduce a two-parameter approximate counter-diabatic term into the Hamiltonian of the transverse-field Ising model for quantum annealing to accelerate convergence to the solution, generalizing an existing single-parameter approach. The protocol is equivalent to unconventional diabatic control of the longitudinal and transverse fields in the transverse-field Ising model and thus makes it more feasible for experimental realization than an introduction of new terms such as nonstoquastic catalysts toward the same goal of performance enhancement. We test the idea for the $p$-spin model with $p=3$, which has a first-order quantum phase transition, and show that our two-parameter approach leads to significantly larger ground-state fidelity and lower residual energy than those by traditional quantum annealing and by the single-parameter method. We also find a scaling advantage in terms of the time-to-solution as a function of the system size in a certain range of parameters as compared to the traditional methods in the sense that an exponential time complexity is reduced to another exponential complexity with a smaller coefficient. Although the present method may not always lead to a drastic exponential speedup in difficult optimization problems, it is useful because of its versatility and applicability for any problem after a simple algebraic manipulation, in contrast to some other powerful prescriptions for acceleration such as nonstoquastic catalysts in which one should carefully study in advance if it works in a given problem and should identify a proper way to meticulously control the system parameters to achieve the goal, which is generally highly nontrivial.

As a series of work about “fractonic superfluids,” in this paper, we develop an exotic fractonic superfluid phase in $d$-dimensional space where subdimensional particles—their mobility is partially restricted—are condensed. The off-diagonal long range order (ODLRO) is investigated. To demonstrate, we consider “lineons”—a subdimensional particle whose mobility is free only in certain one-dimensional directions. We start with a $d$-component microscopic Hamiltonian model. The model respects a higher-rank symmetry such that both particle numbers of each component and angular charge moments are conserved quantities. By performing the Hartree-Fock-Bogoliubov approximation, we derive a set of Gross-Pitaevskii equations and a Bogoliubov–de Gennes (BdG) Hamiltonian, which leads to a description of both condensed components and unification of gapless phonons and gapped rotons. With the coherent-path-integral representation, we also derive the long-wavelength effective field theory of gapless Goldstone modes and analyze quantum fluctuations around classical ground states. The Euler-Lagrange equations and Noether charges/currents are also studied. In two spatial dimensions and higher, such an ODLRO stays stable against quantum fluctuations. Finally, we study vortex configurations. The higher-rank symmetry enforces a hierarchy of thermal vortex excitations whose structures are dominated by two guiding statements. Specially, we construct two types of vortex excitations, the conventional and dipole vortices. The latter carries a charge with dimension as a momentum. The two statements can be more generally applicable. Further perspectives are discussed.

We identified a highly ordered moiré lattice at the buried $\mathrm{SrTi}{\mathrm{O}}_3$ (STO)-(La,Sr)(Al,Ta)-oxide (LSAT) interface by high-resolution x-ray diffraction reciprocal space mapping. We found long-ranged ordered supercells of 106/107 unit cells of unstrained STO-LSAT caused by complete lattice relaxation through high-temperature annealing. Transmission electron microscopy images show that this periodicity is based on line dislocations at the interface region. The presence of such ordered superstructures in such widely used complex oxides sets the ideal conditions for moiré-tuned interfacial electronic modifications and ferroelectric supercrystallinity, opening the possibility for interface functionalities and impacting findings on vortex structured multilayers systems.

We investigate the nature of the magnetic excitations of a bilayer single-orbital Hubbard model in the intermediate-coupling regime. This model exhibits a quantum phase transition (QPT) between a paramagnetic (PM) and an insulating antiferromagnetic (AFM) phase at a critical value of the coupling strength. By using the random phase approximation, we show that the QPT is continuous when the PM state is a band insulator and that the corresponding quantum critical point (QCP) arises from the condensation of preformed excitons. These low-energy excitons re-emerge on the other side of the QCP as the transverse and longitudinal modes of the AFM state. In particular, the longitudinal mode remains sharp for the model parameters relevant to ${\mathrm{Sr}}_3{\mathrm{Ir}}_2{\mathrm{O}}_7$ because of the strong easy-axis anisotropy of this material.

In non-Hermitian scattering problems, the behavior of the transmission probability is very different from its Hermitian counterpart; it can exceed unity or even be divergent, since the non-Hermiticity can add or remove the probability to and from the scattering system. In the present paper, we consider the scattering problem of a $PT$-symmetric potential, and we find a counterintuitive behavior. In the usual $PT$-symmetric non-Hermitian system, we would typically find stationary semi-Hermitian dynamics in a regime of weak non-Hermiticity but observe instability once the non-Hermiticity goes beyond an exceptional point. Here, in contrast, the behavior of the transmission probability is strongly non-Hermitian in the regime of weak non-Hermiticity with divergent peaks, while it is superficially Hermitian in the regime of strong non-Hermiticity, recovering the conventional Fabry-Pérot-type peak structure. We show that the unitarity of the $S$-matrix is generally broken in both of the regimes, but is recovered in the limit of infinitely strong non-Hermiticity.

The adaptive immune system of vertebrates can detect, respond to, and memorize diverse pathogens from past experience. While the clonal selection of T helper (Th) cells is the simple and established mechanism to better recognize new pathogens, the question that still remains unexplored is how the Th cells can acquire better ways to bias the responses of immune cells for eliminating pathogens more efficiently by translating the recognized antigen information into regulatory signals. In this work, we address this problem by associating the adaptive immune network organized by the Th cells with reinforcement learning (RL). By employing recent advancements of network-based RL, we show that the Th immune network can acquire the association between antigen patterns of and the effective responses to pathogens. Moreover, the clonal selection as well as other intercellular interactions are derived as a learning rule of the network. We also demonstrate that the stationary clone-size distribution after learning shares characteristic features with those observed experimentally. Our theoretical framework may contribute to revising and renewing our understanding of adaptive immunity as a learning system.

Absorption of x-ray photons by atomic inner shells of light-element organics and biomolecules often leads to formation of dicationic electronic states and to molecular fragmentation. We investigated the x-ray-induced dissociation landscape of a representative medium-sized organic molecule, thiophene, by femtosecond x-ray pulses from the Super Photon Ring-8 GeV (SPring-8) Angstrom Compact Free-Electron Laser (SACLA). Holes, created in the sulfur $2p$ orbital by photoemission, were filled by the Auger process that created dicationic molecular states within a broad range of internal energies—a starting point particular to x-ray-induced dynamics. The evolution of the ionized molecules was monitored by a pump-probe experiment using a near-infrared (800 nm) laser pulse. Ion-ion coincidence and ion momentum analysis reveals enhanced yields of ionic fragments from multibody breakup of the ring, attributed to additional ionization of the highly excited fraction of the dicationic parent molecular states. The transient nature of the enhancement and its decay with about a 160-fs time constant indicate formation of an open-ring parent geometry and the statistical survival time of the parent species before the dissociation events. By probing specific Auger final states of transient, highly excited nature by near-infrared light, we demonstrate how pump-probe signatures can be related to the key features in dynamics during the early period of the x-ray-induced damage of organic molecules and biomolecules.

We investigate spontaneous emission from a quantum emitter located within the mode volume of a microring resonator that features chiral exceptional points. We show that this configuration offers enough degrees of freedom to exhibit a full control to either enhance or suppress the emission process. Particularly, we demonstrate that the Purcell factor can be enhanced by a factor of two beyond its value in an identical microring operating at a diabolic point. Our conclusions, which are derived using a non-Hermitian Hamiltonian formalism, are confirmed by employing full-wave simulations of realistic photonic structures and materials. Our results offer a straightforward route to improve the performance of single photon sources using current photonics technology without the need for building optical resonators with ultrahigh quality factors or nanoscale volumes.

When a chaotic, ergodic Hamiltonian system with $N$ degrees of freedom is subject to sufficiently rapid periodic driving, its energy evolves diffusively. We derive a Fokker-Planck equation that governs the evolution of the system's probability distribution in energy space, and we provide explicit expressions for the energy drift and diffusion rates. Our analysis suggests that the system generically relaxes to a long-lived prethermal state characterized by minimal energy absorption, eventually followed by more rapid heating. When $N\gg 1$, the system ultimately absorbs energy indefinitely from the drive, or at least until an infinite temperature state is reached.

Randomness can help one to implement quantum maps that cannot be realized in a deterministic fashion. Recently, it was discovered that explicitly treating a randomness source as a quantum system could double the efficiency as a catalyst for some tasks. In this work, we first show that every quantum channel that can be implemented with a randomness source without leaking information to it must be a catalysis. For that purpose, we prove a new no-go theorem that generalizes the no-hiding theorem, the no-secret theorem that states no quantum information can be shared with other systems as a secret without leaking some information. Second, we show that nondegenerate catalysts should be used classically when no extra dimension is allowed, which leads to the fact that the quantum advantage of a catalytic process strictly comes from the uniformness of the randomness source. Finally, we discuss a method to circumvent the previous result that achieves quantum advantage with nondegenerate catalyst uniformized by employing extra work space.

We investigate the second quantization form of the entanglement Hamiltonian (EH) of various subregions for the ground state of several interacting lattice fermions and spin models. The relation between the EH and the model Hamiltonian itself is an unsolved problem for the ground state of generic local Hamiltonians. In this paper, we demonstrate that the EH is practically local and its dominant components are related to the terms present in the model Hamiltonian up to a smooth spatially varying temperature even for (a) discrete lattice systems, (b) systems with no emergent conformal or Lorentz symmetry, and (c) subsystems with nonflat boundaries, up to relatively strong interactions. We show that the mentioned local temperature at a given point decays in a manner inversely proportional to its distance from the boundary between the subsystem and the environment. We find the subdominant terms in the EH as well and show that they are severely suppressed away from the boundaries of subsystem and are relatively small near them.

Ferromagnetism in two-dimensional ${\mathrm{CrI}}_3$ has generated a lot of excitement, and it was recently proposed that the spin-orbit coupling (SOC) in iodine may generate bond-dependent spin interactions leading to magnetic anisotropy. Here, we derive a microscopic spin model of $S=3/2$ on transition metals surrounded by heavy ligands in honeycomb Mott insulators using a strong-coupling perturbation theory. For ideal octahedra we find Heisenberg and Kitaev interactions, which favor the magnetic moment along the cubic axis via quantum fluctuations. When a slight trigonal distortion of the octahedra is present together with the SOC, three additional interactions arise, composed of the off-diagonal symmetric $\mathrm{\Gamma }$ and ${\mathrm{\Gamma }}^{\prime }$ and single-ion anisotropy. The resulting magnetic anisotropy pins the moment perpendicular to the honeycomb plane as observed in a single layer of ${\mathrm{CrI}}_3$, suggesting the significance of SOC and trigonal distortion in understanding magnetism of two-dimensional Mott insulators. A comparison with the spin-orbit coupled $J_{\mathrm{eff}}=1/2$ and $S=1$ models is also presented.

We theoretically investigate metasurface spatiotemporal dynamics by introducing laser chaotic dynamics into metasurface domain. The spatiotemporal dynamics takes advantage of both the time-dependent dynamics of optical chaos and the local spatial regulation capability of metasurface. Specifically, an optical spatiotemporal dynamic phenomenon, termed as vector-polarization optical chaos (VPOC), is demonstrated through asymmetric photonic spin-orbit interactions between all-dielectric metalens and chaotic polarization light from the vertical-cavity surface-emitting laser. The VPOC has spatially inhomogeneous polarization distribution with dynamically varied spatial structure and polarization singularity, while the corresponding intensity time series is temporally chaotic, characterized by positive largest Lyapunov exponent and finite correlation dimension. We found that the two nonlinear indices keep invariant for different polarization-resolved intensity time series due to the circular symmetry of metalens. Our results open an avenue for emerging spatiotemporal optical dynamics with metasurface and may find exciting applications in spatiotemporal light control, free-space secure optical communication, and optical chaos integrated chip.

The local constant field approximation (LCFA) is widely used in the study of QED effects in laser-matter interactions, with the justification that the classical strong-field parameter of the impinging laser beam is large. Here, the failure of this conjecture is demonstrated for an electron interacting with strong counterpropagating laser waves due to the emergence of an additional small time scale in the electron dynamics. Moreover, we identify a class of anomalous LCFA violation in which electrons turn sharply and leave the radiation formation zone much earlier than in the LCFA estimation. In contrast to previous observations of LCFA violation in a single laser beam, resulting in new low-harmonic peaks in the spectrum, here deviations from LCFA results are seen across the whole spectrum. A similar phenomenon is also demonstrated for an electron colliding with an ultrashort laser pulse. These results indicate the necessity of amending laser-plasma kinetic simulations in multiple beam laser configurations.

Generating ground states of any local Hamiltonians seems to be impossible in quantum polynomial time. In this paper, we give evidence for the impossibility by applying an argument used in the quantum-computational-supremacy approach. More precisely, we show that if ground states of any 3-local Hamiltonians can be approximately generated in quantum polynomial time with postselection, then $\mathsf{PP}=\mathsf{PSPACE}$. Our result is superior to the existing findings in the sense that we reduce the impossibility to an unlikely relation between classical complexity classes. We also discuss what makes efficiently generating the ground states hard for postselected quantum computation.

We study the phase-ordering dynamics of a uniform Bose gas in two dimensions following a quench into the ordered phase. We explore the crossover between dissipative and conservative evolution by performing numerical simulations within the classical field methodology. Regardless of the dissipation strength, we find clear evidence for universal scaling, with dynamical critical exponent $z$ characterizing the growth of the correlation length. In the dissipative limit we find growth consistent with the logarithmically corrected law ${[t/log(t/t_0)]}^{1/z}$, and exponent $z=2$, in agreement with previous studies. Decreasing the dissipation towards the conservative limit, we find strong numerical evidence for the expected growth law $t^{1/z}$. However, we observe a smooth crossover in $z$ that converges to an anomalous value distinctly lower than 2 at a small finite dissipation strength. We show that this lower exponent may be attributable to a power-law vortex mobility arising from vortex-sound interactions.

We observe a structural phase transition between two configurations of a superradiant crystal by coupling a Bose-Einstein condensate to an optical cavity and applying imbalanced transverse pump fields. The transition can be interpreted as a transition between two nonpolar, centro-symmetric structures involving a change in polarization. We find that this first order phase transition is accompanied by transient dynamics of the order parameter which we measure in real time. The phase transition and the excitation spectrum can be derived from a microscopic Hamiltonian, in quantitative agreement with our experimental data.

Stochastic resetting models diverse phenomena across numerous scientific disciplines. Current understanding stems from the renewal framework, which relates systems subject to global resetting to their nonresetting counterparts. Yet, in interacting many-body systems, even the simplest scenarios involving resetting give rise to the notion of local resetting, whose analysis falls outside the scope of the renewal approach. A prime example is that of diffusing particles with excluded volume interactions that independently attempt to reset their position to the origin of a one-dimensional lattice. With renewal rendered ineffective, we instead employ a mean-field approach whose validity is corroborated via extensive numerical simulations. The emerging picture sheds first light on the nontrivial interplay between interactions and resetting in many-body systems.

Whether long-range interactions allow for a form of causality in nonrelativistic quantum models remains an open question with far-reaching implications for the propagation of information and thermalization processes. Here, we study the out-of-equilibrium dynamics of the one-dimensional transverse Ising model with algebraic long-range exchange coupling. Using a state of the art tensor-network approach, complemented by analytic calculations and considering various observables, we show that a weak form of causality emerges, characterized by nonuniversal dynamical exponents. While the local spin and spin correlation causal edges are sub-ballistic, the causal region has a rich internal structure, which, depending on the observable, displays ballistic or superballistic features. In contrast, the causal region of entanglement entropy is featureless and its edge is always ballistic, irrespective of the interaction range. Our results shed light on the propagation of information in long-range interacting lattice models and pave the way to future experiments, which are discussed.