Rayleigh-Bloch waves are guided acoustic waves propagating along a periodic line of inclusions placed inside an open, infinite medium. Below the sound cone, they are transversely evanescent on both sides of the line of inclusions. Guidance is then achieved without any cladding surrounding the segmented core. Inclusions usually impose definite boundary conditions, resulting in a single guided band. We consider instead the case of permeable, slow inclusions inside a fast medium. Introducing the concept of guided quasinormal modes, we obtain the complex dispersion relation taking into account radiation at infinity. We thus show that multiple bands of leaky Rayleigh-Bloch waves appear and that guided bound states in the continuum arise as a result of the combination of symmetry and periodicity.

The quantum Mpemba effect (QME) describes the counterintuitive phenomenon in which a system farther from equilibrium reaches the steady state faster than one closer to equilibrium. However, ambiguity in defining a suitable distance measure between quantum states has led to varied interpretations across different contexts. Here we propose the intrinsic quantum Mpemba effect (IQME), defined using the trajectory length traced by the quantum state as a more appropriate measure of distance—distinct from previous trajectory-independent metrics. By treating quantum states as points in a Riemannian space defined by statistical distance, the trajectory length emerges as a more natural and accurate characterization of the counterintuitive dynamics, drawing an analogy to the classical Brachistochrone problem. We demonstrate the existence of IQME in Markovian systems and extend its definition to quantum circuits, thereby establishing a unified framework applicable to both open and closed systems. Notably, we observe an IQME in a U(1)-symmetric circuit, offering insights into the rates of quantum thermalization for different initial states. This work reveals a relatively unexplored nonequilibrium quantum phenomenon, thereby advancing our understanding of quantum state evolution.

Vacancy defects in disordered magnetic materials are known to act as effective spins, “quasispins,” in response to an external magnetic field. In the dilute limit, the contributions of such quasispins to the magnetic susceptibility ${\chi }_{\text{vac}}\left(T\right)\propto N_{\text{vac}}/T$ are singular in the limit of low temperatures $T$ and match those of free spins. With increasing the density of vacancies, their interactions may become essential. Motivated by frustrated and quasi-one-dimensional magnetic materials, we show by exact computation that the correlation of the quasispins of different vacancies matches the spin-spin correlators in the vacancy-free materials for Ising chains with nearest-neighbor and next-to-nearest-neighbor interactions. We also compute the first virial correction to the susceptibility of a magnetic material due to the interactions of vacancy quasispins. We then provide a phenomenological generalization of our results to a generic system that has short-range antiferromagnetic order and lacks long-range order. We predict that if the vacancy defect does not disrupt the short-range antiferromagnetic order around it, the quasispin value matches the value of spins of the magnetic atoms in the material, and the correlators of the quasispins of different vacancies match the spin-spin correlators in the vacancy-free material.

We present a systematic analysis of cavity effects on the decay dynamics of an open magnonic system. The Purcell effect on the magnon oscillator decay is thoroughly examined for both driven and nondriven scenarios with realistic parameters and initial conditions. Analytical conditions are determined to distinguish between strong and weak coupling regimes, corresponding to oscillatory and pure decay behaviors, respectively. Additionally, our theory predicts the decay of the photon mode within the cavity-magnonic open system, demonstrating excellent agreement with existing experimental data. Our findings and methodologies provide valuable insights for advancing research in cavity magnonic quantum control, quantum information processing, and the development of magnonic quantum devices.

The origin of Néel-type magnetic skyrmion formation in the two-dimensional magnetic material ${\mathrm{Fe}}_3{\mathrm{GeTe}}_2$ is of significant theoretical interest due to its potential applications in spintronic devices. In this study, we investigate the magnetic exchange interactions in ${\mathrm{Fe}}_3{\mathrm{GeTe}}_2$ monolayers using density functional theory and Monte Carlo simulations. Our findings highlight the critical role of spin-orbit coupling (SOC) in the formation of noncollinear magnetic textures in ${\mathrm{Fe}}_3{\mathrm{GeTe}}_2$. We demonstrate that the energy differences induced by SOC vary with the spin-spiral vector, and that SOC significantly influences higher-order exchange interactions, which further affect the stability and formation of magnetic textures, including skyrmions.

Cross-nonlinear responses to an electric current and a temperature gradient have been investigated in a superconducting MoGe film attached to a ferrimagnetic insulator ${\mathrm{Y}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}$. We found that the MoGe film generates an electric voltage proportional to both the applied electric current and temperature gradient in the superconducting vortex-liquid phase of the MoGe. The observed cross-nonlinear voltage can be attributed to the motion of vortex strings that sense the difference in magnetic environment between the top and bottom surfaces of the MoGe film on the ${\mathrm{Y}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}$. The effect demonstrated here expands the scope of thermoelectric physics in low-symmetry materials.

The performance of quantum error correcting (QEC) codes is often studied under the assumption of spatiotemporally uniform error rates. On the other hand, experimental implementations almost always produce heterogeneous error rates, in either space or time, as a result of effects such as imperfect fabrication and/or cosmic rays. It is therefore important to understand if and how their presence can affect the performance of QEC in qualitative ways. In this work, we study the effects of nonuniform error rates in the representative examples of the 1D repetition code and the 2D toric code, focusing on when they have extended spatiotemporal correlations; these may arise, for instance, from rare events (such as cosmic rays) that temporarily elevate error rates over the entire code patch. These effects can be described in the corresponding statistical mechanics models for decoding, where long-range correlations in the error rates lead to extended rare regions of weaker coupling. For the 1D repetition code where the rare regions are linear, we find two distinct decodable phases: a conventional ordered phase in which logical failure rates decay exponentially with the code distance, and a rare-region dominated Griffiths phase in which failure rates are parametrically larger and decay as a stretched exponential. In particular, the latter phase is present when the error rates in the rare regions are above the bulk threshold. For the 2D toric code where the rare regions are planar, we find no decodable Griffiths phase: rare events which boost error rates above the bulk threshold lead to an asymptotic loss of threshold and failure to decode. Unpacking the failure mechanism implies that techniques for suppressing extended sequences of repeated rare events (which, without intervention, will be statistically present with high probability) will be crucial for QEC with the toric code.

We present a method for simulating the dynamics of an open electronic system on a quantum computer. This approach entails midcircuit measurements and resets to simulate the addition or removal of electrons from the system. Our method provides a way to apply nonreversible operations to a quantum computer without the need for additional qubits. Using this method, we simulate the dynamics of an open electronic system consisting of a chain of electrons positioned between two conductive leads on the $ibm\_torino$ quantum computer. We expect the method to be generally applicable to open systems.

Recent experiments have measured flux-dependent capacitance at radio frequencies, leading to the potential for a fast parity read-out of a Majorana qubit. In this work, we argue that the quantum dot used in the capacitance measurement can be reasonably approximated by a noninteracting weakly coupled orbital. We then predict the measured flux and parity-dependent capacitance for several parameter regimes of the disordered Majorana nanowire model that are both topological and trivial. Following this, we study how such a fast capacitance readout can be used to characterize the quantum coherence of a Majorana nanowire-based qubit using Rabi oscillations. We additionally show that such measurements, if made possible by coherent interwire tunneling, would provide a valuable way of characterizing the low energy states in the frequency domain.

Ultrafast irradiation of correlated electronic systems triggers complex dynamics involving quasiparticle excitations, doublons, charge carriers, and spin fluctuations. To describe these effects, we develop an efficient nonequilibrium approach, dubbed $D\text{−}GW$, that enables a self-consistent treatment of local correlations within dynamical mean-field theory (DMFT) and spatial charge and spin fluctuations that are accounted for simultaneously within a diagrammatic framework. The method is formulated in the real-time domain and provides direct access to single- and two-particle momentum- and energy-dependent response functions without the need for analytical continuation, which is required in Matsubara frequency-based approaches. We apply the $D\text{−}GW$ method to investigate the dynamics of a photoexcited extended Hubbard model, the minimal system that simultaneously hosts strong charge and spin fluctuations. Focusing on the challenging parameter regime near the Mott transition, we demonstrate that correlated metals and narrow-gap Mott insulators undergo distinct thermalization processes involving complex energy transfer between single-particle and collective electronic excitations.

Flat-band systems have attracted tremendous attention due to their important role in exotic strongly correlated phenomena, such as superconductivity, magnetism, and fractional Chern insulators recently observed in moiré materials. Here we systematically demonstrate the emergence of degenerate flat bands in different lattice models with simple near-neighbor hopping parameters, including the kagomé lattice, the kagomé-honeycomb lattice and the star lattice. Interestingly, the degeneracy can be lifted by staggered magnetic fluxes, typically leading to a couple of nearly flat topological bands with high Chern numbers $C=\pm 1,\pm 3,\pm 4$. Finally we show the possibility of fractional Chern insulators when interacting electrons partially fill these nearly flat Chern bands.

We present a scalable machine learning (ML) framework for large-scale kinetic Monte Carlo (kMC) simulations of itinerant electron Ising systems. As the effective interactions between Ising spins in such itinerant magnets are mediated by conducting electrons, the calculation of energy change due to a local spin update requires solving an electronic structure problem. Such repeated electronic structure calculations could be overwhelmingly prohibitive for large systems. Assuming the locality principle, a convolutional neural network (CNN) model is developed to directly predict the effective local field and the corresponding energy change associated with a given spin update based on Ising configuration in a finite neighborhood. As the kernel size of the CNN is fixed at a constant, the model can be directly scalable to kMC simulations of large lattices. Our approach is reminiscent of the ML force field models widely used in first-principles molecular dynamics simulations. Applying our ML framework to a square-lattice double-exchange Ising model, we uncover unusual coarsening of ferromagnetic domains at low temperatures. Our work highlights the potential of ML methods for large-scale modeling of similar itinerant systems with discrete dynamical variables.

Electron-phonon ($e$-ph) interactions arise in many strongly correlated quantum materials from the modulation of the nearest-neighbor hopping integrals, as in the celebrated Su-Schrieffer-Heeger (SSH) model. Nevertheless, relatively few nonperturbative studies of correlated SSH models have been conducted in dimensions greater than one, and those that have been done have primarily focused on bond models, where generalized displacements independently modulate each hopping integral. We conducted a sign-problem free determinant quantum Monte Carlo study of the optical SSH-Hubbard model on a two-dimensional square lattice, where site-centered phonon modes simultaneously modulate pairs of nearest-neighbor hopping integrals. We report the model's low-temperature phase diagram in the challenging adiabatic regime ($\mathrm{\Omega }/E_{\mathrm{F}}\sim 1/8$). It exhibits insulating antiferromagnetic Mott and bond-order-wave (BOW) phases with a narrow region of coexistence between them. We also find that a critical $e$-ph coupling is required to stabilize the BOW phase in the small $U$ limit. Lastly, in stark contrast to recent findings for the model's bond variant, we find no evidence for a long-range antiferromagnetism in the pure $(U/t=0)$ optical SSH model.

We investigate the electronic properties of two-dimensional electron gases (2DEGs) subjected to a periodic patterned gate. By incorporating the superlattice (SL) potential induced by patterning into the Schrödinger equation, we develop a methodology for obtaining exact analytical solutions. These solutions enable us to construct a comprehensive phase diagram illustrating the emergence of narrow bands and pseudo-Landau levels driven by the SL potential. To complement the analytical approach, we employ a standard plane-wave formalism to track the evolution of the band structure as the SL strength increases. By breaking the inversion symmetry of the SL potential, we find a nontrivial Berry curvature. Furthermore, we introduce a self-consistent Hartree screening to account for the interplay between the SL potential and electronic interactions. Our findings not only reveal the emergence of a nontrivial quantum geometry and a competition between SL strength and electron-electron interactions but also highlight the value of exact analytical solutions for understanding and engineering electronic phases in patterned 2DEG systems.

The local molecular motion of $cis$-polybutadiene, a typical polymeric material exhibiting a glass transition ($T_{\mathrm{g}}=168\mathrm{K}$), is investigated by the spin relaxation of muonated radicals, where the relaxation is induced by the fluctuation of hyperfine (HF) fields exerted from an unpaired electron to a nearby muon and surrounding protons. The relaxation rate $1/T_{\mu }$ measured under various longitudinal magnetic fields is analyzed using the recently developed theory of spin relaxation to consider the coexistence of quasistatic and fluctuating HF fields, where the fluctuation frequency for the latter $\nu$ is evaluated over a temperature $T$ range of 5–320 K. The obtained $\nu \left(T\right)$ is found to be well reproduced by the Arrhenius relation, and the activation energy and preexponential factor are in good agreement with those for the “elemental process” revealed by quasielastic neutron scattering and attributed to a fluctuation across three carbon-carbon bonds. This result demonstrates that muonated-radical spin relaxation is a promising approach for direct access to local molecular motions in the subnanosecond range and for their detailed modeling at the atomic scale.

We consider a coupling element based on a symmetric superconducting quantum interference device (SQUID) and show that it mediates a two-photon interaction. This and other inductive interactions due to the SQUID can be switched off in situ. We derive the system Hamiltonian for a coupled resonator and rf SQUID. The rf SQUID dwells in the vicinity of its metastable well holding a number of energy states and acts as an artificial atom. We discuss how the Josephson symmetry breaks owing to magnetic fields in the superconducting loops—both directly and via a nonzero superconducting phase difference over the rf SQUID. We assess that the two-photon coupling strength reaches 18 MHz which can exceed the single-photon capacitive interaction in the coupler.