In the dynamics of open quantum systems, the backflow of information to the reduced system under study has been suggested as the actual physical mechanism inducing memory and thus leading to non-Markovian quantum dynamics. To this aim, the trace-distance revivals between distinct evolved system states have been shown to be subordinated to the establishment of system-environment correlations or changes in the environmental state. We show that this interpretation can be substantiated also for a class of entropic quantifiers. We exploit a suitably regularized version of Umegaki’s quantum relative entropy, known as telescopic relative entropy, that is tightly connected to the quantum Jensen-Shannon divergence. In particular, we derive general upper bounds on the telescopic relative entropy revivals conditioned and determined by the formation of correlations and changes in the environment. We illustrate our findings by means of examples, considering in particular the Jaynes-Cummings model and a phase covariant dynamics.

Scalar fields coupled to the Gauss-Bonnet invariant can undergo a tachyonic instability, leading to spontaneous scalarization of black holes. Studies of this effect have so far been restricted to single black hole spacetimes. We present the first results on dynamical scalarization in head-on collisions and quasicircular inspirals of black hole binaries with numerical relativity simulations. We show that black hole binaries can either form a scalarized remnant or dynamically descalarize by shedding off its initial scalar hair. The observational implications of these findings are discussed.

The quantum system under periodical modulation is the simplest path to understand the quantum nonequilibrium system because it can be well described by the effective static Floquet Hamiltonian. Under the stroboscopic measurement, the initial phase is usually irrelevant. However, if two uncorrelated parameters are modulated, their relative phase cannot be gauged out so that the physics can be dramatically changed. Here, we simultaneously modulate the frequency of the lattice laser and the Rabi frequency in an optical lattice clock (OLC) system. Thanks to the ultrahigh precision and ultrastability of the OLC, the relative phase could be fine-tuned. As a smoking gun, we observed the interference between two Floquet channels. Finally, by experimentally detecting the eigenenergies, we demonstrate the relation between the effective Floquet Hamiltonian and the one-dimensional topological insulator with a high winding number. Our experiment not only provides a direction for detecting the phase effect but also paves a way in simulating the quantum topological phase in the OLC platform.

Runaway electron populations seeded from the hot tail generated by the rapid cooling in plasma-terminating disruptions are a serious concern for next-step tokamak devices such as ITER. Here, we present a comprehensive treatment of the thermal quench, including the superthermal electron dynamics, heat and particle transport, atomic physics, and radial losses due to magnetic perturbations: processes that are strongly linked and essential for the evaluation of the runaway seed in disruptions mitigated by material injection. We identify limits on the injected impurity density and magnetic perturbation level for which the runaway seed current is acceptable without excessive thermal energy being lost to the wall via particle impact. The consistent modeling of generation and losses shows that runaway beams tend to form near the edge of the plasma, where they could be deconfined via external perturbations.

The charge states of ions in dense plasmas fluctuate due to collisional ionization and recombination. Here, we show how, by modifying the ion interaction potential, these fluctuations can mediate energy exchange between the plasma electrons and ions. Moreover, we develop a theory for this novel electron-ion energy transfer mechanism. Calculations using a random walk approach for the fluctuations suggest that the energy exchange rate from charge state fluctuations could be comparable to direct electron-ion collisions. This mechanism is, however, predicted to exhibit a complex dependence on the temperature and ionization state of the plasma, which could contribute to our understanding of significant variation in experimental measurements of equilibration times.

We study an oblique spacetime crystal realized by a monoatomic crystal in which a sound wave propagates, and analyze its quasienergy band structure starting from a tight-binding Bloch band for the static crystal. We investigate Floquet-Bloch oscillations under an external field, which show different characteristics for different band topologies. We also discover intraband Zener tunneling beyond the adiabatic limit, which effectively converts between different band topologies. Our results indicate the possibility of energy conversion between the sound wave and a dc electric field.

THz magnetization dynamics of antiferromagnetically coupled spins in ferrimagnetic ${\mathrm{Tm}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}$ is excited by a picosecond single-cycle pulse of a magnetic field and probed with the help of the magneto-optical Faraday effect. Data analysis combined with numerical modeling shows that the dynamics corresponds to the exchange mode excited by the Zeeman interaction of the THz magnetic field with the spins. We argue that THz-pump–IR-probe experiments on ferrimagnets offer a unique tool for quantitative studies of dynamics and mechanisms to control antiferromagnetically coupled spins.

Through an extensive series of high-precision numerical computations of the optimal complete photonic band gap (PBG) as a function of dielectric contrast $\alpha$ for a variety of crystal and disordered heterostructures, we reveal striking universal behaviors of the gap sensitivity $\mathcal{S}(\alpha )\equiv d\mathrm{\Delta }(\alpha )/d\alpha$, the first derivative of the optimal gap-to-midgap ratio $\mathrm{\Delta }(\alpha )$. In particular, for all our crystal networks, $\mathcal{S}(\alpha )$ takes a universal form that is well approximated by the analytic formula for a 1D quarter-wave stack, ${\mathcal{S}}_{\mathrm{QWS}}(\alpha )$. Even more surprisingly, the values of $\mathcal{S}(\alpha )$ for our disordered networks converge to ${\mathcal{S}}_{\mathrm{QWS}}(\alpha )$ for sufficiently large $\alpha$. A deeper understanding of the simplicity of this universal behavior may provide fundamental insights about PBG formation and guidance in the design of novel photonic heterostructures.

We report on a signal-to-noise ratio characterizing the generation of identical photon pairs of more than 4 orders of magnitude in a ring resonator system. Parasitic noise, associated with single-pump spontaneous four-wave mixing, is essentially eliminated by employing a novel system design involving two resonators that are linearly uncoupled but nonlinearly coupled. This opens the way to a new class of integrated devices exploiting the unique properties of identical photon pairs in the same optical mode.

We demonstrate that the interplay between a nonlinearity and $\mathcal{PT}$ symmetry in a periodic potential results in peculiar features of nonlinear periodic solutions. These include thresholdless symmetry breaking and asymmetric (multi-)loop structures of the nonlinear Bloch spectrum, persistence of unbroken $\mathcal{PT}$ symmetry even after the gap is closed, nonmonotonic dependence of the $\mathcal{PT}$ phase transition on the defocusing nonlinearity, and enhanced stability of the nonlinear states corresponding to the loop structures. The asymmetry and the loop structure of the spectrum are explained within the framework of a two-mode approximation and an effective potential theory and are validated numerically.

Relativistic magnetized shocks are a natural source of coherent emission, offering a plausible radiative mechanism for fast radio bursts (FRBs). We present first-principles 3D simulations that provide essential information for the FRB models based on shocks: the emission efficiency, spectrum, and polarization. The simulated shock propagates in an $e^{\pm }$ plasma with magnetization $\sigma >1$. The measured fraction of shock energy converted to coherent radiation is $\simeq {10}^{-3}{\sigma }^{-1}$, and the energy-carrying wave number of the wave spectrum is $\simeq 4{\omega }_c/c$, where ${\omega }_c$ is the upstream gyrofrequency. The ratio of the $O$-mode and $X$-mode energy fluxes emitted by the shock is $\simeq 0.4{\sigma }^{-1}$. The dominance of the $X$ mode at $\sigma \gg 1$ is particularly strong, approaching 100% in the spectral band around $2{\omega }_c$. We also provide a detailed description of the emission mechanism for both $X$ and $O$ modes.

The lack of methods to experimentally detect and quantify entanglement in quantum matter impedes our ability to identify materials hosting highly entangled phases, such as quantum spin liquids. We thus investigate the feasibility of using inelastic neutron scattering (INS) to implement a model-independent measurement protocol for entanglement based on three entanglement witnesses: one-tangle, two-tangle, and quantum Fisher information (QFI). We perform high-resolution INS measurements on ${\mathrm{Cs}}_2{\mathrm{CoCl}}_4$, a close realization of the $S=1/2$ transverse-field $XXZ$ spin chain, where we can control entanglement using the magnetic field, and compare with density-matrix renormalization group calculations for validation. The three witnesses allow us to infer entanglement properties and make deductions about the quantum state in the material. We find QFI to be a particularly robust experimental probe of entanglement, whereas the one and two-tangles require more careful analysis. Our results lay the foundation for a general entanglement detection protocol for quantum spin systems.

An optical frequency comb consists of a set of discrete and equally spaced frequencies and has found wide applications in the synthesis over a broad range of spectral frequencies of electromagnetic waves and precise optical frequency metrology. Despite the analogies between magnons and photons in many aspects, the analog of an optical frequency comb in magnonic systems has not been reported. Here, we theoretically study the magnon-skyrmion interaction and find that a magnonic frequency comb (MFC) can be generated above a threshold driving amplitude, where the nonlinear scattering process involving three magnons prevails. The mode spacing of the MFC is equal to the breathing-mode frequency of the skyrmion and is thus tunable by either electric or magnetic means. The theoretical prediction is verified by micromagnetic simulations, and the essential physics can be generalized to a large class of magnetic solitons. Our findings open a new pathway to observe frequency comb structures in magnonic devices that may inspire the study of fundamental nonlinear physics in spintronic platforms in the future.

Lorentzian distributions have been largely employed in statistical mechanics to obtain exact results for heterogeneous systems. Analytic continuation of these results is impossible even for slightly deformed Lorentzian distributions due to the divergence of all the moments (cumulants). We have solved this problem by introducing a “pseudocumulants” expansion. This allows us to develop a reduction methodology for heterogeneous spiking neural networks subject to extrinsic and endogenous fluctuations, thus obtaining a unified mean-field formulation encompassing quenched and dynamical sources of disorder.

We experimentally study two-dimensional (2D) Coulomb crystals in the “radial-2D” phase of a linear Paul trap. This phase is identified by a 2D ion lattice aligned entirely with the radial plane and is created by imposing a large ratio of axial to radial trapping potentials. Using arrays of up to 19 ${}^{171}{\mathrm{Yb}}^{+}$ ions, we demonstrate that the structural phase boundaries of such crystals are well described by the pseudopotential approximation, despite the time-dependent ion positions driven by intrinsic micromotion. We further observe that micromotion-induced heating of the radial-2D crystal is confined to the radial plane. Finally, we verify that the transverse motional modes, which are used in most ion-trap quantum simulation schemes, are well-predictable numerically and remain decoupled and cold in this geometry. Our results establish radial-2D ion crystals as a robust experimental platform for realizing a variety of theoretical proposals in quantum simulation and computation.

Digital quantum simulators provide a diversified tool for solving the evolution of quantum systems with complicated Hamiltonians and hold great potential for a wide range of applications. Although much attention is paid to the unitary evolution of closed quantum systems, dissipation and noise are vital in understanding the dynamics of practical quantum systems. In this work, we experimentally demonstrate a digital simulation of an open quantum system in a controllable Markovian environment with the assistance of a single ancillary qubit. By Trotterizing the quantum Liouvillians, the continuous evolution of an open quantum system is effectively realized, and its application in error mitigation is demonstrated by adjusting the simulated noise intensities. High-order Trotter for open quantum dynamics is also experimentally investigated and shows higher accuracy. Our results represent a significant step toward hardware-efficient simulation of open quantum systems and error mitigation in quantum algorithms in noisy intermediate-scale quantum systems.