An intense terahertz pulse has the potential to control the polarization of ferroelectrics at the subpicosecond time scale. In some ferroelectrics, it has been reported that irradiation with a terahertz pulse on the order of 100 kV/cm modulates the polarization in a manner proportional to the electric field. If a stronger electric field is applied, it may be possible to alter the polarization nonlinearly or even cause it to disappear. However, such attempts have not been reported to date. In this paper, we aim to nonlinearly control ferroelectric polarization by irradiating an organic molecular compound tetrathiafulvalene-$p$-chloranil (TTF-CA), a typical electronic-type ferroelectric, with a terahertz pulse having an electric-field amplitude of up to 2.2 MV/cm. When the temperature is reduced, TTF-CA undergoes a neutral (N) to ionic (I) phase transition at $T_{\mathrm{c}}=81\mathrm{K}$, and the degree of charge transfer $\rho$ from CA to TTF changes from 0.3 to 0.6. In the I phase, it shows the ferroelectricity owing to the collective intermolecular charge transfer at $T_{\mathrm{c}}$. Therefore, if the I-to-N conversion is induced by a strong electric field, the ferroelectric polarization $P$ may change significantly. To investigate the changes in $\rho$ and $P$ along the electric-field waveform of the terahertz pulse in the ferroelectric I phase of TTF-CA, in this paper, a terahertz pump-optical reflectivity probe and second harmonic generation (SHG) probe measurements are performed. For the terahertz electric-field amplitudes $E_{\mathrm{THz}}<0.5\mathrm{MV}/\mathrm{cm}$, the changes in $\rho$ and $P$ are proportional to $E_{\mathrm{THz}}$. When $E_{\mathrm{THz}}>0.5\mathrm{MV}/\mathrm{cm}$ is applied parallel to $P$, the increases in $\rho$ and $P$ tend to become saturated. The increase in P is only ∼10% at a maximum electric-field amplitude of 2.2 MV/cm. In contrast, when $E_{\mathrm{THz}}$ is antiparallel to $P$, the decreases in $\rho$ and $P$ are proportional to $E_{\mathrm{THz}}$ up to 1.5 MV/cm. When $E_{\mathrm{THz}}$ is further increased to values >1.5 MV/cm, a partial I-to-N conversion occurs via quantum electron tunneling processes, and $P$ decreases in a nonlinear manner. The decrease in P reaches ∼30% at 2.2 MV/cm. These nonreciprocal changes in $\rho$ and $P$ are discussed while considering the valence instability characteristic of TTF-CA. Furthermore, several coherent oscillations are observed in the changes of reflectivity and SHG, which reflect the modulations of $\rho$ and $P$ due to molecular vibrations (lattice modes), respectively. A detailed analysis of the amplitudes and phases of these coherent oscillations reveals that a molecular vibration with a frequency of ∼90 $\mathrm{c}{\mathrm{m}}^{-1}$ is driven by changes in $\rho$ induced by a terahertz electric field and modulates $P$ significantly through the changes in the dimeric molecular displacements along the molecular stacking axis, that is, the polarization direction.

Itinerant ferromagnetism is one of the most-studied quantum phase transitions, the transition point and the nature of this phase transition being widely discussed. In dilute Fermi liquids, this analysis has been carried out up to second order in the gas parameter, where the results for any spin degeneracy are universal in terms of only the $s$-wave scattering length $a_0$. We extend this analysis to third order, where energies depend not only on $a_0$, but also on the $s$-wave effective range $r_0$ and the $p$-wave scattering length $a_1$. The introduction in the theory of these new parameters changes the transition point, with respect to the second-order estimation, and also can modify the nature of the phase transition itself. We analyze these interaction effects on the phase transition for different spin values. The emerging phase diagram shows that the type of ferromagnetic transition changes dramatically as a function of $r_0$ and $a_1$ and, importantly, that this classification is not solely determined by the spin value, as happens at second order.

We study a two-terminal Josephson junction with conventional superconductors and a normal region with a Rashba spin-orbit interaction, characterized by two Aharonov-Casher (AC) fluxes. When the superconducting phase difference equals $\pi$, the Andreev subgap spectrum may host zero-energy Weyl singularities associated with a vanishing normal-state reflection eigenvalue. With one of the AC fluxes playing the role of a quasimomentum, the junction can be viewed as an artificial one-dimensional chiral topological insulator. Its topological phase can be tuned by crossing a Weyl singularity by means of varying the remaining AC flux. By associating an additional component of the quasimomentum with the superconducting phase difference, an artificial Chern insulator is realized.

We employ real-space variational quantum Monte Carlo methods with resonating valence bond many-body wave functions to investigate electron correlation effects in the kagome system ${\text{Zn}}_x{\text{Cu}}_{4-x}{\text{O}}_6$. Using three trial wave functions of the Slater-Jastrow type, where (i) only the Jastrow correlation factor is optimized and the orbitals obtained by density functional theory, (ii) both the Jastrow factor and the Slater determinant are optimized, and (iii) additionally the Slater determinant is substituted by an antisymmetrized-geminal power-wave function, we analyze static and dynamic correlation energies across concentrations $x=0,\frac{1}{3},\frac{2}{3},1$. Optimizing the Slater determinant significantly enhances the correlation energy by approximately $\sim -73\left(4\right)\text{mHa}$ per electron. Eventually, the emergence of a quantum spin liquid state driven by a long-range correlation energy is discussed.

The Gross-Pitaevskii equation (GPE), a specialized form of the nonlinear Schrödinger equation (NLSE), plays a pivotal role in quantum mechanics, optics, and condensed matter physics, modeling phenomena such as superfluidity, quantum turbulence, and solitons, while serving as a cornerstone for advancing the study of nonlinear wave propagation and its technological applications. In this paper, we propose a solver, Complex-Valued Physics Informed Neural Network (CV-PINN) for NLSEs using physics-informed learning machines with complex representation. This method integrates complex values and algebraic properties directly into the neural network, with its structure mirroring the computation process of complex numbers, thereby significantly enhancing its ability to effectively solve complex problems. Additionally, we introduce a collocation-point sampling method called Predictive Dynamic Monitoring Sampling (PDM sampling), which adaptively adjusts the distribution of collocation points during training based on the model's historical performance. We conducted extensive empirical evaluations of the CV-PINN and the PDM sampling using a series of NLSE/GPEs (a total of 16 solved examples). Compared to the traditional real-valued PINN, the CV-PINN demonstrated higher accuracy, faster convergence, greater robustness, and better stability in these cases. Moreover, the PDM sampling proved to be effective in preventing model degradation and significantly enhancing the model's convergence speed and predictive accuracy when compared to traditional sampling methods. This advancement provides an approach and perspective for solving complex partial differential equations, thereby offering insights for the broader application of PINNs across various fields.

High-energy speckled lasers are known to exert ponderomotive forces on a plasma. This can reduce flow transverse to the propagation of the beams. When coupled with a supersonic flow, this has been shown to lead to the formation of a shock that travels against the flow. Experiments conducted on the OMEGA laser facility have used Thomson scattering to observe density and velocity changes consistent with this ponderomotively driven shock. Comparisons of the data with hydrodynamic simulations with the ponderomotive force, particle-in-cell simulations with a full Maxwell field solver, and hydrodynamic simulations without the ponderomotive force show that this shock feature is only reproduced when accounting for the ponderomotive force.

We investigate the optimal control of a continuous variable system, focusing on entanglement generation in an optomechanical system without utilizing Fock basis cutoffs. Using the Krotov algorithm to optimize the dynamics of the covariance matrix, we illustrate how to design a control objective function to manipulate the dynamics of the system to generate a desirable target state. We show that entanglement between the macroscopic mechanical mirror and the quantum optical cavity can be reliably generated through imposing the control on the detuning of the external laser field. It has been shown that the control may still be achieved when imposing spectral constraints on the external field to restrict it to low-frequency components. In addition, we systematically study the effects of quantum control on non-Markovian open system dynamics. We observe that memory effects can play a beneficial role in mitigating detrimental impacts of environmental noises. Specifically, the generated entanglement shows a reduced decay rate in the presence of these memory effects.

The fragile-to-strong glass transition is a fascinating phenomenon that still presents many theoretical and experimental challenges. A major one is how to tune the fragility of a glass-forming liquid. Here, we study a two-dimensional (2D) system composed of vortices in a superconducting film, which effectively behaves as a 2D glass-forming liquid. We show that the kinetic fragility in this system can be experimentally varied by tuning a single parameter: the external magnetic field $H$ applied perpendicularly to the film. This conclusion is supported by the direct comparison between the analysis of experimental measurements in an amorphous MoGe superconducting film and Monte Carlo simulations in a disordered $XY$ model, that captures the universality class of the two-step melting transition. We show that by increasing disorder strength, a fragile-to-strong transition is induced, in close similarity with the experimental findings in a magnetic field. Our numerical results shed light on the evolution of the dynamical heterogeneity from a fragile-to-strong glass, as due to the subtle interplay between caging effects arising from hexatic order and strong random pinning.

Dissipation always exists in real environments, and it can cause decoherence during transfer of quantum states. To avoid decoherence, dissipation is usually shielded. However, dissipation is difficult to avoid in real cases. Thus, how to achieve efficient quantum state transfer in dissipation environments, although it will receive great attention, remains a challenge. Here we demonstrate that dissipation can be utilized to realize robust control of quantum state transfer instead of being avoided. Our scheme is realized by constructing Liouvillian exceptional point (LEP). By tuning dissipation, the exchange of eigenvectors and nonadiabatic transition near the LEP can be modulated, thereby controlling transfer and chirality of topological quantum state. Furthermore, we have experimentally validated such a scheme on a quantum walk platform. Our work opens up a different avenue for quantum information process in real systems.

Einstein's general theory of relativity not only revolutionized our understanding of the universe but also led to numerous gravitational applications on large spatial scales, such as gravitational-wave astronomy and the operation of the global positioning system. On Earth, the gravitational redshift has been experimentally observed over spatial scales ranging from a few millimeters to thousands of kilometers. However, finding an application of gravitational effects in a quantum system at small spatial extensions on Earth remains a challenge. Along this line, we introduce a structured x-ray waveguide that serves as an x-ray mode converter, and its performance is influenced by an altitude change in the order of millimeters or even microns. Our results suggest that the gravitational redshift can be another way to fine adjust the x-ray detuning for any devices using a nuclear clock transition.

How do cells tune emergent properties at the scale of tissues? One class of such emergent behaviors are rigidity transitions, in which a tissue changes from a solidlike to a fluidlike state or vice versa. Here we introduce a way for a tissue described by a vertex model to tune its rigidity by using “tunable degrees of freedom.” We use the vertex model elastic energy as a cost function and the cell stiffnesses, target shapes, and target areas as different sets of degrees of freedom describing cell-cell interactions that can be tuned to minimize the cost function. We show that the rigidity transition is unaffected when cell stiffnesses are treated as tunable degrees of freedom. When preferred shapes or areas are treated as tunable degrees of freedom, however, induced spatial correlations in target cell shapes or areas shift the rigidity transition. These observations suggest that tissues can coordinate changes in cell-scale properties, treated here as tunable degrees of freedom, to achieve desired tissue-scale behaviors.

Excitons, namely, neutral excitations in a system of electrons arising from the electron-hole interaction, are often essential to explain optical measurements in materials. They are governed by the Bethe-Salpeter equation, which can be cast into a matrix form that is formally analogous to the one for electrons at the mean-field level. However, constructing the corresponding excitonic Hamiltonian in practice is challenging, specially from a computational perspective if one wishes to surpass effective models. Methods that enable such calculations from the different density-functional theory frameworks currently available are, therefore, convenient. In this work, we present an approach to solve the BSE starting from a self-consistent calculation in any nonmetallic solid by evaluating the electron-hole kernel in real space with a localized, Gaussian-type basis. It is based on the Gaussian density fitting or resolution of the identity approximation to reduce the initial quartic scaling in the basis dimension, in combination with the use of Ewald-type potential functions to automatically sum the conditionally convergent lattice series. The method inherits the features of the localized basis, in particular the reduced computational requirements due to the small and tunable Hilbert-space dimension, the natural adaptation to lower-dimensional systems or the possibility to evaluate optical matrix elements exactly. As an illustration of the computational implementation, we provide examples of exciton spectra and optical absorption in some paradigmatic 2D and 3D materials where the single-particle approximation fails qualitatively.

We numerically examine the depinning, sliding, and melting of commensurate and incommensurate Wigner crystals on two-dimensional hexagonal periodic substrates near fillings of $1/3,1/2$, and $2/3$ to model the dynamics of generalized Wigner crystals in moiré heterostructures. At low temperatures where thermal fluctuations are irrelevant, for commensurate fillings we find a strongly pinned state that depins into a sliding crystal, while at incommensurate fillings the depinning threshold is strongly reduced. For fillings below $1/2$, the depinning occurs in a two-step process. Above the first depinning threshold, there is an extended range of drives where the conduction occurs via the sliding of antikinks along the charge stripes, followed by a second threshold where all the charges begin to slide. At finite temperatures, the external driving reduces the effective melting temperature at commensurate fillings and enhances creep at incommensurate fillings. We show that depinning into different sliding states, such as moving fluids or moving crystals, produces nonlinear features in the transport curves. We also show that transport is asymmetric on either side of a commensurate filling due to the different dynamics for interstitials versus holes in the commensurate structure. A variety of sliding states should be accessible for generalized Wigner crystals at finite temperatures even for low drives. If experiments can realize sliding dynamics in moiré systems, it would open another class of commensurate and incommensurate phases for study. Additionally, the sliding dynamics and antikink flow could provide unique functionalities for charge transport in moiré heterostructures.

We propose a linear-optical scheme that allows encoding grid-state quantum bits (qubits) into a bosonic mode using cat state and postselection as sources of non-Gaussianity in the encoding. As a linear-optical realization of the quantum-walk encoding scheme in [Lin et al., Quantum Inf. Process. 19, 272 (2020)], we employ the cat state as a quantum coin that enables encoding approximate Gottesman-Kitaev-Preskill qubits through quantum walk of a squeezed vacuum state in phase space. We show that the conditional phase-space displacement necessary for the encoding can be realized through a Mach-Zehnder interferometer (MZI) assisted with ancillary cat-state input under appropriate parameter regimes. By analyzing the fidelity of the MZI-based displacement operation, we identify the region of parameter space over which the proposed linear-optical scheme can generate grid-state qubits with high fidelity. With adequate parameter setting, our proposal should be accessible to current optical and superconducting-circuit platforms in preparing grid-state qubits for bosonic modes in the, respectively, optical and microwave domains.

We numerically investigate normal diffusion in a two-dimensional athermal suspension of active particles undergoing motility-induced phase separation. The particles are modeled as achiral Janus disks with fixed self-propulsion speed and weakly fluctuating orientation. When plotted versus the overall suspension packing fraction, the relevant diffusion constant traces a hysteresis loop with sharp jumps in correspondence with the binodal and spinodal of the gaseous phase. No hysteresis loop is observed between the spinodal and binodal of the dense phase, as they appear to overlap. Moreover, even under steady-state phase separation, the particle displacement distributions exhibit non-Gaussian normal diffusion with transient fat (thin) tails in the presence (absence) of phase separation.

In Earth's aquatic environments and the human body, microbial swimmers often accumulate at interfaces within layered systems, forming colonies known as active carpets. These bioactive layers enhance mass transport and diffusion in fluid media. Here we study the hydrodynamic behavior induced by active carpets within confined semi-infinite fluid layers, such as the one found in the sea surface microlayer. By deriving analytical expressions and performing numerical simulations, we explore how geometrical and viscous confinement (layer thickness and viscosity ratio) influence hydrodynamic fluctuations and passive tracer dynamics. Our findings reveal anisotropic distributions of fluctuations, characterized by three distinct regions: near the active carpet and fluid-fluid interface (Region I), vertical fluctuations dominate; in an intermediate region (Region II), fluctuations become isotropic; and near the free surface (Region III), horizontal fluctuations prevail. The results also demonstrate the emergence of coherent vortical structures in highly confined systems, with roll-like patterns governed by the thickness of the confined layer and the sharpness in viscosity transitions. The insights provided by this work have implications for understanding biogenic flow patterns and transport processes in natural and engineered environments, offering potential applications in areas such as microbial ecology, biofilm management, and microfluidic technologies.