Superconducting tunnel junctions constitute the units of superconducting quantum circuits and are massively used both for quantum sensing and quantum computation. In previous works, we predicted the existence of a nonlinear thermoelectric effect in a electron-hole symmetric system, namely, a thermally biased tunnel junction between two different superconductors, where the Josephson effect is suppressed. In this paper, we investigate the impact of the phase-coherent contributions on the thermoelectric effect by tuning the size of the Josephson coupling changing the flux of a direct-current superconducting quantum interference device (dc-SQUID). For a suppressed Josephson coupling, the system generates a finite average thermoelectric signal, combined with an oscillation due to the standard ac Josephson phenomenology. At large Josephson couplings, the thermoelectricity induces an oscillatory behavior with zero average value of the current and voltage, with an amplitude and a frequency associated to the Josephson coupling strength, and ultimately tuned by the dc-SQUID magnetic flux. In conclusion, we demonstrate the ability to control the dynamics of the spontaneous breaking of the electron-hole symmetry. Furthermore, we compute how the flux applied to the dc-SQUID and the lumped elements of the circuit determine the frequency of the thermoelectric signal across the structure, and we envision a frequency modulation application.

Recent interest in topological nature in condensed matter physics has revealed the essential role of Berry curvature in the anomalous Hall effect (AHE). However, since a large Hall response originating from Berry curvature has been reported in quite limited materials, the detailed mechanism remains unclear at present. Here, we report the discovery of a large AHE triggered by a pressure-induced magnetic phase transition in elemental $\alpha$-Mn. The AHE is absent in the noncollinear antiferromagnetic phase at ambient pressure, whereas a large AHE is observed in the weak ferromagnetic phase under high pressure despite the small magnetization of $\approx 0.02{\mu }_B$/Mn. Our results indicate that the emergence of the AHE in $\alpha$-Mn is governed by the symmetry of the underlying magnetic structure, providing a direct evidence of a switch between a zero and nonzero contribution of the Berry curvature across the phase boundary. $\alpha$-Mn can be an elemental and tunable platform to reveal the role of Berry curvature in AHE.

A high-energy electron beam coupled to an optical field experiences a quantized energy modulation by multiples of the photon energy, originating from the temporal periodicity of the optical field by virtue of intercycle interference. Here we investigate the quantum interference occurring at shorter timescales, namely, within half an optical cycle, which is called intracycle interference. We show that the sub-half-cycle energy and phase modulation are imprinted into and largely modulate electron energy spectra regardless of the laser pulse duration. The intracycle effect is universal, meaning that it shows up for almost any electron velocity and optical wavelength. It thus facilitates coherent control of free-electron beams in microscopes or accelerators with a resolution of below an optical cycle, i.e., on attosecond timescales. The results obtained also apply to multiphoton and attosecond physics in atoms, molecules, and solids.

We consider an overdamped Brownian particle subject to an asymptotically flat potential with a trap of depth $U_0$ around the origin. When the temperature is small compared to the trap depth ($\xi =k_{B}T/U_0\ll 1$), there exists a range of timescales over which physical observables remain practically constant. This range can be very long, of the order of the Arrhenius factor $e^{1/\xi }$. For these quasiequilibrium states, the usual Boltzmann-Gibbs recipe does not work since the partition function is divergent due to the flatness of the potential at long distances. However, we show that the standard Boltzmann-Gibbs statistical framework and thermodynamic relations can still be applied through proper regularization. This can be a valuable tool for the analysis of metastability in the nonconfining potential fields that characterize a vast number of systems.

By numerically exact calculations of spin-1/2 antiferromagnetic Heisenberg models on small clusters up to 24 sites, we demonstrate that quantum entanglement between subsystems $A$ and $B$ in a pure ground state of a whole system $A+B$ can induce thermal equilibrium in subsystem $A$. Here, the whole system is bipartitoned with the entanglement cut that covers the entire volume of subsystem $A$. An effective temperature ${\mathcal{T}}_A$ of subsystem $A$ induced by quantum entanglement is not a parameter but can be determined from the entanglement von Neumann entropy ${\mathcal{S}}_A$ and the total energy ${\mathcal{E}}_A$ of subsystem $A$ calculated for the ground state of the whole system. We show that temperature ${\mathcal{T}}_A$ can be derived by minimizing the relative entropy for the reduced density matrix operator of subsystem $A$ and the Gibbs state (i.e., thermodynamic density matrix operator) of subsystem $A$ with respect to the coupling strength between subsystems $A$ and $B$. Temperature ${\mathcal{T}}_A$ is essentially identical to the thermodynamic temperature, for which the entropy and the internal energy evaluated using the canonical ensemble in statistical mechanics for the isolated subsystem $A$ agree numerically with the entanglement entropy ${\mathcal{S}}_A$ and the total energy ${\mathcal{E}}_A$ of subsystem $A$. Fidelity calculations ascertain that the reduced density matrix operator of subsystem $A$ for the pure but entangled ground state of the whole system $A+B$ matches, within a maximally $1.5\%$ error in the finite size clusters studied, the thermodynamic density matrix operator of subsystem $A$ at temperature ${\mathcal{T}}_A$, despite that these density-matrix operators are different in general. We also find that temperature ${\mathcal{T}}_A$ evaluated from the ground state of the whole system depends insignificantly on the system sizes, which is consistent with the fact that the thermodynamic temperature is an intensive quantity. We argue that quantum fluctuation in an entangled pure state can mimic thermal fluctuation in a subsystem. We also provide two simple but nontrivial analytical examples of free bosons and free fermions for which the two density-matrix operators are exactly the same if the effective temperature ${\mathcal{T}}_A$ is adopted. We furthermore discuss implications and possible applications of our finding.

The contribution of bulk and surface to the electrical resistance along crystallographic $b$ and $c$ axes as a function of crystal thickness gives evidence for temperature-independent surface states in an antiferromagnetic narrow-gap semiconductor ${\mathrm{CrSb}}_2$. Angle-resolved photoemission spectroscopy shows a clear electronlike pocket in the $\mathrm{\Gamma }-Z$ direction which is absent in the bulk band structure. First-principles calculations also confirm the existence of metallic surface states inside the bulk gap. Whereas combined experimental probes point to enhanced surface conduction similar to topological insulators, surface states are trivial since ${\mathrm{CrSb}}_2$ exhibits no band inversion.

Benchmarking numerical methods in quantum chemistry is one of the key opportunities that quantum simulators can offer. Here, we propose an analog simulator for discrete two-dimensional quantum chemistry models based on cold atoms in optical lattices. We first analyze how to simulate simple models, such as the discrete versions of H and ${\mathrm{H}}_2^{+}$, using a single fermionic atom. We then show that a single bosonic atom can mediate an effective Coulomb repulsion between two fermions, leading to the analog of molecular hydrogen in two dimensions. We extend this approach to larger systems by introducing as many mediating atoms as fermions, and derive the effective repulsion law. In all cases, we analyze how the continuous limit is approached for increasing optical lattice sizes.

A global symmetry (0-symmetry) in an $n$-dimensional space acts on the whole space. A higher symmetry acts on closed submanifolds (i.e., loops and membranes, etc.), and those transformations form a higher group. In this paper, we introduce the notion of algebraic higher symmetry, which generalizes higher symmetry and is beyond higher group. We show that an algebraic higher symmetry in a bosonic system in $n$-dimensional space is characterized and classified by a local fusion $n$-category. We find that, when restricted to its symmetric sub-Hilbert space, an algebraic higher symmetry can be fully characterized by a noninvertible gravitational anomaly (i.e., a topological order in one higher dimension). Thus, we also refer to a noninvertible gravitational anomaly as categorical symmetry to stress its connection to symmetry. This provides a holographic and entanglement view of symmetries. For a system with a categorical symmetry, its gapped state must spontaneously break part (not all) of the symmetry, and the state with the full symmetry must be gapless. Using such a holographic point of view, we obtain (1) the gauging of the algebraic higher symmetry; (2) the classification of anomalies for an algebraic higher symmetry; (3) the equivalence between classes of systems, with different (potentially anomalous) algebraic higher symmetries or different sets of low-energy excitations, as long as they have the same categorical symmetry; and (4) the classification of gapped liquid phases for bosonic and/or fermionic systems with a categorical symmetry, as gapped boundaries of a topological order in one higher dimension (that corresponds to the categorical symmetry). This classification includes symmetry protected trivial (SPT) orders and symmetry enriched topological (SET) orders with an algebraic higher symmetry.

We present a spectral-theoretic approach to time-average statistical mechanics for general, nonequilibrium initial conditions. We consider the statistics of bounded, local additive functionals of reversible as well as irreversible ergodic stochastic dynamics with continuous or discrete state-space. We derive exact results for the mean, fluctuations, and correlations of time-average observables from the eigenspectrum of the underlying generator of Fokker-Planck or master equation dynamics, and we discuss the results from a physical perspective. Feynman-Kac formulas are rederived using Itô calculus and combined with non-Hermitian perturbation theory. The emergence of the universal central limit law in a spectral representation is shown explicitly on large-deviation timescales. For reversible dynamics with equilibrated initial conditions, we derive a general upper bound to fluctuations of occupation measures in terms of an integral of the return probability. Simple, exactly solvable examples are analyzed to demonstrate how to apply the theory. As a biophysical example, we revisit the Berg-Purcell problem on the precision of concentration measurements by a single receptor. Our results are directly applicable to a diverse range of phenomena underpinned by time-average observables and additive functionals in physical, chemical, biological, and economical systems.

Short-time filtering of the photoionization amplitude extracted straight from the numerical solution of the time-dependent Schrödinger equation (TDSE) is used to identify dominant pathways that form photoelectron spectra in strong fields. Thereby, the “black-box nature” of TDSE solvers only giving the final spectrum is overcome, and simpler approaches, e.g., semiclassical based on the strong-field approximation, can be tested and improved. The approach also allows to suppress intercycle quantum interference between pathways removing patterns that are usually washed out in experiments.

In density functional–theoretic studies of photoionized water-based systems, the role of charge localization in proton-transfer dynamics is not well understood. This is due to the inherent complexity in extracting the contributions of coupled electron-nuclear nonadiabatic dynamics in the presence of exchange and correlation functional errors. In this work we address this problem by simulating a model system of ionized linear H-bonded water clusters using real-time time-dependent density functional theory–based Ehrenfest dynamics. Our aim is to understand how self-interaction error in semilocal exchange and correlation functionals affects the probability of proton transfer. In particular, we show that the proton-transfer probability is largely underestimated for short H-bonded chains but becomes comparable to that predicted by hybrid functionals for ${\left({\mathrm{H}}_2\mathrm{O}\right)}_n^{+}$ chains with $n>3$. This is because the formation of hemibonded-type geometries is largely suppressed in extended H-bonded structures. We also show how the degree of localization of the initial photo-hole is connected to the probability of a proton-transfer reaction, as well as to the hole–proton separation. These results are compared to those obtained with adiabatic dynamics where the initial wave function is allowed to relax to the ground state of the ion cluster, explaining why different functionals and dynamical approaches lead to quantitatively different results.

Violation of parity symmetry gives rise to various physical phenomena such as nonlinear transport and cross-correlated responses. In particular, the nonlinear conductivity has been attracting a lot of attentions in spin-orbit coupled semiconductors, superconductors, topological materials, and so on. In this paper we present a theoretical study of the nonlinear conductivity in odd-parity magnetic multipole ordered systems whose $\mathcal{PT}$ symmetry is essentially distinct from the previously studied acentric systems. Combining microscopic formulation and symmetry analysis, we classify the nonlinear responses in the $\mathcal{PT}$-symmetric systems as well as $\mathcal{T}$-symmetric (nonmagnetic) systems, and uncover nonlinear conductivity unique to the odd-parity magnetic multipole systems. A giant nonlinear Hall effect, nematicity-assisted dichroism, and magnetically induced Berry curvature dipole effect are proposed and demonstrated in a model for Mn-based magnets.

Ultrafast laser irradiation of silicon can significantly modify charge densities and optical indices, impacting the formation and the development of nanoscale-arranged periodic structures. Photoexcitation degree as well as thermodynamic, hydrodynamic, and structural aspects are reported for crossed orientation of laser-induced periodic surface structures generated on single-crystal silicon after multiple-pulse femtosecond laser irradiation. The periodic topography and microstructure generated by light scattering on surface nanoroughness were characterized to gain insights into the regime of photoexcitation, subsequent thermodynamic conditions, and inhomogeneous energy deposition related to periodic nanostructure formation and growth. A generated free-carrier density around $(3\pm 2)\times {10}^{21}{\mathrm{cm}}^{-3}$ is estimated from time-resolved ellipsometry and supported by time-dependent density-functional theory calculations. A finite-difference time-domain solution of the far-field interference of the surface scattered light and the refracted laser wave confirms the periodically crossed energy deposition for this excitation degree. The interference process does not necessarily involve surface plasmon polaritons, and quasicylindrical evanescent waves are identified as plausible scattered waves requiring less restrictive conditions of photoexcitation. Ab initio calculations are also performed to evaluate the transient state of silicon under strong electron-phonon nonequilibrium upon fs laser irradiation. For the reached excitation degree, an electron temperature up to 8000 K is deduced, supporting local amorphization processes observed as a result of high mechanical stress and quenching rates. Ab initio combined with electromagnetic calculations agree well with the results of topography and structural characterization.

We show that stimulated Raman adiabatic passage (STIRAP) and its superadiabatic version (saSTIRAP) have a natural geometric two-star representation on the Majorana sphere. In the case of STIRAP, we find that the evolution is confined to a vertical plane. A faster evolution can be achieved in the saSTIRAP protocol, which employs a counterdiabatic Hamiltonian to nullify the nonadiabatic excitations. We derive this Hamiltonian in the Majorana picture, and we observe how, under realistic experimental parameters, the counterdiabatic term corrects the trajectory of the Majorana stars toward the dark state. We also introduce a spin-1 average vector and present its evolution during the two processes, demonstrating that it provides a measure of nonadiabaticity. We show that the Majorana representation can be used as a sensitive tool for the detection of process errors due to ac Stark shifts and nonadiabatic transitions. Finally, we provide an extension of these results to mixed states and processes with decoherence.

Modern biological techniques such as Hi-C permit one to measure probabilities that different chromosomal regions are close in space. These probabilities can be visualized as matrices called contact maps. In this paper, we introduce a multifractal analysis of chromosomal contact maps. Our analysis reveals that Hi-C maps are bifractal, i.e., complex geometrical objects characterized by two distinct fractal dimensions. To rationalize this observation, we introduce a model that describes chromosomes as a hierarchical set of nested domains and we solve it exactly. The predicted multifractal spectrum is in excellent quantitative agreement with experimental data. Moreover, we show that our theory yields a more robust estimation of the scaling exponent of the contact probability than existing methods. By applying this method to experimental data, we detect subtle conformational changes among chromosomes during differentiation of human stem cells.

Amorphous solids, confined on the nanoscale, are studied using molecular dynamics computer simulation. Unlike in bulk samples, failure patterns in such systems are strongly affected by the confinement geometry and interfacial effects in the sample. We study a confined model glass, subjected to uniaxial loading, for varying aspect ratios of the sample geometry. While for a small aspect ratio, the sample breaks by forming a neck, above a critical value of the aspect ratio, cavitation is seen. The critical aspect ratio is associated with a strain-rate- and temperature-dependent critical curvature of the neck, above which the free energy of the system is minimized by the formation of a cavity. This mechanism of cavity formation is probably a generic mechanism for material's failure in small confined systems under mechanical load.

We present a theory of a hybrid quantum liquid state, the quantum spin-dipole liquid (QSDL), in a hydrogen-bonded electron system, by combining a quantum proton ice and Anderson's resonating valence bond spin liquid theory, motivated by the recent experimental discovery of a quantum spin liquid with proton fluctuations in $\kappa \text{−}{\mathrm{H}}_3{\left(\mathrm{Cat}\text{−}\mathrm{E}\mathrm{D}\mathrm{T}\text{−}\mathrm{T}\mathrm{T}\mathrm{F}\right)}_2$ (a.k.a. H-Cat). In our theory, an electron spin liquid and a proton dipole liquid are realized simultaneously in the ground state called quantum valence bond ice. In this state, neither of them can be established independently of the other. Analytical and numerical calculations reveal that this state has a large entanglement entropy between spins and dipoles, which is far beyond the (crude) Born-Oppenheimer approximation. We also examine the stability of QSDL with respect to perturbations and discuss implications for experiments in H-Cat and its deuterated analog D-Cat.

Ozone in Earth's atmosphere is known to have a radiative forcing effect on climate. Motivated by geochemical evidence for one or more nearby supernovae about 2.6 million years ago, we have investigated the question of whether a supernova at about 50 pc could cause a change in Earth's climate through its impact on atmospheric ozone concentrations. We used the “Planet Simulator” (plasim) intermediate-complexity climate model with prescribed ozone profiles taken from existing atmospheric chemistry modeling. We found that the effect on globally averaged surface temperature is small, but localized changes are larger and differences in atmospheric circulation and precipitation patterns could have regional impacts.

Open classical and quantum systems with effective parity-time ($\mathcal{PT}$) symmetry, over the past five years, have shown tremendous promise for advances in lasers, sensing, and nonreciprocal devices. And yet, how such effective $\mathcal{PT}$-symmetric non-Hermitian models emerge out of Hermitian quantum mechanics is not well understood. Here, starting from a fully Hermitian microscopic Hamiltonian description, we show that a non-Hermitian Hamiltonian emerges naturally in a double-quantum-dot (DQD) circuit-QED setup, which can be controllably tuned to the $\mathcal{PT}$-symmetric point. This effective Hamiltonian governs the dynamics of two coupled circuit-QED cavities with a voltage-biased DQD in one of them. Our analysis also reveals the effect of quantum fluctuations on the $\mathcal{PT}$-symmetric system. The $\mathcal{PT}$ transition is, then, observed both in the dynamics of cavity observables as well as via an input-output experiment. As a simple application of the $\mathcal{PT}$ transition in this setup, we show that loss-induced enhancement of amplification and lasing can be observed in the coupled cavities. By comparing our results with two conventional local Lindblad equations, we demonstrate the utility and limitations of the latter. Our results pave the way for an on-chip realization of a potentially scalable non-Hermitian system with a gain medium in the quantum regime, as well as its potential applications for quantum technology.

Ultracold gases of dipolar Dy have emerged as platforms where studying novel phases of matter, such as liquid droplets, poses many questions since standard theoretical methods fail to account for some of their observed properties. Here we investigate the self-bound states of dipolar Dy condensates by using general Gaussian-state ansatzes which go beyond conventional coherent-state ansatzes by including multimode squeezing. Our theory provides a transition between self-bound liquid and gas phases that agrees well with experimental observations and additionally reveals an experimentally unexplored transition in the self-bound gas region from a coherent-dominated to a squeezed-dominated phase. Our theory also allows one to extract the real part of the three-body interaction strength of the Dy atoms from the particle number distribution of the condensates. This allows us to show that the self-bound states are stabilized by the short-range three-body repulsion. Our study sheds a different light onto the properties of self-bound droplets of Bose-Einstein condensates.