${\mathrm{CeRh}}_2{\mathrm{As}}_2$, a nonsymmorphic heavy fermion material, was recently reported to host a remarkable temperature versus $z$-axis magnetic-field phase diagram with two superconducting phases. In this material, the two inequivalent Ce sites per unit cell, related by inversion symmetry, introduce a sublattice structure corresponding to an extra internal degree of freedom. Here we propose a classification of the possible superconducting states in ${\mathrm{CeRh}}_2{\mathrm{As}}_2$ from the two Ce-sites' perspective. Based on the superconducting fitness analysis and the quasiclassical Eilenberger equations, we discuss two limits: Rashba spin-orbit coupling and interlayer hopping dominated normal state. In both limits, we are able to find two scenarios that generate phase diagrams in qualitative agreement with experiments: (i) intrasublattice pairing with an even-odd transition under $z$-axis magnetic field and (ii) intersublattice pairing with an odd-odd transition under $z$-axis magnetic field.

We explore the effectiveness of variational quantum circuits in simulating the ground states of quantum many-body Hamiltonians. We show that generic high-depth circuits, performing a sequence of layer unitaries of the same form, can accurately approximate the desired states. We demonstrate their universal success by using two Hamiltonian systems with very different properties: the transverse field Ising model and the Sachdev-Ye-Kitaev model. The energy landscape of the high-depth circuits has a proper structure for the gradient-based optimization, i.e., the presence of local extrema—near any random initial points—reaching the ground level energy. We further test the circuit's capability of replicating random quantum states by minimizing the Euclidean distance.

In a recent paper [J. Kullig, X. Jiang, L. Yang, and J. Wiersig, Phys. Rev. Res. 2, 012072(R) (2020)], the authors reported on an alternative concept to confine light in a microdisk cavity which is based on sequential transmissions at Brewster's angle. In this paper, we combine that approach with the traditional concept of whispering-gallery microcavities which utilize total internal reflection. This allows for a notched cavity design promoting high-$Q$ modes which are conventionally excitable via an attached waveguide and have a considerable fraction of the intensity confined in the notch. The interesting mode characteristics as well as the excellent sensing capability of the Brewster notched cavity is discussed. A further enhancement in the sensitivity is achieved via the utilization of an exceptional point.

The Casimir effect arises from the zero-point energy of particles in momentum space deformed by the existence of two parallel plates. For degrees of freedom on the lattice, its energy-momentum dispersion is determined so as to keep a periodicity within the Brillouin zone, so that its Casimir effect is modified. We study the properties of Casimir effect for lattice fermions, such as the naive fermion, Wilson fermion, and overlap fermion based on the Möbius domain-wall fermion formulation, in the $1+1-$, $2+1-$, and $3+1$-dimensional space-time with the periodic or antiperiodic boundary condition. An oscillatory behavior of Casimir energy between odd and even lattice size is induced by the contribution of ultraviolet-momentum (doubler) modes, which realizes in the naive fermion, Wilson fermion in a negative mass, and overlap fermions with a large domain-wall height. Our findings can be experimentally observed in condensed matter systems such as topological insulators and also numerically measured in lattice simulations.

We introduce a class of hybrid quantum circuits, with random unitaries and projective measurements, which host long-range order in the area-law entanglement phase of the steady state. Our primary example is circuits with unitaries respecting a global Ising symmetry and two competing types of measurements. The phase diagram has an area-law phase with spin-glass order, which undergoes a direct transition to a paramagnetic phase with volume-law entanglement, as well as a critical regime. Using mutual information diagnostics, we find that such entanglement transitions preserving a global symmetry are in universality classes different from those without symmetry. We analyze generalizations of such hybrid circuits to higher dimensions, which allow for coexistence of order and volume-law entanglement, as well as topological order without any symmetry restrictions.

A pair-density-wave state has been suggested to exist in underdoped cuprate superconductors, with some supporting experimental evidence emerging over the past few years from scanning tunneling spectroscopy. Several studies have also linked the observed quantum oscillations in these systems to a reconstruction of the Fermi surface by a pair-density wave. Here, we show, using semiclassical analysis and numerical calculations, that a Fermi pocket created by first-order scattering from a pair-density wave cannot induce such oscillations. In contrast, pockets resulting from second-order scattering can cause oscillations. We consider the effects of a finite pair-density-wave correlation length on the signal, and demonstrate that it is only weakly sensitive to disorder in the form of $\pi$-phase slips. Finally, we discuss our results in the context of the cuprates and show that a bidirectional pair-density wave may produce observed oscillation frequencies.

Mass conservation in chemical species appears in a broad class of reaction-diffusion systems (RDSs) and is known to cause coarsening of the pattern in chemical concentration. Recent theoretical studies on RDSs with mass conservation (MCRDSs) have reported that the interfacial curvature between two states contributes to the coarsening process, which is reminiscent of phase separation phenomena. However, since MCRDSs do not presuppose a variational principle, it is largely unknown whether description of surface tension is operative. In this paper, we numerically and theoretically explore the coarsening process of patterns in MCRDSs in two and three dimensions. We identify the parameter regions where the homogeneous steady state becomes stable, unstable, and metastable. In the unstable region, pattern formation is triggered by usual $\left(\text{type}\text{−}{\mathrm{II}}_{\mathrm{s}}\right)$ instability, whereas in the metastable region, nucleation-growth-type pattern formation is observed. In the later stage, spherical droplet patterns are observed in both regions, where they obey a relation similar to the Young-Laplace law and coarsen following the evaporation-condensation mechanism. These results demonstrate that in the presence of a conserved variable, a physical quantity similar to surface tension is relevant to RDSs, which provides insight into molecular self-assembly driven by chemical reactions.

We present a detailed analysis of the relaxation dynamics in an extended bosonic Josephson junction. We show that stochastic classical field simulations using Gross-Pitaevskii equations in three spatial dimensions reproduce the main experimental findings of Pigneur et al. [Phys. Rev. Lett. 120, 173601 (2018)]. We give an analytic solution describing the short time evolution through multimode dephasing. For longer times, the observed relaxation to a phase-locked state is caused by nonlinear dynamics beyond the sine-Gordon model, induced by the longitudinal confinement potential and persisting even at zero temperature. Finally, we analyze different experimentally relevant trapping geometries to mitigate these effects. Our results provide the basis for future experimental implementations aiming to study nonlinear and quantum effects of the relaxation in extended bosonic Josephson junctions.

In this work we are concerned with the understanding of the collisionless drag or entrainment between two superfluids, also called Andreev-Bashkin effect, in terms of current response functions. The drag density is shown to be proportional to the cross transverse current-current response function, playing the role of a normal component for the single-species superfluid density. We can in this way link the existence of finite entrainment with the exhaustion of the energy-weighted sum rule in the spin channel. The formalism is then used to reproduce some known results for a weakly interacting Bose-Bose mixture. We include the drag effect to determine the beyond mean-field correction on the speed of sound and on the spin dipole excitations for a homogeneous and a trapped weakly interacting gas, respectively. Finally, we show that the response to a quick dipole perturbation on one of the species induces a dipole moment on the other species which is proportional to the drag at short times.

We study superconductivity in a family of one-dimensional incommensurate systems with $s$-wave pairing interaction. The incommensurate potential can alter the spatial characteristics of electrons in the normal state, leading to either extended, critical, or localized wave functions. We find that superconductivity is significantly enhanced when the electronic wave function exhibits a critical multifractal structure. This criticality also manifests itself in the power-law dependence of the superconducting temperature on the pairing strength. As a consequence, an extended superconducting dome is expected to exist around the localization-delocalization transition, which can be induced by either tuning the amplitude of the incommensurate potential or by varying the chemical potential across a mobility edge. Our results thus suggest a different approach to enhance the superconducting transition temperature through engineering of the incommensurate potential.

We propose a class of lattice models realizable in a wide range of setups whose low-energy dynamics exactly reduces to Dirac fields subjected to ($1+1$)-dimensional [($1+1$)D] gravitational backgrounds, including (anti-)de Sitter space-time. Wave packets propagating on the lattice exhibit an eternal slowdown for power-law position-dependent hopping integrals $t\left(x\right)\propto x^{\gamma }$ when $\gamma \ge 1$, signaling the formation of black hole event horizons. For $\gamma <1$ instead the wave packets behave radically different and bounce off the horizon. We show that the eternal slowdown relates to a zero-energy spectral singularity of the lattice model and that the semiclassical wave packets trajectories coincide with the geodesics on ($1+1$)D dilaton gravity, paving the way for new and experimentally feasible routes to mimic black hole horizons and realize ($1+1$)D space-times as they appear in certain gravity theories.

The performance of endoreversible thermal machines operating at finite power constitutes one of the main challenges of nonequilibrium classical and quantum thermodynamics, engineering, and others. We introduce the idea of adjusting the interaction time asymmetry in order to optimize the engine performance. We consider one of the simplest thermal machines, composed of a quantum dot interacting sequentially with two different reservoirs of heat and particles. Distinct optimization protocols are analyzed in the framework of stochastic thermodynamics. Results reveal that asymmetric interaction times play a fundamental role in enhancing the power output and that maximizations can provide an increase of more than 25% compared with the symmetric case. As an extra advantage, efficiencies at maximum power are slightly greater than the endoreversible Curzon-Ahlborn efficiency for a broad range of reservoir temperatures.

In intense laser-plasma interactions, maximizing the density of fast electrons in the laser spot area is key to achieving plasma heating and particle acceleration. We find that when the laser spot size is large compared with the target foil thickness, fast electrons circulating in the foil show a “random walk” in the lateral direction due to the scattering by fluctuating fields at the plasma surface inside the spot area. We model the lateral motion as a diffusion, and find the resulting diffusion velocity is much slower than the speed of the ballistic transport. Hence, fast electrons accumulate in the spot region, and over time their density becomes typically 10 times greater than the laser-accelerated fast electron density. The enhancement of fast electron density in the target pushes the ion acceleration to more efficient regime.

We experimentally and theoretically investigate the field-free alignment of the asymmetric-top acetone molecule. Our study shows that the production of postpulse aligned molecules in dense samples (0.05–0.2 bar) of room-temperature acetone using a single-pulse excitation can be significantly improved by rotational alignment echoes induced in a two-pulse excitation scheme. We report the observation of fractional echoes that can be used to reveal the nonlinearity of the molecular system. In a proof-of-principle experiment, a prealigned sample of acetone is also used for third-harmonic generation. The analysis of the experimental data with numerical simulations based on quantum and classical models enables the determination of the collisional decay rate of acetone alignment, as well as a test of the static, second-order, electric hyperpolarizabilities of the molecule derived from ab initio calculations presented in this work.

Ultrafast x-ray imaging is useful for diagnosing a wide range of nanosecond-time scale physical processes, particularly those concealed by optical emission or otherwise opaque objects. Here we use the ultrafast x-ray imaging facilities at Argonne National Laboratory's Advanced Photon Source to interrogate nanosecond-pulsed single-electrode plasma initiation processes in water ($+25$ kV, 10 ns, 5 mJ), with supporting nanosecond optical imaging and x-ray diffraction computational model. These results clearly resolve narrow ($\sim 10\mu \mathrm{m}$) low-density plasma channels during initiation time scales typically obscured by optical emission. This multiphase environment is not well described in literature, and these experimental results appear to be inconsistent with prevailing breakdown initiation hypotheses. This work also proposes this plasma process as a cheap, compact, and repeatable benchmark imaging target with hypersonic phenomena (29.1 km/s) and very high-power densities ($1\mathrm{TW}/{\mathrm{cm}}^2$), useful for the development of next-generation ultrafast imaging of inertial confinement fusion and other nanosecond processes of interest.

Synthetic materials that are auxetic (negative Poisson's ratio) at a molecular level have long been sought after. An auxetic liquid crystal elastomer (LCE) was reported recently, but the physical origin of the behavior has remained unclear. Here, we explain the physics behind the auxetic response of a uniaxial LCE under strain by the emergence of biaxial order. Our study relies on understanding order parameters (OPs), determined via Raman scattering, for LCEs strained either parallel or perpendicular to the director and explaining their relevance in terms of existing LCE theory. In particular, we consider a 3D interpretation of the orientational distribution function. We use uniaxial and biaxial models to deduce that (i) a changing nematic order drives the mechanical Fréedericksz transition (MFT), (ii) the apparent semi-soft elasticity exhibited by this LCE is related to this change in order, (iii) there is also an emergence of biaxial order in the LCE, and (iv) the emergence of biaxiality explains the auxetic response. Uniaxial OPs, $\langle P_{200}\rangle$ and $\langle P_{400}\rangle$, initially take values of 0.6 and 0.3 and, for strains parallel to the director, increase by 20%. For perpendicular strains, the OPs reduce dramatically with increasing strain, becoming zero at the MFT, where the director reorients to align with the strain axis; the auxetic behavior emerges in the same strain regime. Our explanation identifies key parameters in determining the requirements for auxetic behavior in LCEs.

We show that current noisy quantum computers are ideal platforms for the simulation of quantum many-body dynamics in generic open systems. We demonstrate this using the IBM Quantum Computer as an experimental platform for confirming the theoretical prediction from Wang et al., [Phys. Rev. Lett. 124, 100604 (2020)] of an emergent hierarchy of relaxation timescales of many-body observables involving different numbers of qubits. Using different protocols, we leverage the intrinsic dissipation of the machine responsible for gate errors, to implement a quantum simulation of generic (i.e., structureless) local dissipative interactions.

We propose a scenario of realizing the toric code phase, which can be potentially utilized for fault-tolerant quantum computation, in candidate materials of Kitaev magnets. It is demonstrated that four-body interactions among Majorana fermions in the Kitaev spin liquid state, which are induced by applied magnetic fields as well as non-Kitaev-type exchange interactions, trigger a nematic phase transition of Majorana bonds without magnetic orders, accompanying the change of the Chern number from $\pm 1$ to zero. This gapful spin liquid state with zero Chern number is simply the toric code phase. Our result potentially explains the topological nematic transition recently observed in $\alpha \text{−}{\mathrm{RuCl}}_3$ via heat capacity measurements (O. Tanaka et al., arXiv:2007.06757).

We computationally demonstrate a new method for coherently controlling the rotation-axis direction in asymmetric top molecules with an optical centrifuge. Appropriately chosen electric-field strengths and the centrifuge's acceleration rate allow to generate a nearly arbitrary rotational wave packet. For dihydrogen sulfide $\left({\text{D}}_2\text{S}\right)$ and 2H-imidazole $\left({\text{C}}_3{\text{H}}_4{\text{N}}_2\right)$, we created wave packets at large values of the rotational quantum number $J$ with the desired projections of the total angular momentum onto two of the molecules' principal axes of inertia. One application of the new method is three-dimensional alignment with a molecular axis aligned along the laser's wave vector, which is important for the three-dimensional imaging of molecules yet not accessible in standard approaches. The simultaneous orientation of the angular momentum in the laboratory frame and in the molecular frame could also be used in robust control of scattering experiments.

We obtain general inequalities constraining the difference between the average of an arbitrary function of a phenotypic trait, which includes the fitness landscape of the trait itself, in the presence or in the absence of natural selection. These inequalities imply bounds on the strength of selection, which can be measured from the statistics of trait values and divisions along lineages. The upper bound is related to recent generalizations of linear response relations in stochastic thermodynamics, and shares common features with Fisher's fundamental theorem of natural selection, and with its generalization by Price, although they define different measures of selection. The lower bound follows from recent improvements on Jensen's inequality, and both bounds depend on the variability of the fitness landscape. We illustrate our results using numerical simulations of growing cell colonies and with experimental data of time-lapse microscopy experiments of bacteria cell colonies.