In 1949, Ramsey's method [Phys. Rev. 76, 996 (1949)] of separated oscillating fields was elaborated boosting over many decades metrological performances of atomic clocks and becoming the standard technique for very high-precision spectroscopic measurements. A generalization of this interferometric method is presented replacing the two single coherent excitations by arbitrary composite laser pulses. The rotation of the state vector of a two-level system under the effect of a single pulse is described using the Pauli matrices basis of the SU(2) group. It is then generalized to multiple excitation pulses by a recursive Euler-Rodrigues-Gibbs algorithm describing a composition of rotations with different rotation axes. A general analytical formula for the phase shift associated with the clock's interferometric signal is derived. As illustrations, hyper-clocks based on three-pulse and five-pulse interrogation protocols are studied and shown to exhibit nonlinear cubic and quintic sensitivities to residual probe-induced light shifts. The presented formalism is well suited to optimize composite phase shifts produced by tailored quantum algorithms in order to design a new generation of optical frequency standards and robust engineering control of atomic interferences in atomic, molecular, and optical physics with cold matter and antimatter.

Microscopically, the cold liquid around freezing consists of crystalline ordered domains supporting thermally excited acoustic wave turbulence. Whether and how the above uncertain multiscale waves can lead to uncertain avalanche microstructure rearrangements in the form of multiscale clusters, and identifying their precursors, are elusive fundamental issues. Here, using a cold quasi-two-dimensional dusty plasma liquid as a platform, we experimentally address the above issues, especially the extreme avalanche activities, by correlating avalanche dynamics with the spatiotemporal evolutions of local structural order, defects, and the local amplitudes and phases of various wave modes. It is found that the preceding larger skeleton of poor structural order around more and widely spread defects can facilitate the later sequential multiscale wave excitations from slow to fast modes and their cascaded intermittent phase synchronizations for bond-breaking/reconnection and structural rearrangements. It is the key for the onset, spreading with defect propagation, and termination of the large avalanche cluster.

A deeper theoretical understanding of driven-dissipative interacting systems and their nonequilibrium phase transitions is essential both to advance our fundamental physics understanding and to harness technological opportunities arising from optically controlled quantum many-body states. This paper provides a numerical study of dynamical phases and the transitions between them in the nonequilibrium steady state of the prototypical two-dimensional Heisenberg antiferromagnet with drive and dissipation. We demonstrate a nonthermal transition that is characterized by a qualitative change in the magnon distribution from subthermal at low drive to a generalized Bose-Einstein form including a nonvanishing condensate fraction at high drive. A finite-size analysis reveals static and dynamical critical scaling at the transition, with a discontinuous slope of the magnon number versus driving field strength and critical slowing down at the transition point. Implications for experiments on quantum materials and polariton condensates are discussed.

In search of materials with three-dimensional flat band dispersions, using ab initio computations we investigate how topological phases evolve as a function of hydrostatic pressure and uniaxial strain in two types of superlattices: HgTe/CdTe and HgTe/HgSe. In short-period HgTe/CdTe superlattices, our analysis unveils the presence of isoenergetic nodal lines, which could host strain-induced three-dimensional flat bands at the Fermi level without requiring doping, when fabricated, for instance, as core-shell nanowires. In contrast, HgTe/HgSe short-period superlattices are found to harbor a rich phase diagram with a plethora of topological phases. Notably, the unstrained superlattice realizes an ideal Weyl semimetal with Weyl points situated at the Fermi level. A small-gap topological insulator with multiple band inversions can be obtained by tuning the volume: under compressive uniaxial strain, the material transitions sequentially into a Dirac semimetal to a nodal-line semimetal, and finally into a topological insulator with a single band inversion.

Phase gratings, each period of which consists of even numbers of equal-width and equal-thickness elements, can be devised to attain asymmetric diffraction patterns. We show that engineering of offset refractive indices in different elements exhibiting a spatially odd symmetry leads to the elimination of a single diffraction order (directional elimination), while further manipulations on offset refractive indices may lead to the elimination of all odd or even orders (grouped elimination) or all orders but one or two selected (directional selection). These intriguing effects arise from destructive interference between diffracted amplitudes contributed by paired or successive elements, and violation of Friedel's law in such transparent gratings is an effect of higher order multiple scattering.

In a layered and strongly anisotropic superconductor, the hybrid modes provided by the propagation of electromagnetic waves in the matter identify two well-separated energy scales connected to the large in-plane plasma frequency and to the soft out-of-plane Josephson plasmon. Despite wide interest in their detection and manipulation by means of different experimental protocols, the physical ingredients underlying a unified description of plasma waves valid at arbitrary energy and momentum are still poorly understood. Here we provide a complete description of generalized plasma waves in layered superconductors in terms of the gauge-invariant superconducting phase by including both the Coulomb interaction and the relativistic effects. We show that the anisotropy of the superfluid response leads to two intertwined hybrid light-matter modes with mixed longitudinal and transverse character, while a purely longitudinal plasmon is only recovered for wave vectors larger than the crossover scale set in by the plasma-frequency anisotropy. Interestingly, below such scale both modes appear with equal weight in the physical density response. Our results open a promising perspective for plasmonic applications made possible by next-generation spectroscopic techniques able to combine submicron momentum resolution with THz energy resolution.

We study the creation of quantum skyrmions in quadratic nanoscopic lattices of quantum spins coupled by Dzyaloshinkii-Moriya and exchange interactions. We numerically show that different kinds of quantum skyrmions, characterized by the magnitude of their spin expectation values and strong differences in their stability, can appear as ground state and as metastable excitations. In dependence on the coupling strengths and the lattice size, the adiabatic rotation of magnetic control fields at the boundary allows for the creation of quantum skyrmions.

To understand general properties of creep failure with healing effects, we study a mean-field fiber bundle model with probabilistic rupture and rejoining processes. The dynamics of the model is determined by two factors: bond breaking and formation of new bonds. Steady states are realized due to the balance between breaking and healing beyond a critical healing factor, below which the bundle breaks completely. Correlation between the fluctuating value of strain generated in the model with time at the steady state leads to a characteristic time that diverges in a scale-free manner as we approach the critical healing factor. Transient behaviors in the strain rate also involve a power law with a nonuniversal exponent.

The ruthenate family of layered perovskites has been a topic of intense interest, with much work dedicated to the superconducting state of ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$. Another long-standing puzzle is the lack of superconductivity in its sister compound, ${\mathrm{Sr}}_3{\mathrm{Ru}}_2{\mathrm{O}}_7$, which constrains the possible mechanisms of ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$. Here we address a microscopic mechanism that unifies the orders in these materials. Beginning from a model of ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ featuring interorbital spin-triplet pairing via Hund's and spin-orbit couplings, we find that bilayer coupling alone enhances, while staggered rotations destroy interorbital superconductivity. A magnetic field then shifts van Hove singularities, allowing intraorbital spin-density wave order to form in ${\mathrm{Sr}}_3{\mathrm{Ru}}_2{\mathrm{O}}_7$. Our theory predicts that ${\mathrm{Sr}}_3{\mathrm{Ru}}_2{\mathrm{O}}_7$ without staggered rotations exhibits interorbital superconductivity with a possibly higher transition temperature.

Charge-transfer insulators are the parent phase of a large group of today's unconventional high-temperature superconductors. Here we study experimentally and theoretically the interband excitations of the charge-transfer insulator silver fluoride ${\mathrm{AgF}}_2$, which has been proposed as an excellent analog of oxocuprates. Optical conductivity and resonant inelastic x-ray scattering on ${\mathrm{AgF}}_2$ polycrystalline sample show a close similarity with that measured on undoped ${\mathrm{La}}_2{\mathrm{CuO}}_4$. While the former shows a charge-transfer gap $\sim 3.4$ eV, larger than in the cuprate, $dd$ excitations are nearly at the same energy in the two materials. Density functional theory and exact diagonalization cluster computations of the multiplet spectra show that ${\mathrm{AgF}}_2$ is more covalent than the cuprate, in spite of the larger fundamental gap. Furthermore, we show that ${\mathrm{AgF}}_2$ is at the verge of a charge-transfer instability. The overall resemblance of our data on ${\mathrm{AgF}}_2$ to those published previously on ${\mathrm{La}}_2{\mathrm{CuO}}_4$ suggests that the underlying charge-transfer insulator physics is the same, while ${\mathrm{AgF}}_2$ could also benefit from a proximity to a charge density wave phase as in ${\mathrm{BaBiO}}_3$. Therefore, our work provides a compelling support to the future use of fluoroargentates for materials' engineering of novel high-temperature superconductors.

Error correcting codes with a universal set of transversal gates are a desideratum for quantum computing. Such codes, however, are ruled out by the Eastin-Knill theorem. Moreover, the theorem also rules out codes which are covariant with respect to the action of transversal unitary operations forming continuous symmetries. In this work, starting from an arbitrary code, we construct approximate codes which are covariant with respect to the entire group of local unitary gates in dimension $d(<\infty )$, using quantum reference frames. We show that our codes are capable of efficiently correcting different types of erasure errors. When only a small fraction of the $n$ qudits upon which the code is built are erased, our covariant code has an error that scales as $1/n^2$, which is reminiscent of the Heisenberg limit of quantum metrology. When every qudit has a chance of being erased, our covariant code has an error that scales as $1/n$. We show that the error scaling is optimal in both cases. Our approach has implications for fault-tolerant quantum computing, reference frame error correction, and the AdS-CFT duality.

We propose a correspondence between the description of emergent Lorentz symmetry in condensed-matter systems and the established general effective field theory for Lorentz violation in fundamental theories of spacetime and matter. This correspondence has potential implications in both directions. We illustrate the proposal by investigating its consequences for the spectral and transport properties of Dirac and Weyl semimetals. Particular realizations of this framework give rise to Dirac nodal spectra with nodal lines and rings. We demonstrate a bulk-boundary correspondence between bulk topological invariants and drumhead surface states of these Dirac nodal semimetals. We calculate their transport coefficients in leading-order perturbation theory, thereby characterizing the unconventional electromagnetic response due to small deviations from emergent Lorentz invariance. Some prospective future applications of the correspondence are outlined.

Bacteria suspended in fluids swim collectively and display fascinating emergent dynamics. Although bacterial collective swimming in bulk suspensions has been well studied, its counterpart in confined two-dimensional (2D) geometries relevant to many natural habitats of bacteria is still poorly understood. Here, through carefully designed experiments on Escherichia coli in a Hele-Shaw geometry, we show that a small change in the degree of confinement leads to a drastic change in bacterial collective swimming. While a long-range nematic order emerges for bacteria that can cross over each other during encounters, a slight decrease of the confining height that prevents the crossing leads to the formation of bacterial clusters with a short-range polar order. By tracking the swimming kinetics of individual bacteria, we reveal the microscopic origins of the two emergent collective phases and illustrate the effect of the collective dynamics on the swimming behaviors of single bacteria. Our study provides insights into bacterial collective swimming under confinement and demonstrates a simple way to control the emergent symmetry of collective phases.

The classical spin-vector Monte Carlo (SVMC) model is a reference benchmark for the performance of a quantum annealer. Yet, as a Monte Carlo method, SVMC is unsuited for an accurate description of the annealing dynamics in real-time. We introduce the spin-vector Langevin (SVL) model as an alternative benchmark in which the time evolution is described by Langevin dynamics. The SVL model is shown to provide a more stringent test than the SVMC model for the identification of quantum signatures in the performance of quantum annealing devices, as we illustrate by describing the Kibble-Zurek scaling associated with the dynamics of symmetry breaking in the transverse field Ising model, recently probed using D-Wave machines. Specifically, we show that D-Wave data are reproduced by the SVL model.

Quantifying the nonuniversal three-body losses in ultracold atomic gases has been a long-standing problem. We go beyond earlier approaches to solve this problem by using a model that includes realistic pairwise interaction potentials and the exact three-atom spin structure. With this model we can successfully explain experimental observations for weakly interacting ${}^7\mathrm{Li}$ and ${}^{87}\mathrm{Rb}$ atoms. Capturing the exact spin structure, we are able to reveal a strong three-body spin-exchange recombination mechanism. In addition, we predict a regime of low three-body recombination rate in the ${}^7\mathrm{Li}$ system that is advantageous for a variety of many-body experiments. This work opens avenues to study spin-involved few-body processes in quantum gases.