We investigate squeezing of magnons in a conical spin spiral configuration. We find that while the energy of magnons propagating along the $\mathit{k}$ and the $-\mathit{k}$ directions can be different due to the nonreciprocal dispersion, these two modes are connected by the squeezing, and hence can be described by the same squeezing parameter. The squeezing parameter diverges at the center of the Brillouin zone due to the translational Goldstone mode of the system, but the squeezing also vanishes for certain wave vectors. We discuss possible ways of detecting the squeezing.

Trading activities in financial systems create various channels through which systemic risk can propagate. An important contagion channel is financial fire sales, where a bank failure causes asset prices to fall due to asset liquidation, which in turn drives further bank defaults, triggering the next rounds of liquidation. This process can be considered as a complex contagion, yet it cannot be modeled using the conventional binary-state contagion models because there is a continuum of states representing asset prices. Here, we develop a threshold model of continuous-state cascades in which the states of each node are represented by real values. We show that the solution of a multistate contagion model, for which the continuous states are discretized, accurately replicates the simulated continuous state distribution as long as the number of states is moderately large. This discretization approach allows us to exploit the power of approximate master equations to trace the trajectory of the fraction of defaulted banks and obtain the distribution of asset prices that characterize the dynamics of fire sales through overlapping portfolios. We examine the accuracy of the proposed method using real data on asset-holding relationships in exchange-traded funds. Our methodology could contribute to evaluating and controlling systemic risk that would emerge in various real-world networked systems in the form of continuous-state complex contagion.

The critical field behavior of a layered Ising superconductor with finite number of layers is studied. Under in-plane magnetic fields, the finite-momentum superconductivity dubbed as the orbital Fulde-Ferrell-Larkin-Ovchinnikov state is found in the regime of low field and high temperature. Our theory agrees well with the experimental results in Nature 619, 46 (2023).

Micromechanical resonator performance is fundamentally limited by the coupling to a thermal environment. The magnitude of this thermodynamical effect is typically considered in accordance with a physical temperature, assumed to be uniform across the resonator's physical span. However, in some circumstances, e.g., quantum optomechanics or interferometric gravitational wave detection, the temperature of the resonator may not be uniform, resulting in the resonator being thermally linked to a spatially varying thermal bath. In this case, the link of a mode of interest to its thermal environment is less straightforward to understand. Here, we engineer a distributed bath on a germane optomechanical platform—a phononic crystal—and utilize both highly localized and extended resonator modes to probe the spatially varying bath in entirely different bath regimes. As a result, we observe striking differences in the modes' Brownian motion magnitude. From these measurements we are able to reconstruct the local temperature map across our resonator and measure nanoscale effects on thermal conductivity and radiative cooling. Our work explains some thermal phenomena encountered in optomechanical experiments, e.g., mode-dependent heating due to light absorption. Moreover, our work generalizes the typical figure of merit quantifying the coupling of a resonator mode to its thermal environment from the mechanical dissipation to the overlap between the local dissipation and the local temperature throughout the resonator. This added understanding identifies design principles that can be applied to the performance of micromechanical resonators.

Nuclear isomers play a key role in the creation of the elements in the universe and potentially have significant applications related to the controlled release of nuclear energy on demand. Particularly, ${}^{93m}\mathrm{Mo}$ is a good candidate for studying the depletion of nuclear isomers via nuclear excitation by electron capture. Therefore, it is necessary to explore the efficient approach of ${}^{93m}\mathrm{Mo}$ production. In this paper, we experimentally demonstrate an efficient production of ${}^{93m}\mathrm{Mo}$ via ${}^{93}\mathrm{Nb}\left(p,n\right)$ reaction induced by an intense laser pulse. Employing the picosecond-duration, 100 J laser pulse, the ${}^{93m}\mathrm{Mo}$ isomer at 2425 keV ($21/2^{+}$, $T_{1/2}=6.85\mathrm{h}$) is generated with a high yield of $1.8\times {10}^6$ particles/shot. The resulting peak production efficiency reaches ${10}^{17}$ particles/s, which is at least five orders of magnitude higher than that obtained using the classical accelerator. The impacts of the production and destruction of ${}^{93m}\mathrm{Mo}$ to the astrophysical $p$-nuclide ${}^{92}\mathrm{Mo}$ are studied. It is found that the ${}^{93}\mathrm{Nb}\left(p,n\right){}^{93m}\mathrm{Mo}$ reaction is an important production path of ${}^{93m}\mathrm{Mo}$, which could further influence the production of ${}^{92}\mathrm{Mo}$. In addition, a direct measurement of the $(p,n)$ reaction rate is proposed using the laser-induced proton beam of which the energies follow the Maxwell-Boltzmann distribution well. It is believed that the laser-induced proton beam opens an avenue for the production of nuclear isomers with high peak efficiency used for the studies of $p$-nuclei nucleosynthesis.

Control of quantum matter through resonant electromagnetic cavities is a promising route towards establishing control over material phases and functionalities. Quantum paraelectric insulators—materials that are nearly ferroelectric—are particularly promising candidate systems for this purpose since they have strongly fluctuating collective modes that directly couple to the electric field. In this work, we explore this possibility in a system comprised of a quantum paraelectric sandwiched between two high-quality metal mirrors, realizing a Fabry-Perot-type cavity. By developing a full multimode, continuum description we are able to study the effect of the cavity in a spatially resolved way for a variety of system sizes and temperatures. Surprisingly, we find that once a continuum of transverse modes is included the cavity ends up suppressing ferroelectric correlations. This effect arises from the screening out of transverse photons at the cavity boundaries and, as a result, is confined to the surface of the paraelectric sample. We also explore the temperature dependence of this effect and find it vanishes at high temperatures, indicating it is a purely quantum mechanical effect. We connect our result to calculations of Casimir and Van der Waals forces, which we argue are closely related to the dipolar fluctuations in the quantum paraelectric. Our results are based on a general formalism and are expected to be widely applicable, paving the way towards studies of the quantum electrodynamics of heterostructures featuring multiple materials and phases.

Machine learning models capable of handling the large data sets collected in the financial world can often become black boxes expensive to run. The quantum computing paradigm suggests new optimization techniques that, combined with classical algorithms, may deliver competitive, faster, and more interpretable models. In this paper we propose a quantum-enhanced machine learning solution for the prediction of credit rating downgrades, also known as fallen-angels forecasting in the financial risk management field. We implement this solution on a neutral atom quantum processing unit with up to 60 qubits on a real-life data set. We report performance that is competitive with the state-of-the-art random forest benchmark, whereas our model achieves better interpretability and comparable training times. We examine how to improve performance in the near term, validating our ideas with tensor-networks-based numerical simulations.

Langevin dynamical simulations are performed to investigate the dislocation internal friction (IF) of solid two-dimensional (2D) dusty plasmas under oscillating shear deformations. The magnitude of IF is quantified using the loss factor $Q^{-1}$ from the stress-strain hysteresis. It is discovered that the dislocation IF is significantly dependent on the dislocation's slip direction relative to the shear direction. It is found that the variation trend of the dislocation IF with the dislocation's slip direction is positively related to the dislocation's slip distance, while the energy loss occurs due to the generation of shear bands. The dislocation IF in solid 2D dusty plasmas is found to be heavily dependent on the shear deformation frequency, while nearly independent of the shear strain amplitude, corresponding to a typical anelastic property.

We describe astra (attosecond transitions), a close-coupling approach to molecular ionization that uses many-body transition-density matrices between ionic states with arbitrary spin and symmetry, in combination with hybrid integrals between Gaussian and numerical orbitals, to efficiently evaluate photoionization observables. Within the transition-density-matrix approach, the evaluation of interchannel coupling is exact and does not depend on the size of the configuration-interaction space of the ions. Thanks to these two crucial features, astra opens the way to studying highly correlated and comparatively large targets at a manageable computational cost. Here, astra is used to predict the parameters of bound and autoionizing states of the boron atom and of the ${\mathrm{N}}_2$ molecule, as well as the total photoionization cross section of boron, the nitrogen molecule $\left({\mathrm{N}}_2\right)$, and formaldehyde $\left({\mathrm{H}}_2\mathrm{CO}\right)$. Our results are in excellent agreement with theoretical and experimental values from the literature.

B-rich metal compounds have garnered significant attention due to their diverse polymeric boron structures and versatile properties including high melting temperature, exceptional hardness, and superconductivity. In this paper, we systematically investigate the ternary phase diagram of the Li-Mn-B system at 0–100 GPa, employing a combination of crystal structure prediction methods and first-principles calculations. We identify five pressure-stabilized compounds with stoichiometries of ${\mathrm{Li}}_2\mathrm{Mn}{\mathrm{B}}_2, \mathrm{LiMn}{\mathrm{B}}_3, \mathrm{LiMn}{\mathrm{B}}_4, {\mathrm{Li}}_2\mathrm{Mn}{\mathrm{B}}_8$, and $\mathrm{LiMn}{\mathrm{B}}_{10}$. These pressure-induced compounds can be recovered to ambient pressure conditions. Notably, the boron atoms in these compounds exhibit diverse polymerization patterns, forming structures such as dimers, zigzag chains, ribbons, kagome lattices, and three-dimensional channel frameworks. The five Li-Mn-B compounds are potential hard materials, with $\mathrm{LiMn}{\mathrm{B}}_4$ standing out with a remarkable hardness value of 39.47 GPa. $\mathrm{LiMn}{\mathrm{B}}_4$ and $\mathrm{LiMn}{\mathrm{B}}_{10}$ are indirect semiconductors with band gaps of 0.92 and 0.64 eV, respectively. Notably, $\mathrm{LiMn}{\mathrm{B}}_{10}$ exhibits a lower effective mass than silicon, superior solar cell efficiency compared with silicon, and a work function comparable with that of silicon. These properties highlight the considerable potential of $\mathrm{LiMn}{\mathrm{B}}_{10}$ as a viable material for photovoltaic applications. ${\mathrm{Li}}_2\mathrm{Mn}{\mathrm{B}}_8$ is predicted to be a superconductor with a critical temperature of 15 K at 50 GPa. When the pressure is reduced to 0 GPa, ${\mathrm{Li}}_2\mathrm{Mn}{\mathrm{B}}_8$ displays antiferromagnetic properties. $\mathrm{LiMn}{\mathrm{B}}_3$ is a suitable precursor to obtain a ${\mathrm{B}}_{20}$-caged structure with remarkable superconductivity at ambient pressure, reaching a $T_{\mathrm{c}}$ of 31 K. In this paper, we provide comprehensive insights into the ternary phase diagram of the Li-Mn-B system at high pressure, elucidating the formation of various stable compounds with intriguing properties.

Rapid progress in developing near- and long-term quantum algorithms for quantum chemistry has provided us with an impetus to move beyond traditional approaches and explore new ways to apply quantum computing to electronic structure calculations. In this work, we identify the connection between quantum many-body theory and a quantum linear solver, and implement the Harrow-Hassidim-Lloyd (HHL) algorithm to make precise predictions of correlation energies for light molecular systems via the (nonunitary) linearized coupled cluster theory, where the term “light molecular systems” refers to those molecules whose constituent atoms have low atomic number. For the purposes of practical computations, we make suitable changes to the HHL framework. This entails two aspects: (1) Adapt, prescribing a novel scaling approach that allows one to scale any arbitrary Hermitian matrix, $A$, that in turn dictates the controlled-rotation angles without having to precompute the eigenvalues of $A$, and yet achieve a reasonably high precision in $|x\rangle$, and (2) Lite, for which we devise techniques that reduce the depth of the relevant quantum circuit. In this context, we introduce the following variants of HHL for different eras of quantum computing: AdaptHHLite in its appropriate forms for noisy intermediate-scale quantum (NISQ), late-NISQ, and the early fault-tolerant eras, as well as AdaptHHL for the fault-tolerant quantum computing era. We demonstrate the ability of the NISQ variant of AdaptHHLite to capture correlation energy precisely, while simultaneously being resource lean, using simulation as well as the 11-qubit IonQ quantum hardware.

Data-driven approaches that infer the local structures responsible for plasticity in amorphous materials have made substantial contributions to our understanding of the failure, flow, and rearrangement dynamics of supercooled fluids. Some of these methods, such as the “softness” approach, have identified combinations of local structural features in a supercooled particle's environment that predict energy barriers associated with particle rearrangements. This approach also predicts the onset temperature, often characterized as the temperature below which the system's dynamics becomes non-Arrhenius and above which local structures are no longer predictive of dynamical activity. We implement a transfer learning approach in which we first show that classifiers can be trained to predict dynamical activity even far above the onset temperature. We then show that applying these classifiers to data from the supercooled phase recovers the same essential physical information about the relationship between local structures and energy barriers that softness does.

Universal topological data of topologically ordered phases can be captured by topological quantum field theory in continuous space time by taking the limit of low energies and long wavelengths. While previous continuum field-theoretical studies of topological orders in three-dimensional (3D) real space focused on either self-statistics, braiding statistics, shrinking rules, fusion rules, or quantum dimensions, it has yet to systematically put all topological data together in a unified continuum field-theoretical framework. Here, we construct the topological $BF$ field theory with twisted terms (e.g., $AAdA$ and $AAB$) as well as a $K$-matrix $BB$ term to simultaneously explore all such topological data and reach anomaly-free topological orders. Following the spirit of the famous $K$-matrix Chern-Simons theory of two-dimensional topological orders, we present general formulas and systematically show how the $K$-matrix $BB$ term confines topological excitations, and how self-statistics of particles is transmuted between bosonic one and fermionic one. To reach anomaly-free topological orders, we explore, within the present continuum field-theoretical framework, how the principle of gauge invariance fundamentally influences possible realizations of topological data. More concretely, we present the topological actions of (i) particle-loop braidings with emergent fermions, (ii) multiloop braidings with emergent fermions, and (iii) Borromean rings braidings with emergent fermions, and calculate their universal topological data. Together with previous efforts, our paper paves the way toward a more systematic and complete continuum field-theoretical analysis of exotic topological properties of 3D topological orders. Several interesting future directions are also discussed.

The quest for a half-quantized thermal Hall effect of a Kitaev system represents an important tool to probe topological edge currents of emergent Majorana fermions. Pertinent experimental findings for $\alpha \text{−}{\mathrm{RuCl}}_3$ are, however, strongly debated, and it has been argued that the thermal Hall signal stems from phonons or magnons rather than from Majorana fermions. Here, we investigate the thermal Hall effect of the Kitaev candidate material ${\mathrm{Na}}_2{\mathrm{Co}}_2{\mathrm{TeO}}_6$, and we show that the measured signal emerges from at least two components, phonons and magnetic excitations. This dichotomy results from our discovery that the longitudinal and transversal heat conductivities share clear phononic signatures, while the transversal signal changes sign upon entering the low-temperature, magnetically ordered phase. Our results demonstrate that uncovering a genuinely quantized magnetic thermal Hall effect in Kitaev topological quantum spin liquids such as $\alpha \text{−}{\mathrm{RuCl}}_3$ and ${\mathrm{Na}}_2{\mathrm{Co}}_2{\mathrm{TeO}}_6$ requires disentangling phonon vs magnetic contributions, including potentially fractionalized excitations such as the expected Majorana fermions.

We show here using atomistic simulations that ${\mathrm{BiFeO}}_3$ films can be driven through a topological transition when increasing uniaxial anisotropy, which can possibly be achieved by strain. Tuning the anisotropy close to the transition, we show that individual antiferromagnetic skyrmions can reach a very large topological protection. These entities can then be excited by electric fields and spin torque and controllably driven at speeds exceeding 10 km/s.

Three-dimensional (3D) gapped topological phases with fractional excitations are divided into two subclasses: one has topological order with point-like and loop-like excitations fully mobile in the 3D space, and the other has fracton order with point-like excitations constrained in lower-dimensional subspaces. These exotic phases are often studied by exactly solvable Hamiltonians made of commuting projectors, which, however, are not capable of describing those exhibiting surface states with gapless chiral dispersion. Here we introduce a systematic way, based on cellular construction recently proposed for 3D topological phases, to construct another type of exactly solvable models in terms of coupled quantum wires with given inputs of cellular structure, two-dimensional Abelian topological order, and their gapped interfaces. We show that our models can describe both 3D topological and fracton orders (and even their hybrid) and study their universal properties such as quasiparticle statistics and topological ground-state degeneracy. We also apply this construction to two-dimensional coupled-wire models with ordinary topological orders and translation-symmetry-enriched topological orders. Our results pave the way for effective quantum field theory descriptions or microscopic model realizations of fracton orders with chiral gapless surface states.