Sandstorms are frequently accompanied by intense electric fields and lightning. In a very narrow region close to the ground, sand particles undergo a charge exchange during which larger-sized sand grains become positively charged and smaller-sized sand grains become negatively charged, and then all particles become suspended by the turbulent fluid motion. Although the association of intense electric fields with sandstorms has long been observed, the mechanism that causes these intense electric fields has not yet been described. Here, we hypothesize that differently sized sand particles are differentially transported by turbulence in the flow, resulting in a large-scale charge separation and a consequential large-scale electric field. To confirm our hypothesis, we combined a large-eddy simulation framework comprising a turbulent atmospheric boundary layer and movement of sand particles with an electrostatic Gauss law to investigate the physics of the electric fields in sandstorms. We varied the strength of the sandstorm from weak to strong as parametrized by the number density of the entrained sand particles. Our simulations reproduced observational measurements of both mean and root mean squared fluctuation values of the electric field. Our results allowed us to propose a law in which the electric field scales to two-thirds of the power of the concentration of the sand particles in weak to medium strength sandstorms.

We perform systematic high-resolution angle-resolved photoemission spectroscopy of iron-chalcogenide superconductor ${\mathrm{FeSe}}_{1-x}{\mathrm{Te}}_x$ films on ${\mathrm{CaF}}_2$ which exhibit a unique paramagnetic nematicity at $x=0$ (pristine FeSe) and a gigantic $T_{\mathrm{c}}$ enhancement at the critical Te concentration ($x_{\mathrm{c}}$) of $x\sim 0.2$. Upon increasing the Te concentration from $x=0$, the electronlike Fermi-surface shape at the Brillouin-zone corner shows a clear change associated with a remarkable energy shift of the $d_{xz/yz}$ orbital, indicative of the suppression of nematicity near $x_{\mathrm{c}}$. Evolution of band structure at the Brillouin-zone center is characterized by a drastic upward shift of the $d_{xy}$ band with increasing $x$, leading to an orbital switching from $d_{xz/yz}$ to $d_{xz/yz}+d_{xy}$ accompanied by a mass enhancement. These results demonstrate that the pristine and high-$T_{\mathrm{c}}{\mathrm{FeSe}}_{1-x}{\mathrm{Te}}_x$ have distinctly different electronic structures. The present study lays the foundation for understanding the origin of high-$T_{\mathrm{c}}$ superconductivity and the interplay with electronic nematicity.

Near-term quantum computers are noisy, and therefore must run algorithms with a low circuit depth and qubit count. Here we investigate how noise affects a quantum neural network (QNN) for state discrimination, which is applicable on near-term quantum devices as it fulfils the above criteria. We find that for the required gradient calculation on a noisy device a quantum circuit with a large number of parameters is disadvantageous. By introducing a smaller circuit ansatz we overcome this limitation, and find that the QNN performs well at noise levels of current quantum hardware. We present a model showing that the main effect of the noise is to increase the overlap between the states as circuit gates are applied, hence making discrimination more difficult. Our findings demonstrate that noisy quantum computers can be used for state discrimination and other applications, such as classifiers of the output of quantum generative adversarial networks.

We characterize the Casimir forces for the Dirac vacuum on free-fermionic chains with smoothly varying hopping amplitudes, which correspond to ($1+1$)-dimensional [($1+1$)D] curved spacetimes with a static metric in the continuum limit. The first-order energy potential for an obstacle on that lattice corresponds to the Newtonian potential associated with the metric, while the finite-size corrections are described by a curved extension of the conformal field theory predictions, including a suitable boundary term. We show that for weak deformations of the Minkowski metric, Casimir forces measured by a local observer at the boundary are universal. We provide numerical evidence for our results on a variety of ($1+1$)D deformations: Minkowski, Rindler, anti–de Sitter (the so-called rainbow system), and sinusoidal metrics. Moreover, we show that interactions do not preclude our conclusions, exemplifying this with the deformed Heisenberg chain.

The planar Hall effect (PHE) is the appearance of an in-plane transverse voltage in the presence of coplanar electric and magnetic fields. Its hallmark is a characteristic $\pi$ periodic, i.e., even under a magnetic-field reversal, angular dependence with the transverse voltage that exactly vanishes when the electric and magnetic fields are aligned. Here we demonstrate that in two-dimensional trigonal crystals Zeeman-induced nontrivial Berry curvature effects yield a previously unknown anomalous PHE that is odd in the magnetic field and independent of the relative angle with the driving electric field. We further show that when an additional mirror symmetry forces the transverse voltage to vanish in the linear-response regime, the anomalous PHE can occur as a second-order response at both zero and twice the frequency of the applied electric field. We demonstrate that this nonlinear PHE possesses an antisymmetric quantum contribution that originates from a Zeeman-induced Berry curvature dipole.

We discuss the properties of the distributions of energies of minima obtained by gradient descent in complex energy landscapes. We find strikingly similar phenomenology across several prototypical models. We particularly focus on the distribution of energies of minima in the analytically well-understood $p$-spin-interaction spin-glass model. We numerically find non-Gaussian distributions that resemble the Tracy-Widom distributions often found in problems of random correlated variables, and nontrivial finite-size scaling. Based on this, we propose a picture of gradient-descent dynamics that highlights the importance of a first-passage process in the eigenvalues of the Hessian. This picture provides a concrete link to problems in which the Tracy-Widom distribution is established. Aspects of this first-passage view of gradient-descent dynamics are generic for nonconvex complex landscapes, rationalizing the commonality that we find across models.

The discrete truncated Wigner approximation (DTWA) is a powerful tool for analyzing dynamics of quantum spin systems. Since the DTWA includes the leading-order quantum corrections to a mean-field approximation, it is naturally expected that the DTWA becomes more accurate when the range of interactions of the system increases. However, quantitative corroboration of this expectation is still lacking mainly because it is generally difficult in a large system to evaluate a timescale on which the DTWA is quantitatively valid. In order to investigate how the validity timescale depends on the interaction range, we analyze dynamics of quantum spin models with a step function type interaction subjected to a sudden quench of a magnetic field by means of both DTWA and its extension including the second-order correction, which is derived from the Bogoliubov-Born-Green-Kirkwood-Yvon equation. We also develop a formulation for calculating the second-order Rényi entropy within the framework of the DTWA. By comparing the time evolution of the Rényi entropy computed by the DTWA with that by the extension including the correction, we find that both in the one- and two-dimensional systems the validity timescale increases algebraically with the range of the step function type interaction.

We examine the magnetic susceptibility of topological insulators microscopically and find that the orbital-Zeeman (OZ) cross term, the cross term between the orbital effect and the spin Zeeman effect, is directly related to the Berry curvature when the $z$ component of spin is conserved. In particular, the OZ cross term reflects the spin Chern number, which results in the quantization of the magnetic susceptibility jump at the topological phase transition. The magnitude of the jump is in units of the universal value $4\left|e\right|{\mu }_B/h$. We also apply the obtained formula to an explicit model and demonstrate the quantization. For this model, the physical origin of this quantization is clarified.

Citizen science methodologies have over the past decade been applied with great success to help solve highly complex numerical challenges. Here, we take early steps in the quantum physics arena by introducing a citizen science game, Quantum Moves 2, and compare the performance of different optimization methods across three different quantum optimal control problems of varying difficulty. Inside the game, players can apply a gradient-based algorithm (running locally on their device) to optimize their solutions and we find that these results perform roughly on par with the best of the tested standard optimization methods performed on a computer cluster. In addition, cluster-optimized player seeds was the only method to exhibit roughly optimal performance across all three challenges. Finally, player seeds show significant statistical advantages over random seeds in the limit of sparse sampling. This highlights the potential for crowdsourcing the solution of future quantum research problems.

We build exactly solvable lattice Hamiltonians for fermionic symmetry-protected topological (SPT) phases in ($3+1$)D classified by group supercohomology. A central benefit of our construction is that it produces an explicit finite-depth quantum circuit (FDQC) that prepares the ground state from an unentangled symmetric state. The FDQC allows us to clearly demonstrate the characteristic properties of supercohomology phases—namely, symmetry fractionalization on fermion parity flux loops—predicted by continuum formulations. By composing the corresponding FDQCs, we also recover the stacking relations of supercohomology phases. Furthermore, we derive topologically ordered gapped boundaries for the supercohomology models by extending the protecting symmetries, analogous to the construction of topologically ordered boundaries for bosonic SPT phases. Our approach relies heavily on dualities that relate certain bosonic 2-group SPT phases with supercohomology SPT phases. We develop physical motivation for the dualities in terms of explicit lattice prescriptions for gauging a 1-form symmetry and for condensing emergent fermions. We also comment on generalizations to supercohomology phases in higher dimensions and to fermionic SPT phases outside of the supercohomology framework.

Several processes in the cell, such as gene regulation, start when key proteins recognize and bind to short DNA sequences. However, as these sequences can be hundreds of million times shorter than the genome, they are hard to find by simple diffusion: diffusion-limited association rates may underestimate in vitro measurements up to several orders of magnitude. Moreover, the rates increase if the DNA is coiled rather than straight. Here we model how this works in vivo in mammalian cells. We use chromatin-chromatin contact data from Hi-C experiments to map the protein target-search onto a network problem. The nodes represent DNA segments and the weight of the links are proportional to measured contact probabilities. We then put forward a diffusion-reaction equation for the density of searching protein that allows us to calculate the association rates across the genome analytically. For segments where the rates are high, we find that they are enriched with active gene starts and have high RNA expression levels. This paper suggests that the DNA's 3D conformation is important for protein search times in vivo and offers a method to interpret protein-binding profiles in eukaryotes that cannot be explained by the DNA sequence itself.

Scattering phase shift, as a key parameter in scattering theory, plays an important role in characterizing low-energy collisions between ultracold atoms. In this work, we theoretically investigate the universal low-energy behavior of the scattering phase shifts for cold atoms in the presence of spin-orbit coupling. We first construct the asymptotic form of the two-body wave function when two fermions get as close as the interaction range, and consider perturbatively the correction of the spin-orbit coupling up to the second order, in which new scattering parameters are introduced. Then, for elastic collisions, the scattering phase shifts are defined according to the unitary scattering $S$ matrix. We show how the low-energy behavior of the scattering phase shifts is modified by these new scattering parameters introduced by spin-orbit coupling. The universality of the scattering phase shifts is manifested as the independence of the specific form of the interatomic potential. The explicit forms of the new scattering parameters are analytically derived within a model of the spherical-square-well potential. Our method provides a unified description of the low-energy properties of scattering phase shifts in the presence of spin-orbit coupling.

Densest-packed structures of identical ellipses within a parallel strip have been obtained through Monte Carlo simulations and analytic derivations. Each of such structures is an affine transformation of a particular densest-packed structure of identical circular disks. Three types of structures have been identified: Types $\mathcal{X}$ and $\mathcal{Y}$ correspond, respectively, to affine stretches along the perpendicular and axial directions of the parallel strip, and type $\mathcal{M}$ corresponds to affine stretches of locally densest structures. Our findings enrich the field of condensed matter physics with a class of confinement-induced, orientationally ordered crystal structures, and offer possibilities of developing low-dimensional materials with specific orientational ordering.

Skyrmions have attracted rapidly growing interest due to their topological properties and unique aspects for potential novel applications such as data storage and soft robotics. They can also serve as key elements for materials by design, self-assembly, and functional soft materials. While not real particles, these skyrmions behave like particles—they interact with each other and can be actuated by means of electric field, surface anchoring, and light. On the other hand, they are field configurations which have properties not possessed by real particles. Here we show that, by means of alignment-induced attractive and repulsive walls, skyrmions in chiral nematic liquid crystals can be precisely controlled and programed to serve as suitable building blocks for the realization of the above goals. Our work may stimulate new experimental efforts and concomitant applications in this direction.

The celebrated tenfold way of Altland-Zirnbauer symmetry classes discern any quantum system by its pattern of nonspatial symmetries. It lays at the core of the periodic table of topological insulators and superconductors which provided a complete classification of weakly interacting electrons' noncrystalline topological phases for all symmetry classes. Over recent years, a plethora of topological phenomena with diverse surface states has been discovered in crystalline materials. In this paper, we obtain an exhaustive classification of topologically distinct ground states as well as topological phases with anomalous surface states of crystalline topological insulators and superconductors for key space-groups, layer-groups, and rod-groups. This is done in a unified manner for the full tenfold way of Altland-Zirnbauer nonspatial symmetry classes. We establish a comprehensive paradigm that harnesses the modern mathematical framework of equivariant spectra; it allows us to obtain results applicable to generic topological classification problems. In particular, this paradigm provides efficient computational tools that enable an inherently unified treatment of the full tenfold way.

We discuss transport properties of fully spin-polarized triplet superconductors, where only electrons of one spin component (along a certain axis) are paired. Due to the structure of the order parameter space, wherein phase and spin rotations are intertwined, a configuration where the superconducting phase winds by $4\pi$ in space is topologically equivalent to a configuration with no phase winding. This opens the possibility of supercurrent relaxation by a smooth deformation of the order parameter, where the order parameter remains nonzero at any point in space throughout the entire process. During the process, a spin texture is formed. We discuss the conditions for such processes to occur and their physical consequences. In particular, we show that when a voltage is applied, they lead to an unusual alternating-current Josephson effect whose period is an integer multiple of the usual Josephson period. These conclusions are substantiated in a simple time-dependent Ginzburg-Landau model for the dynamics of the order parameter. One of the potential applications of our analysis is for moiré systems, such as twisted bilayer and double bilayer graphene, where superconductivity is found in the vicinity of ferromagnetism.

We propose to use frequency-selective dissipative coupling to reduce the heat generated by coherent anti-Stokes Raman scattering (CARS) reversed cycles in active Raman media with phase mismatch. This is accomplished using a coupled-waveguide structure, which includes the active Raman waveguide (RW), where the Stokes signal undergoes amplification via stimulated Stokes Raman scattering (SSRS), and a dissipative waveguide (DW), which is tuned to the anti-Stokes wavelength so as to evacuate the corresponding anti-Stokes photons from the RW by coupling. The DW introduces optical loss that partially offsets the growth of the anti-Stokes signal in the RW and hence suppress the reversed CARS cycles that would otherwise result into heat generation in the RW. It is shown that the frequency-selective dissipative coupling provided by the DW can reduce the heat in active Raman media by a very factor of up to 5 when the CARS phase mismatch is compensated for by the optimum level of coupling between the RW and the DW.

Composite particles—atoms, molecules, or microspheres—are unique tools for testing joint quantum and general relativistic effects, macroscopic limits of quantum mechanics, and searching for new physics. However, all studies of the free propagation of these particles find that they delocalize into separate internal energy components, destroying their spatial coherence. This renders them unsuitable for experimental applications, as well as theoretical studies where they are used as idealized test masses or clocks. Here we solve this problem by introducing a class of states with minimal uncertainty in spacetime that fully overcome the delocalization. The relevant physics comes from minimizing the uncertainty between position and velocity, rather than position and momentum, while directly accounting for mass as an operator. Our results clarify the nature of composite particles, providing a currently missing theoretical tool with direct relevance for studies of joint foundations of quantum and relativistic phenomena, which removes a roadblock that could limit near-future quantum tests using composite particles.

Shock waves launched by x-ray pulses in sample-carrying liquid jets may affect protein crystallography data collected at MHz repetition rate x-ray free-electron laser (XFEL) facilities, by damaging the crystals before they are probed. We investigated the shock damage in lysozyme microcrystals using a double-pulse operation mode at a low repetition rate x-ray laser facility. The double-pulse mode generated shock waves with pressures that covered and exceeded the shock pressures expected at MHz pulse rate experiments at the European XFEL (EuXFEL) x-ray laser. The quality of the x-ray diffraction data from the crystals was degraded after the shock passed. A decrease in the number of peaks and in the resolution occurred above an estimated shock pressure threshold on the order of tens of MPa. Based on the scaling of the shock pressure with the sample injection parameters and the pulse rates, this threshold was not reached in initial EuXFEL experiments performed at pulse rates of 1.1 MHz but may be exceeded at the maximum pulse rate of 4.5 MHz. The observation of shock damage in lysozyme crystals indicates how experiments can be designed to rapidly detect, and eventually avoid, shock damage in other crystals. Our analysis of shock pressures in liquid jets can also be used to estimate the effect of the shocks in other types of experiments at MHz repetition rate XFELs.

Nonmagnetic impurities can lift the accidental degeneracy of unconventional pairing states, such as the $(d+ig)$-wave state recently proposed for ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$. This type of effect would lead to a superconducting double transition upon impurity doping. In a model calculation it is shown how this behavior depends on material parameters and how it could be detected.