Quantum sensing exploits the fundamental features of a quantum system to achieve highly efficient measurement of physical quantities. Here, we propose a strategy to realize a single-qubit pseudo-Hermitian sensor from a dilated two-qubit Hermitian system. The pseudo-Hermitian sensor exhibits divergent susceptibility in a dynamical evolution that does not necessarily involve an exceptional point. We demonstrate its potential advantages to overcome noises that cannot be averaged out by repetitive measurements. The proposal is feasible with the state-of-art experimental capability in a variety of qubit systems, and represents a step towards the application of non-Hermitian physics in quantum sensing.

A key strategy for sub-GeV dark matter direct detection is searches for small ionization signals that arise from dark matter-electron scattering or from the “Migdal” effect in dark matter-nucleus scattering. We show that the theoretical description of both processes is closely related, allowing for a principal mapping between them. We explore this for noble-liquid targets and, for the first time, estimate the Migdal effect in semiconductors using a crystal form factor. We present new constraints using XENON10, XENON100, and SENSEI data, and give projections for proposed experiments.

Spectroscopic factors of neutron-hole and proton-hole states in ${}^{131}\mathrm{Sn}$ and ${}^{131}\mathrm{In}$, respectively, were measured using one-nucleon removal reactions from doubly magic ${}^{132}\mathrm{Sn}$ at relativistic energies. For ${}^{131}\mathrm{In}$, a 2910(50)-keV $\gamma$ ray was observed for the first time and tentatively assigned to a decay from a ${5/2}^{-}$ state at 3275(50) keV to the known ${1/2}^{-}$ level at 365 keV. The spectroscopic factors determined for this new excited state and three other single-hole states provide first evidence for a strong fragmentation of single-hole strength in ${}^{131}\mathrm{Sn}$ and ${}^{131}\mathrm{In}$. The experimental results are compared to theoretical calculations based on the relativistic particle-vibration coupling model and to experimental information for single-hole states in the stable doubly magic nucleus ${}^{208}\mathrm{Pb}$.

Recent optomechanical experiments have observed nonclassical properties in macroscopic mechanical oscillators. A key indicator of such properties is the asymmetry in the strength of the motional sidebands produced in the probe electromagnetic field, which is originated by the noncommutativity between the oscillator ladder operators. Here we extend the analysis to a squeezed state of an oscillator embedded in an optical cavity, produced by the parametric effect originated by a suitable combination of optical fields. The motional sidebands assume a peculiar shape, related to the modified system dynamics, with asymmetric features revealing and quantifying the quantum component of the squeezed oscillator motion.

The picosecond evolution of non-Maxwellian electron distribution functions was measured in a laser-produced plasma using collective electron plasma wave Thomson scattering. During the laser heating, the distribution was measured to be approximately super-Gaussian due to inverse bremsstrahlung heating. After the heating laser turned off, collisional ionization caused further modification to the distribution function while increasing electron density and decreasing temperature. Electron distribution functions were determined using Vlasov-Fokker-Planck simulations including atomic kinetics.

It is known that both magnetic and nonmagnetic impurities suppress unconventional superconductivity. Here we compare their effect on the paradigm unconventional superconductor, superfluid ${}^3\mathrm{He}$, using highly dilute silica aerogel. Switching magnetic to nonmagnetic scattering in the same physical system is achieved by coating the aerogel surface with ${}^4\mathrm{He}$. We find a marginal influence on the transition temperature itself. However, we have discovered that the $A$ phase, which breaks time reversal symmetry, is strongly influenced, while the isotropic $B$ phase is unchanged. Importantly, this occurs only if the impurities are anisotropically distributed on a global scale.

We introduce a novel method for the simulation of the impact scattering in vibrational scanning transmission electron microscopy electron energy loss spectroscopy simulations. The phonon-loss process is modeled by a combination of molecular dynamics and elastic multislice calculations within a modified frozen phonon approximation. The key idea is thereby to use a so-called $\delta$ thermostat in the classical molecular dynamics simulation to generate frequency dependent configurations of the vibrating specimen’s atomic structure. The method includes correlated motion of atoms and provides vibrational spectrum images at a cost comparable to standard frozen phonon calculations. We demonstrate good agreement of our method with simulations and experiments for a 15 nm flake of hexagonal boron nitride.

Artificial crystals synthesized by atomic-scale epitaxy provide the ability to control the dimensions of the quantum phases and associated phase transitions via precise thickness modulation. In particular, the reduction in dimensionality via quantized control of atomic layers is a powerful approach to revealing hidden electronic and magnetic phases. Here, we demonstrate a dimensionality-controlled and induced metal-insulator transition (MIT) in atomically designed superlattices by synthesizing a genuine two-dimensional (2D) ${\mathrm{SrRuO}}_3$ crystal with highly suppressed charge transfer. The tendency to ferromagnetically align the spins in an ${\mathrm{SrRuO}}_3$ layer diminishes in 2D as the interlayer exchange interaction vanishes, accompanying the 2D localization of electrons. Furthermore, electronic and magnetic instabilities in the two ${\mathrm{SrRuO}}_3$ unit cell layers induce a thermally driven MIT along with a metamagnetic transition.

Using the semiclassical quantum Boltzmann equation (QBE), we numerically calculate the dc transport properties of bilayer graphene near charge neutrality. We find, in contrast to prior discussions, that phonon scattering is crucial even at temperatures below 40 K. Nonetheless, electron-electron scattering still dominates over phonon collisions allowing a hydrodynamic approach. We introduce a simple two-fluid hydrodynamic model of electrons and holes interacting via Coulomb drag and compare our results to the full QBE calculation. We show that the two-fluid model produces quantitatively accurate results for conductivity, thermopower, and thermal conductivity.

We demonstrate nondecaying, steplike electrical switching of tristate Néel order in $\mathrm{Pt}/\alpha \text{−}{\mathrm{Fe}}_2{\mathrm{O}}_3$ bilayers detected by the spin-Hall induced anomalous Hall effect. The as-grown $\mathrm{Pt}/\alpha \text{−}{\mathrm{Fe}}_2{\mathrm{O}}_3$ bilayers exhibit sawtooth switching behavior generated by current pulses. After annealing by a high pulse current, the Hall signals reveal single-pulse saturated, nondecaying, steplike switching. Together with control experiments, we show that the sawtooth switching is due to an artifact of Pt while the actual spin-orbit torque induced antiferromagnetic switching is steplike. Our Monte Carlo simulations explain the switching behavior of $\alpha \text{−}{\mathrm{Fe}}_2{\mathrm{O}}_3$ Néel order among three in-plane easy axes.

Molecular dynamics simulations confirm recent extensional flow experiments showing ring polymer melts exhibit strong extension-rate thickening of the viscosity at Weissenberg numbers $\mathrm{Wi}\ll 1$. Thickening coincides with the extreme elongation of a minority population of rings that grows with Wi. The large susceptibility of some rings to extend is due to a flow-driven formation of topological links that connect multiple rings into supramolecular chains. Links form spontaneously with a longer delay at lower Wi and are pulled tight and stabilized by the flow. Once linked, these composite objects experience larger drag forces than individual rings, driving their strong elongation. The fraction of linked rings depends nonmonotonically on Wi, increasing to a maximum when $\mathrm{Wi}\sim 1$ before rapidly decreasing when the strain rate approaches $1/{\tau }_e$.

The attractive tail of the intermolecular interaction affects very weakly the structural properties of liquids, while it affects dramatically their dynamical ones. Via the numerical simulations of model systems not prone to crystallization, both in three and in two spatial dimensions, here we demonstrate that the nonperturbative dynamical effects of the attractive forces are tantamount to a rescaling of the activation energy by the glass transition temperature $T_g$: systems only differing in their attractive interaction have the same structural and dynamical properties if compared at the same value of $T/T_g$.

Cells estimate concentrations of chemical ligands in their environment using a limited set of receptors. Recent work has shown that the temporal sequence of binding and unbinding events on just a single receptor can be used to estimate the concentrations of multiple ligands. Here, for a network of many ligands and many receptors, we show that such temporal sequences can be used to estimate the concentration of a few times as many ligand species as there are receptors. Crucially, we show that the spectrum of the inverse covariance matrix of these estimates has several universal properties, which we trace to properties of Vandermonde matrices. We argue that this can be used by cells in realistic biochemical decoding networks.

We consider a three-layer Sejnowski machine and show that features learnt via contrastive divergence have a dual representation as patterns in a dense associative memory of order $P=4$. The latter is known to be able to Hebbian store an amount of patterns scaling as $N^{P-1}$, where $N$ denotes the number of constituting binary neurons interacting $P$ wisely. We also prove that, by keeping the dense associative network far from the saturation regime (namely, allowing for a number of patterns scaling only linearly with $N$, while $P>2$) such a system is able to perform pattern recognition far below the standard signal-to-noise threshold. In particular, a network with $P=4$ is able to retrieve information whose intensity is $\mathcal{O}(1)$ even in the presence of a noise $\mathcal{O}(\sqrt{N})$ in the large $N$ limit. This striking skill stems from a redundancy representation of patterns—which is afforded given the (relatively) low-load information storage—and it contributes to explain the impressive abilities in pattern recognition exhibited by new-generation neural networks. The whole theory is developed rigorously, at the replica symmetric level of approximation, and corroborated by signal-to-noise analysis and Monte Carlo simulations.

One-dimensional polar gases in deep optical lattices present a severely constrained dynamics due to the interplay between dipolar interactions, energy conservation, and finite bandwidth. The appearance of dynamically bound nearest-neighbor dimers enhances the role of the $1/r^3$ dipolar tail, resulting in the absence of external disorder, in quasi-localization via dimer clustering for very low densities and moderate dipole strengths. Furthermore, even weak dipoles allow for the formation of self-bound superfluid lattice droplets with a finite doping of mobile, but confined, holons. Our results, which can be extrapolated to other power-law interactions, are directly relevant for current and future lattice experiments with magnetic atoms and polar molecules.

Single-qubit measurements are typically insufficient for inferring arbitrary quantum states of a multiqubit system. We show that, if the system can be fully controlled by driving a single qubit, then utilizing a local random pulse is almost always sufficient for complete quantum-state tomography. Experimental demonstrations of this principle are presented using a nitrogen-vacancy (NV) center in diamond coupled to a nuclear spin, which is not directly accessible. We report the reconstruction of a highly entangled state between the electron and nuclear spin with fidelity above 95% by randomly driving and measuring the NV-center electron spin only. Beyond quantum-state tomography, we outline how this principle can be leveraged to characterize and control quantum processes in cases where the system model is not known.

We report the direct characterization of energy-time entanglement of narrow-band biphotons produced from spontaneous four-wave mixing in cold atoms. The Stokes and anti-Stokes two-photon temporal correlation is measured by single-photon counters with nanosecond temporal resolution, and their joint spectrum is determined by using a narrow linewidth optical cavity. The energy-time entanglement is verified by the joint frequency-time uncertainty product of $0.063\pm 0.0044$, which does not only violate the separability criterion but also satisfies the continuous variable Einstein-Podolsky-Rosen steering inequality.

Entanglement between stationary quantum memories and photonic channels is the essential resource for future quantum networks. Together with entanglement distillation, it will enable efficient distribution of quantum states. We report on the generation and observation of entanglement between a ${}^{87}\mathrm{Rb}$ atom and a photon at telecom wavelength transmitted through up to 20 km of optical fiber. For this purpose, we use polarization-preserving quantum frequency conversion to transform the wavelength of a photon entangled with the atomic spin state from 780 nm to the telecom $S$ band at 1522 nm. We achieve an unprecedented external device conversion efficiency of 57% and observe an entanglement fidelity between the atom and telecom photon of $\ge 78.5\pm 0.9\%$ after transmission through 20 km of optical fiber, mainly limited by decoherence of the atomic state. This result is an important milestone on the road to distribute quantum information on a large scale.