We have examined the intrinsic spin-orbit coupling and orbital depairing in thin films of Nb-doped ${\mathrm{SrTiO}}_3$ by superconducting tunneling spectroscopy. The orbital depairing is geometrically suppressed in the two-dimensional limit, enabling a quantitative evaluation of the Fermi level spin-orbit scattering using Maki’s theory. The response of the superconducting gap under in-plane magnetic fields demonstrates short spin-orbit scattering times ${\tau }_{\mathrm{so}}\le 1.1\mathrm{ps}$. Analysis of the orbital depairing indicates that the heavy electron band contributes significantly to pairing. These results suggest that the intrinsic spin-orbit scattering time in ${\mathrm{SrTiO}}_3$ is comparable to those associated with Rashba effects in ${\mathrm{SrTiO}}_3$ interfacial conducting layers and can be considered significant in all forms of superconductivity in ${\mathrm{SrTiO}}_3$.

A magnetic order can be completely suppressed at zero temperature ($T$), by doping carriers or applying pressure, at a quantum critical point, around which physical properties change drastically. However, the situation is unclear for an electronic nematic order that breaks rotation symmetry. Here, we report nuclear magnetic resonance studies on ${\mathrm{NaFe}}_{1-x}{\mathrm{Co}}_x\mathrm{As}$ where magnetic and nematic transitions are well separated. The nuclear magnetic resonance spectrum is sensitive to inhomogeneous magnetic fields in the vortex state, which is related to London penetration depth ${\lambda }_L$ that measures the electron mass $m^{*}$. We discovered two peaks in the doping dependence of ${\lambda }_L^2(T\sim 0)$, one at $x_M=0.027$ where the spin-lattice relaxation rate shows quantum critical behavior, and another at $x_c=0.032$ around which the nematic transition temperature extrapolates to zero and the electrical resistivity shows a $T$-linear variation. Our results indicate that a nematic quantum critical point lies beneath the superconducting dome at $x_c$ where $m^{*}$ is enhanced. The impact of the nematic fluctuations on superconductivity is discussed.

Artificial neural networks have been recently introduced as a general ansatz to represent many-body wave functions. In conjunction with variational Monte Carlo calculations, this ansatz has been applied to find Hamiltonian ground states and their energies. Here, we provide extensions of this method to study excited states, a central task in several many-body quantum calculations. First, we give a prescription that allows us to target eigenstates of a (nonlocal) symmetry of the Hamiltonian. Second, we give an algorithm to compute low-lying excited states without symmetries. We demonstrate our approach with both restricted Boltzmann machines and feed-forward neural networks. Results are shown for the one-dimensional spin-$1/2$ Heisenberg model, and for the one-dimensional Bose-Hubbard model. When comparing to exact results, we obtain good agreement for a large range of excited-states energies. Interestingly, we find that deep networks typically outperform shallow architectures for high-energy states.

The interaction effects in ultracold Fermi gases with $\mathrm{SU}(N)$ symmetry are studied nonperturbatively in half filled one-dimensional lattices by employing quantum Monte Carlo simulations. We find that, as $N$ increases, weak and strong interacting systems are driven to a crossover region, but from opposite directions as a convergence of itinerancy and Mottness. In the weak interaction region, particles are nearly itinerant, and interparticle collisions are enhanced by $N$, resulting in the amplification of interaction effects. In contrast, in the strong coupling region, increasing $N$ softens the Mott-insulating background through the enhanced virtual hopping processes. The crossover region exhibits nearly $N$-independent physical quantities, including the relative bandwidth, Fermi distribution, and the spin structure factor. The difference between even-$N$ and odd-$N$ systems is most prominent at small $N$’s with strong interactions, since the odd case allows local real hopping with an energy scale much larger than the virtual one. The above effects can be experimentally tested in ultracold atom experiments with alkaline-earth(-like) fermions such as ${}^{87}\mathrm{Sr}$ (${}^{173}\mathrm{Yb}$).

Hydrogels made from structured polyprotein domains combine the properties of cross-linked polymers with the unfolding phase transition. The use of protein hydrogels as an ensemble approach to study the physics of domain unfolding is limited by the lack of scaling tools and by the complexity of the system. Here we propose a model to describe the biomechanical response of protein hydrogels based on the unfolding and extension of protein domains under force. Our model considers the contributions of the network dynamics of the molecules inside the gels, which have random cross-linking points and random topology. This model reproduces reported macroscopic viscoelastic effects and constitutes an important step toward using rheometry on protein hydrogels to scale down to the average mechanical response of protein molecules.

We develop a deterministic method to generate and verify arbitrarily high NOON states of quantized vibrations (phonons), through the coupling to the internal state. We experimentally create the entangled states up to $N=9$ phonons in two vibrational modes of a single trapped ${{}^{171}\mathrm{Yb}}^{+}$ ion. We observe an increasing phase sensitivity of the generated NOON state as the number of phonons $N$ increases and obtain the fidelity from the contrast of the phase interference and the population of the phonon states through the two-mode projective measurement, which are significantly above the classical bound. We also measure the quantum Fisher information of the generated state and observe Heisenberg scaling in the lower bounds of phase sensitivity as $N$ increases. Our scheme is generic and applicable to other photonic or phononic systems such as circuit QED systems or nanomechanical oscillators, which have Jaynes-Cummings-type of interactions.

Topological photonics has emerged recently as a smart approach for realizing robust optical circuitry, and the study of nonlinear effects is expected to open the door for tunability of photonic topological states. Here we realize experimentally nonlinearity-induced spectral tuning of electromagnetic topological edge states in arrays of coupled nonlinear resonators in the pump-probe regime. When nonlinearity is weak, we observe that the frequencies of the resonators exhibit spectral shifts concentrated mainly at the edge mode and affecting only weakly the bulk modes. For a strong pumping, we describe several scenarios of the transformation of the edge states and their hybridization with bulk modes, and also predict a parametrically driven transition from topological stationary to unstable dynamic regimes.

We present a detailed study of the temperature ($T$) and magnetic field ($H$) dependence of the electronic density of states (DOS) at the Fermi level, as deduced from specific heat and Knight shift measurements in underdoped ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_y$. We find that the DOS becomes field independent above a characteristic field $H_{\mathrm{DOS}}$, and that the $H_{\mathrm{DOS}}(T)$ line displays an unusual inflection near the onset of the long-range 3D charge-density wave order. The unusual $S$ shape of $H_{\mathrm{DOS}}(T)$ is suggestive of two mutually exclusive orders that eventually establish a form of cooperation in order to coexist at low $T$. On theoretical grounds, such a collaboration could result from the stabilization of a pair-density wave state, which calls for further investigation in this region of the phase diagram.

In this Letter, we show the demonstration of a sequential antiferromagnetic memory operation with a spin-orbit-torque write, by the spin Hall effect, and a resistive read in the CoGd synthetic antiferromagnetic bits, in which we reveal the distinct differences in the spin-orbit-torque and field-induced switching mechanisms of the antiferromagnetic moment, or the Néel vector. In addition to the comprehensive spin torque memory operation, our thorough investigations also highlight the high immunity to a field disturbance as well as a memristive behavior of the antiferromagnetic bits.

The $1/8$ fractional plateau phase ($1/8$ FPP) in Shastry-Sutherland lattice (SSL) spin systems has been viewed an exemplar of emergence on an Archimedean lattice. Here we explore this phase in the Ising magnet ${\mathrm{TmB}}_4$ using high-resolution specific heat ($C$) and magnetization ($M$) in the field-temperature plane. We show that the $1/8$ FPP is smoothly connected to the antiferromagnetic phase on ramping the field from $H=0$. Thus, the $1/8$ FPP is not a distinct thermodynamic ground state of ${\mathrm{TmB}}_4$. The implication of these results for Heisenberg spins on the SSL is discussed.

Quantum Darwinism posits that information becomes objective whenever multiple observers indirectly probe a quantum system by each measuring a fraction of the environment. It was recently shown that objectivity of observables emerges generically from the mathematical structure of quantum mechanics, whenever the system of interest has finite dimensions and the number of environment fragments is large [F. G. S. L. Brandão, M. Piani, and P. Horodecki, Nat. Commun. 6, 7908 (2015)]. Despite the importance of this result, it necessarily excludes many practical systems of interest that are infinite dimensional, including harmonic oscillators. Extending the study of quantum Darwinism to infinite dimensions is a nontrivial task: we tackle it here by using a modified diamond norm, suitable to quantify the distinguishability of channels in infinite dimensions. We prove two theorems that bound the emergence of objectivity, first for finite mean energy systems, and then for systems that can only be prepared in states with an exponential energy cutoff. We show that the latter class includes any bounded-energy subset of single-mode Gaussian states.

The quantum capacity of a quantum channel captures its capability for noiseless quantum communication. It lies at the heart of quantum information theory. Unfortunately, our poor understanding of nonadditivity of coherent information makes it hard to understand the quantum capacity of all but very special channels. In this Letter, we consider the dephrasure channel, which is the concatenation of a dephasing channel and an erasure channel. This very simple channel displays remarkably rich and exotic properties: we find nonadditivity of coherent information at the two-letter level, a substantial gap between the threshold for zero quantum capacity and zero single-letter coherent information, a big gap between single-letter coherent and private information, and positive quantum capacity for all complementary channels. Its clean form simplifies the evaluation of coherent information substantially and, as such, we hope that the dephrasure channel will provide a much-needed laboratory for the testing of new ideas about nonadditivity.

We show that hydrodynamic diffusion is generically present in many-body, one-dimensional interacting quantum and classical integrable models. We extend the recently developed generalized hydrodynamic (GHD) to include terms of Navier-Stokes type, which leads to positive entropy production and diffusive relaxation mechanisms. These terms provide the subleading diffusive corrections to Euler-scale GHD for the large-scale nonequilibrium dynamics of integrable systems, and arise due to two-body scatterings among quasiparticles. We give exact expressions for the diffusion coefficients. Our results apply to a large class of integrable models, including quantum and classical, Galilean and relativistic field theories, chains, and gases in one dimension, such as the Lieb-Liniger model describing cold atom gases and the Heisenberg quantum spin chain. We provide numerical evaluations in the Heisenberg $XXZ$ spin chain, both for the spin diffusion constant, and for the diffusive effects during the melting of a small domain wall of spins, finding excellent agreement with time-dependent density matrix renormalization group numerical simulations.

An analysis of a single-domain magnetic needle (MN) in the presence of an external magnetic field $\mathbf{B}$ is carried out with the aim of achieving a high-precision magnetometer. We determine the uncertainty $\mathrm{\Delta }B$ of such a device due to Gilbert dissipation and the associated internal magnetic field fluctuations that give rise to diffusion of the MN axis direction $\mathbf{n}$ and the needle orbital angular momentum. The levitation of the MN in a magnetic trap and its stability are also analyzed.

We propose a novel experiment to search for axion dark matter that differentiates the phase velocities of the left- and right-handed polarized photons. Our optical cavity measures the difference of the resonant frequencies between two circular polarizations of the laser beam. The design of our cavity adopts a double-pass configuration to realize a null experiment and give a high common mode rejection of environmental disturbances. We estimate the potential sensitivity to the axion-photon coupling constant $g_{a\gamma }$ for the axion mass $m\lesssim {10}^{-10}\mathrm{eV}$. In a low mass range $m\lesssim {10}^{-15}\mathrm{eV}$, we can achieve $g_{a\gamma }\lesssim 3\times {10}^{-16}{\mathrm{GeV}}^{-1}$, which is beyond the current bound by several orders of magnitude.

We show that the shape of the inflationary landscape potential may be constrained by analyzing cosmological data. The quantum fluctuations of fields orthogonal to the inflationary trajectory may have probed the structure of the local landscape potential, inducing non-Gaussianity (NG) in the primordial distribution of the curvature perturbations responsible for the cosmic microwave background (CMB) anisotropies and our Universe’s large-scale structure. The resulting type of NG (tomographic NG) is determined by the shape of the landscape potential, and it cannot be fully characterized by 3- or 4-point correlation functions. Here we deduce an expression for the profile of this probability distribution function in terms of the landscape potential, and we show how this can be inverted in order to reconstruct the potential with the help of CMB observations. While current observations do not allow us to infer a significant level of tomographic NG, future surveys may improve the possibility of constraining this class of primordial signatures.

The reactor antineutrino anomaly might be explained by the oscillation of reactor antineutrinos toward a sterile neutrino of eV mass. In order to explore this hypothesis, the STEREO experiment measures the antineutrino energy spectrum in six different detector cells covering baselines between 9 and 11 m from the compact core of the ILL research reactor. In this Letter, results from 66 days of reactor turned on and 138 days of reactor turned off are reported. A novel method to extract the antineutrino rates has been developed based on the distribution of the pulse shape discrimination parameter. The test of a new oscillation toward a sterile neutrino is performed by comparing ratios of cells, independent of absolute normalization and of the prediction of the reactor spectrum. The results are found to be compatible with the null oscillation hypothesis and the best fit of the reactor antineutrino anomaly is excluded at 97.5% C.L.