Motivated by a recent experiment in ultracold atoms [S. Krinner et al., Proc. Natl. Acad. Sci. U.S.A. 113, 8144 (2016)], we analyze transport of attractively interacting fermions through a one-dimensional wire near the superfluid transition. We show that in a ballistic regime where the conductance is quantized in the absence of interaction, the conductance is renormalized by superfluid fluctuations in reservoirs. In particular, the particle conductance is strongly enhanced, and the conductance plateau is blurred by emergent bosonic pair transport. For spin transport, in addition to the contact resistance, the wire itself is resistive, leading to a suppression of the measured spin conductance. Our results are qualitatively consistent with the experimental observations.

We demonstrate an all-optical method for manipulating the magnetization in a 1-mm yttrium-iron-garnet (YIG) sphere placed in a $\sim 0.17\mathrm{T}$ uniform magnetic field. A harmonic of the frequency comb delivered by a multi-GHz infrared laser source is tuned to the Larmor frequency of the YIG sphere to drive magnetization oscillations, which in turn give rise to a radiation field used to thoroughly investigate the phenomenon. The radiation damping issue that occurs at high frequency and in the presence of highly magnetizated materials has been overcome by exploiting the magnon-photon strong coupling regime in microwave cavities. Our findings demonstrate an effective technique for ultrafast control of the magnetization vector in optomagnetic materials via polarization rotation and intensity modulation of an incident laser beam. We eventually get a second-order susceptibility value of $\sim {10}^{-7}{\mathrm{cm}}^2/\mathrm{MW}$ for single crystal YIG.

Inelastic neutron scattering reveals a broad continuum of excitations in ${\mathrm{Pr}}_2{\mathrm{Zr}}_2{\mathrm{O}}_7$, the temperature and magnetic field dependence of which indicate a continuous distribution of quenched transverse fields ($\mathrm{\Delta }$) acting on the non-Kramers ${\mathrm{Pr}}^{3+}$ crystal field ground state doublets. Spin-ice correlations are apparent within 0.2 meV of the Zeeman energy. A random phase approximation provides an excellent account of the data with a transverse field distribution $\rho (\mathrm{\Delta })\propto ({\mathrm{\Delta }}^2+{\mathrm{\Gamma }}^2{)}^{-1}$, where $\mathrm{\Gamma }=0.27(1)\mathrm{meV}$. Established during high temperature synthesis due to an underlying structural instability, it appears disorder in ${\mathrm{Pr}}_2{\mathrm{Zr}}_2{\mathrm{O}}_7$ actually induces a quantum spin liquid.

We experimentally reveal the emergence of edge states in a photonic lattice with orbital bands. We use a two-dimensional honeycomb lattice of coupled micropillars whose bulk spectrum shows four gapless bands arising from the coupling of $p$-like photonic orbitals. We observe zero-energy edge states whose topological origin is similar to that of conventional edge states in graphene. Additionally, we report novel dispersive edge states in zigzag and armchair edges. The observations are reproduced by tight-binding and analytical calculations, which we extend to bearded edges. Our work shows the potentiality of coupled micropillars in elucidating some of the electronic properties of emergent two-dimensional materials with orbital bands.

In the study of open quantum systems, one of the most common ways to describe environmental effects on the reduced dynamics is through the spectral density. However, in many models this object cannot be computed from first principles and needs to be inferred on phenomenological grounds or fitted to experimental data. Consequently, some uncertainty regarding its form and parameters is unavoidable; this in turn calls into question the accuracy of any theoretical predictions based on a given spectral density. Here, we focus on the spin-boson model as a prototypical open quantum system, find two error bounds on predicted expectation values in terms of the spectral density variation considered, and state a sufficient condition for the strongest one to apply. We further demonstrate an application of our result, by bounding the error brought about by the approximations involved in the hierarchical equations of motion resolution method for spin-boson dynamics.

We consider the estimation of noise parameters in a quantum channel, assuming the most general strategy allowed by quantum mechanics. This is based on the exploitation of unlimited entanglement and arbitrary quantum operations, so that the channel inputs may be interactively updated. In this general scenario, we draw a novel connection between quantum metrology and teleportation. In fact, for any teleportation-covariant channel (e.g., Pauli, erasure, or Gaussian channel), we find that adaptive noise estimation cannot beat the standard quantum limit, with the quantum Fisher information being determined by the channel’s Choi matrix. As an example, we establish the ultimate precision for estimating excess noise in a thermal-loss channel, which is crucial for quantum cryptography. Because our general methodology applies to any functional that is monotonic under trace-preserving maps, it can be applied to simplify other adaptive protocols, including those for quantum channel discrimination. Setting the ultimate limits for noise estimation and discrimination paves the way for exploring the boundaries of quantum sensing, imaging, and tomography.

Quantum phase estimation is a fundamental subroutine in many quantum algorithms, including Shor’s factorization algorithm and quantum simulation. However, so far results have cast doubt on its practicability for near-term, nonfault tolerant, quantum devices. Here we report experimental results demonstrating that this intuition need not be true. We implement a recently proposed adaptive Bayesian approach to quantum phase estimation and use it to simulate molecular energies on a silicon quantum photonic device. The approach is verified to be well suited for prethreshold quantum processors by investigating its superior robustness to noise and decoherence compared to the iterative phase estimation algorithm. This shows a promising route to unlock the power of quantum phase estimation much sooner than previously believed.

We characterize the 795 nm ${{}^3\mathrm{H}}_6$ to ${{}^3\mathrm{H}}_4$ transition of ${\mathrm{Tm}}^{3+}$ in a ${\mathrm{Ti}}^{4+}:\mathrm{Li}\mathrm{Nb}{\mathrm{O}}_3$ waveguide at temperatures as low as 800 mK. Coherence and hyperfine population lifetimes—up to $117\mu \mathrm{s}$ and 2.5 h, respectively—exceed those at 3 K at least tenfold, and are equivalent to those observed in a bulk ${\mathrm{Tm}}^{3+}:\mathrm{Li}\mathrm{Nb}{\mathrm{O}}_3$ crystal under similar conditions. We also find a transition dipole moment that is equivalent to that of the bulk. Finally, we prepare a 0.5 GHz-bandwidth atomic frequency comb of finesse $>2$ on a vanishing background. These results demonstrate the suitability of rare-earth-ion-doped waveguides created using industry-standard Ti indiffusion in $\mathrm{Li}\mathrm{Nb}{\mathrm{O}}_3$ for on-chip quantum applications.

We present a simple and natural dark sector model in which dark matter particles arise as composite states of hidden strong dynamics and their stability is ensured by accidental symmetries. The model has only a few free parameters. In particular, the gauge symmetry of the model forbids the masses of dark quarks, and the confinement scale of the dynamics provides the unique mass scale of the model. The gauge group contains an Abelian symmetry $U(1{)}_D$, which couples the dark and standard model sectors through kinetic mixing. This model, despite its simple structure, has rich and distinctive phenomenology. In the case where the dark pion becomes massive due to $U(1{)}_D$ quantum corrections, direct and indirect detection experiments can probe thermal relic dark matter which is generically a mixture of the dark pion and the dark baryon, and the Large Hadron Collider can discover the $U(1{)}_D$ gauge boson. Alternatively, if the dark pion stays light due to a specific $U(1{)}_D$ charge assignment of the dark quarks, then the dark pion constitutes dark radiation. The signal of this radiation is highly correlated with that of dark baryons in dark matter direct detection.

Ion cyclotron emission (ICE) offers a unique promise as a diagnostic of the fusion born alpha-particle population in magnetically confined plasmas. Pioneering observations from JET and TFTR found that ICE intensity $P_{\mathrm{ICE}}$ scales approximately linearly with the measured neutron flux from fusion reactions, and with the inferred concentration, $n_{\alpha }/n_i$, of fusion born alpha particles confined within the plasma. We present fully nonlinear self-consistent kinetic simulations that reproduce this scaling for the first time. This resolves a long-standing question in the physics of fusion alpha-particle confinement and stability in magnetic confinement fusion plasmas. It confirms the magnetoacoustic cyclotron instability as the likely emission mechanism and greatly strengthens the basis for diagnostic exploitation of ICE in future burning plasmas.

We show how dispersionless channels exhibiting perfect spin-momentum locking can arise in a 1D lattice model. While such spectra are forbidden by fermion doubling in static 1D systems, here we demonstrate their appearance in the stroboscopic dynamics of a periodically driven system. Remarkably, this phenomenon does not rely on any adiabatic assumptions, in contrast to the well known Thouless pump and related models of adiabatic spin pumps. The proposed setup is shown to be experimentally feasible with state-of-the-art techniques used to control ultracold alkaline earth atoms in optical lattices.

We present a dynamic and thermodynamic study of the orientational glass former Freon 113 (1,1,2-trichloro-1,2,2-trifluoroethane, ${\mathrm{CCl}}_2\mathrm{F}\text{−}{\mathrm{CClF}}_2$) in order to analyze its kinetic and thermodynamic fragilities. Freon 113 displays internal molecular degrees of freedom that promote a complex energy landscape. Experimental specific heat and its microscopic origin, the vibrational density of states from inelastic neutron scattering, together with the orientational dynamics obtained by means of dielectric spectroscopy have revealed the highest fragility value, both thermodynamic and kinetic, found for this orientational glass former. The excess in both Debye-reduced specific heat and density of states (boson peak) evidences the existence of glassy low-energy excitations. We demonstrate that early proposed correlations between the boson peak and the Debye specific heat value are elusive as revealed by the clear counterexample of the studied case.

Most substitutional solutes in solids diffuse via vacancies. However, widely used analytic models for diffusivity make uncontrolled approximations in the relations between atomic jump rates that reduce accuracy. Symmetry analysis of the hexagonal close packed crystal identifies more distinct vacancy transitions than prior models, and a Green function approach computes diffusivity exactly for solutes in magnesium. We find large differences for the solute drag of Al, Zn, and rare earth solutes, and improved diffusion activation energies—highlighting the need for exact analytic transport models.

The Materials Project crystal structure database has been searched for materials possessing layered motifs in their crystal structures using a topology-scaling algorithm. The algorithm identifies and measures the sizes of bonded atomic clusters in a structure’s unit cell, and determines their scaling with cell size. The search yielded 826 stable layered materials that are considered as candidates for the formation of two-dimensional monolayers via exfoliation. Density-functional theory was used to calculate the exfoliation energy of each material and 680 monolayers emerge with exfoliation energies below those of already-existent two-dimensional materials. The crystal structures of these two-dimensional materials provide templates for future theoretical searches of stable two-dimensional materials. The optimized structures and other calculated data for all 826 monolayers are provided at our database (https://materialsweb.org).

We discuss that in the random phase approximation (RPA) the first derivative of the energy with respect to the Green’s function is the self-energy in the $GW$ approximation. This relationship allows us to derive compact equations for the RPA interatomic forces. We also show that position dependent overlap operators are elegantly incorporated in the present framework. The RPA force equations have been implemented in the projector augmented wave formalism, and we present illustrative applications, including ab initio molecular dynamics simulations, the calculation of phonon dispersion relations for diamond and graphite, as well as structural relaxations for water on boron nitride. The present derivation establishes a concise framework for forces within perturbative approaches and is also applicable to more involved approximations for the correlation energy.

Stimulated by experimental advances in electrolyte gating methods, we investigate theoretically percolation in thin films of inhomogeneous complex oxides, such as ${\mathrm{La}}_{1-x}{\mathrm{Sr}}_x{\mathrm{CoO}}_3$ (LSCO), induced by a combination of bulk chemical and surface electrostatic doping. Using numerical and analytical methods, we identify two mechanisms that describe how bulk dopants reduce the amount of electrostatic surface charge required to reach percolation: (i) bulk-assisted surface percolation and (ii) surface-assisted bulk percolation. We show that the critical surface charge strongly depends on the film thickness when the film is close to the chemical percolation threshold. In particular, thin films can be driven across the percolation transition by modest surface charge densities. If percolation is associated with the onset of ferromagnetism, as in LSCO, we further demonstrate that the presence of critical magnetic clusters extending from the film surface into the bulk results in considerable enhancement of the saturation magnetization, with pronounced experimental consequences. These results should significantly guide experimental work seeking to verify gate-induced percolation transitions in such materials.

We investigate the effect of ${\mathrm{Co}}^{2+}$ (spin-$1/2$) impurities on the magnetic ground state and low-lying spin excitations of the quasione-dimensional spin-$1/2$ antiferromagnet ${\mathrm{SrCuO}}_2$ by means of neutron scattering, muon spin spectroscopy, and bulk (ac and dc) magnetic susceptibilities. We found that dilute Co doping induces an Ising-like anisotropy and enhances the magnetic ordering temperature rather significantly, but preserves the gapless nature of the spin excitations. These results are in apparent contradiction with the recent studies of Ni (spin-1) doped ${\mathrm{SrCuO}}_2$. Low-temperature magnetic behavior of the Co-doped zigzag chains in ${\mathrm{SrCuO}}_2$ reveals the presence of a weak geometrical spin frustration.

We apply moderate-high-energy inelastic neutron scattering (INS) measurements to investigate ${\mathrm{Yb}}^{3+}$ crystalline electric field (CEF) levels in the triangular spin-liquid candidate ${\mathrm{YbMgGaO}}_4$. Three CEF excitations from the ground-state Kramers doublet are centered at the energies $\hslash \omega =39$, 61, and 97 meV in agreement with the effective spin-$1/2$ $g$ factors and experimental heat capacity, but reveal sizable broadening. We argue that this broadening originates from the site mixing between ${\mathrm{Mg}}^{2+}$ and ${\mathrm{Ga}}^{3+}$ giving rise to a distribution of Yb-O distances and orientations and, thus, of CEF parameters that account for the peculiar energy profile of the CEF excitations. The CEF randomness gives rise to a distribution of the effective spin-$1/2$ $g$ factors and explains the unprecedented broadening of low-energy magnetic excitations in the fully polarized ferromagnetic phase of ${\mathrm{YbMgGaO}}_4$, although a distribution of magnetic couplings due to the $\mathrm{Mg}/\mathrm{Ga}$ disorder may be important as well.