We report on previously unobserved intersystem degeneracies in two-component equal-mass Fermi gases with interspecies zero-range interactions under isotropic harmonic confinement. Over the past 10 years, two-component Fermi gases consisting of $n_1$ spin-up and $n_2$ spin-down atoms with interspecies zero-range interactions have become a paradigm for modeling condensed matter systems, nuclear matter, and neutron matter. We show that the eigenenergies of the $(n_1+1,n_2-1)$ system are degenerate with the eigenenergies of the $(n_1,n_2)$ system for any $s$-wave scattering length $a_s$, including infinitely large, positive, and negative $a_s$. The existence of the intersystem degeneracies is demonstrated explicitly for few-body systems with $n_1+n_2=4$, 5, and 6. The degeneracies and associated symmetries are explained within a group theoretical framework.

Gaussian quantum discord is a measure of quantum correlations in Gaussian systems. Using Gaussian discord, we quantify the quantum correlations of a bipartite entangled state and a separable two-mode mixture of coherent states. We experimentally analyze the effect of noise addition and dissipation on Gaussian discord and show that the former noise degrades the discord, while the latter noise for some states leads to an increase of the discord. In particular, we experimentally demonstrate the near death of discord by noisy evolution and its revival through dissipation.

We develop a diagrammatic scattering theory for interacting bosons in a three-dimensional, weakly disordered potential. We show how collisional energy transfer between the bosons induces the thermalization of the inelastic single-particle current which, after only a few collision events, dominates over the elastic contribution described by the Gross-Pitaevskii ansatz.

We investigate properties of the inner horizons of certain black holes in higher-derivative three-dimensional gravity theories. We focus on Bañados-Teitelboim-Zanelli and spacelike warped anti–de Sitter black holes, as well as on asymptotically warped de Sitter solutions exhibiting both a cosmological and a black hole horizon. We verify that a first law is satisfied at the inner horizon, in agreement with the proposal of Castro and Rodriguez [arXiv:1204.1284]. We then show that, in topologically massive gravity, the product of the areas of the inner and outer horizons fails to be independent on the mass, and we trace this to the diffeomorphism anomaly of the theory.

New physics that exhibits irregular tracks such as kinks, intermittent hits, or decay in flight may easily be missed at hadron colliders. We demonstrate this by studying viable models of light, $\mathcal{O}(10\mathrm{GeV})$, colored particles that decay predominantly inside the tracker. Such particles can be produced at staggering rates, and yet, may not be identified or triggered on at the LHC, unless specifically searched for. In addition, the models we study provide an explanation for the original measurement of the anomalous charged track distribution by CDF. The presence of irregular tracks in these models reconcile that measurement with the subsequent reanalysis and the null results of ATLAS and CMS. Our study clearly illustrates the need for a comprehensive study of irregular tracks at the LHC.

We employ interactions from chiral effective field theory and compute the binding energies and low-lying excitations of calcium isotopes with the coupled-cluster method. Effects of three-nucleon forces are included phenomenologically as in-medium two-nucleon interactions, and the coupling to the particle continuum is taken into account using a Berggren basis. The computed ground-state energies and the low-lying $J^{\pi }=2^{+}$ states for the isotopes ${}^{42,48,50,52}\mathrm{Ca}$ are in good agreement with data, and we predict the excitation energy of the first $J^{\pi }=2^{+}$ state in ${}^{54}\mathrm{Ca}$ at 1.9 MeV, displaying only a weak subshell closure. In the odd-mass nuclei ${}^{53,55,61}\mathrm{Ca}$ we find that the positive parity states deviate strongly from the naive shell model.

The shell model Monte Carlo method is a powerful technique to calculate thermal and ground-state properties of strongly correlated finite-size systems. However, its application to odd-particle-number systems has been hampered by the sign problem that originates from the projection on an odd number of particles. We circumvent this sign problem for the ground-state energy by extracting the ground-state energy of the odd-particle-number system from the asymptotic behavior of the imaginary-time single-particle Green’s function of the even-particle-number system. We apply this method to calculate pairing gaps of nuclei in the iron region. Our results are in good agreement with experimental pairing gaps.

We demonstrate efficient heralded generation of high purity narrow-bandwidth single photons from a transient collective spin excitation in a hot atomic vapor cell. Employing optical homodyne tomography, we fully reconstruct the density matrix of the generated photon and observe a Wigner function reaching the zero value without correcting for any inefficiencies. The narrow bandwidth of the photon produced is accompanied by a high generation rate yielding a high spectral brightness. The source is, therefore, compatible with atomic-based quantum memories as well as other applications in light-atom interfacing. This Letter paves the way to preparing and measuring arbitrary superposition states of collective atomic excitations.

We propose a realistic circuit QED experiment to test the extraction of past-future vacuum entanglement to a pair of superconducting qubits. The qubit $P$ interacts with the quantum field along an open transmission line for an interval $T_{\mathrm{on}}$ and then, after a time-lapse $T_{\mathrm{off}}$, the qubit $F$ starts interacting for a time $T_{\mathrm{on}}$ in a symmetric fashion. After that, past-future quantum correlations will have transferred to the qubits, even if the qubits do not coexist at the same time. We show that this experiment can be realized with current technology and discuss its utility as a possible implementation of a quantum memory.

Spatial periodic forcing of pattern-forming systems is an important, but lightly studied, method of controlling patterns. It can be used to control the amplitude and wave number of one-dimensional periodic patterns, to stabilize unstable patterns, and to induce them below instability onset. We show that, although in one spatial dimension the forcing acts to reinforce the patterns, in two dimensions it acts to destabilize or displace them by inducing two-dimensional rectangular and oblique patterns.

We study the long-term average frequency as a function of the natural frequency for Kuramoto oscillators with periodic coefficients. Unlike the case for more general periodically forced oscillators, this function is never a “devil’s staircase”; it may have plateaus at integer multiples of the forcing frequency, but we prove it is strictly increasing between these plateaus. The proof uses the fact that the flow maps for Kuramoto oscillators extend to Möbius transformations on the complex plane, and that Möbius transformations have particularly simple dynamics that rule out $p:q$ mode locking except in the case of fixed points ($q=1$). We also give a criterion for the degeneration of an integer plateau to a single point and use it to explain the absence of plateaus at even multiples of the collective frequency for a Kuramoto system with a bimodal frequency distribution.

Hydrodynamic synchronization is a fundamental physical phenomenon by which self-sustained oscillators communicate through perturbations in the surrounding fluid and converge to a stable synchronized state. This is an important factor for the emergence of regular and coordinated patterns in the motions of cilia and flagella. When dealing with biological systems, however, it is always hard to disentangle internal signaling mechanisms from external purely physical couplings. We have used the combination of two-photon polymerization and holographic optical trapping to build a mesoscale model composed of chiral propellers rotated by radiation pressure. The two microrotors can be synchronized by hydrodynamic interactions alone although the relative torques have to be finely tuned. Dealing with a micron sized system we treat synchronization as a stochastic phenomenon and show that the phase lag between the two microrotors is distributed according to a stationary Fokker-Planck equation for an overdamped particle over a tilted periodic potential. Synchronized states correspond to minima in this potential whose locations are shown to depend critically on the detailed geometry of the propellers.

We report on the first quantitative test of acoustic orbital angular momentum transfer to a sound absorbing object immersed in a viscous liquid. This is done by realizing an original experiment that is to spin a millimeter-size target disk using an ultrasonic vortex beam. We demonstrate the balance between the acoustic radiation torque calculated from the Brillouin stress tensor and the viscous torque evaluated from the steady state spinning frequency. Moreover, we unveil a rotational acoustic streaming phenomenon that results from the acoustic angular momentum transfer to the host fluid. We show that it lowers the viscous torque, thereby restoring the torque balance.

Since the advent of theoretical materials science some 60 years ago, there has been a drive to predict and design new materials in silicio. Mathematical optimization procedures to determine phase stability can be generally applicable to complex ternary or higher-order materials systems where the phase diagrams of the binary constituents are sufficiently known. Here, we employ a simplex-optimization procedure to predict new compounds in the ternary Nb-Ge-C system. Our theoretical results show that the hypothetical ${\mathrm{Nb}}_2\mathrm{GeC}$ is stable, and excludes all reasonably conceivable competing hypothetical phases. We verify the existence of the ${\mathrm{Nb}}_2\mathrm{GeC}$ phase by thin film synthesis using magnetron sputtering. This hexagonal nanolaminated phase has $a$ and $c$ lattice parameters of $\sim 3.24\AA$ and 12.82 Å.

Using first-principles atomistic simulations, we study the response of atomically thin layers of transition metal dichalcogenides (TMDs)—a new class of two-dimensional inorganic materials with unique electronic properties—to electron irradiation. We calculate displacement threshold energies for atoms in 21 different compounds and estimate the corresponding electron energies required to produce defects. For a representative structure of ${\mathrm{MoS}}_2$, we carry out high-resolution transmission electron microscopy experiments and validate our theoretical predictions via observations of vacancy formation under exposure to an 80 keV electron beam. We further show that TMDs can be doped by filling the vacancies created by the electron beam with impurity atoms. Thereby, our results not only shed light on the radiation response of a system with reduced dimensionality, but also suggest new ways for engineering the electronic structure of TMDs.

Theoretical studies of localization, anomalous diffusion and ergodicity breaking require solving the electronic structure of disordered systems. We use free probability to approximate the ensemble-averaged density of states without exact diagonalization. We present an error analysis that quantifies the accuracy using a generalized moment expansion, allowing us to distinguish between different approximations. We identify an approximation that is accurate to the eighth moment across all noise strengths, and contrast this with perturbation theory and isotropic entanglement theory.

Measurements on very low disorder two-dimensional electrons confined to relatively wide GaAs quantum well samples with tunable density reveal a close competition between the electron liquid and solid phases near the Landau level filling factor $\nu =1$. As the density is raised, the fractional quantum Hall liquid at $\nu =4/5$ suddenly disappears at a well-width dependent critical density, and then reappears at higher densities with insulating phases on its flanks. These insulating phases exhibit reentrant $\nu =1$ integer quantum Hall effects and signal the formation of electron Wigner crystal states. Qualitatively similar phenomena are seen near $\nu =6/5$.

We demonstrate that nearly critical quantum magnetic fluctuations in strongly correlated electron systems can change the Fermi surface topology and also lead to spin charge separation in two dimensions. To demonstrate these effects, we consider a small number of holes injected into the bilayer antiferromagnet. The system has a quantum critical point (QCP) which separates magnetically ordered and disordered phases. We demonstrate that in the physically interesting regime, there is a magnetically driven Lifshitz point (LP) inside the magnetically disordered phase. At the LP, the topology of the hole Fermi surface is changed. We also demonstrate that in this regime, the hole spin and charge necessarily separate when approaching the QCP. The considered model sheds light on generic problems concerning the physics of the cuprates.

We report the doping, temperature, and spatial evolutions of the electronic structure of ${\mathrm{NaFe}}_{1-x}{\mathrm{Co}}_x\mathrm{As}$ studied by scanning tunneling microscopy. In the parent state we directly observe the spin density wave gap, which exhibits unconventional features that are incompatible with simple Fermi surface nesting. The optimally doped sample has a single superconducting gap, but in the overdoped regime a novel pseudogaplike feature emerges. The pseudogaplike phase coexists with superconductivity in the ground state, persists well into the normal state, and shows strong spatial variations. The characteristics of the three distinct electronic states revealed here shed important new lights on the microscopic models for the iron-based superconductors.

We study the emission of quasiparticles in the scaling limit of the 1D quantum Ising chain at the critical point perturbed by a time-dependent local transverse field. We compute exactly and for a generic time dependence the average value of the transverse magnetization, its correlation functions, as well as the statistics of both the inclusive and exclusive work. We show that, except for a cyclic perturbation, the probability distribution of the work at low energies is a power law whose exponent is universal, i.e., does not depend on the specific time-dependent protocol, but only on the final value attained by the perturbation.