We study the phase space distribution of an optomechanical cavity near the threshold of self-excited oscillation. A fully on-fiber optomechanical cavity is fabricated by patterning a suspended metallic mirror on the tip of the fiber. Optically induced self-excited oscillation of the suspended mirror is observed above a threshold value of the injected laser power. A theoretical analysis based on the Fokker-Planck equation evaluates the expected phase space distribution near threshold. A tomography technique is employed for extracting phase space distribution from the measured reflected optical power vs time in steady state. Comparison between theory and experimental results allows the extraction of the device parameters.

We demonstrate a high-efficiency deterministic quantum receiver to convert flying qubits to stationary qubits. We employ a superconducting resonator, which is driven with a shaped pulse through an adjustable coupler. For the ideal “time-reversed” shape, we measure absorption and receiver fidelities at the single microwave photon level of, respectively, 99.41% and 97.4%. These fidelities are comparable with gates and measurement and exceed the deterministic quantum communication and computation fault-tolerant thresholds, enabling new designs of deterministic qubit interconnects and hybrid quantum computers.

Grover’s quantum search algorithm can be formulated as a quantum particle randomly walking on the (highly symmetric) complete graph, with one vertex marked by a nonzero potential. From an initial equal superposition, the state evolves in a two-dimensional subspace. Strongly regular graphs have a local symmetry that ensures that the state evolves in a three-dimensional subspace but most have no global symmetry. Using degenerate perturbation theory, we show that quantum random walk search on known families of strongly regular graphs, nevertheless, achieves the full quantum speed-up of $\mathrm{\Theta }(\sqrt{N})$, disproving the intuition that fast quantum search requires global symmetry.

Lieb-Robinson-type bounds are reported for a large class of classical Hamiltonian lattice models. By a suitable rescaling of energy or time, such bounds can be constructed for interactions of arbitrarily long range. The bound quantifies the dependence of the system’s dynamics on a perturbation of the initial state. The effect of the perturbation is found to be effectively restricted to the interior of a causal region of logarithmic shape, with only small, algebraically decaying effects in the exterior. A refined bound, sharper than conventional Lieb-Robinson bounds, is required to correctly capture the shape of the causal region, as confirmed by numerical results for classical long-range $XY$ chains. We discuss the relevance of our findings for the relaxation to equilibrium of long-range interacting lattice models.

The radionuclide ${}^{60}\mathrm{Fe}$ has been of great interest to the nuclear astrophysics community for over a decade. An initial discrepancy between the observed and modeled Galactic ${}^{60}\mathrm{Fe}/{}^{26}\mathrm{Al}$ ratio motivated numerous studies focused on the nucleosynthesis of these two isotopes, though the cross section of the primary astrophysical production reaction, ${}^{59}\mathrm{Fe}(n,\gamma ){}^{60}\mathrm{Fe}$, has remained purely theoretical. The present work offers a first experimental constraint on the ${}^{59}\mathrm{Fe}(n,\gamma ){}^{60}\mathrm{Fe}$ cross section at astrophysical energies, obtained indirectly via Coulomb dissociation, and demonstrates that the theoretical reaction rates used in present stellar models are not highly erroneous.

We use inelastic neutron scattering to study spin waves in the antiferromagnetic ordered phase of iron pnictide NaFeAs throughout the Brillouin zone. Comparing with the well-studied $A{\mathrm{Fe}}_2{\mathrm{As}}_2$ ($A=\mathrm{Ca}$, Sr, Ba) family, spin waves in NaFeAs have considerably lower zone boundary energies and more isotropic effective in-plane magnetic exchange couplings. These results are consistent with calculations from a combined density functional theory and dynamical mean field theory and provide strong evidence that pnictogen height controls the strength of electron-electron correlations and consequently the effective bandwidth of magnetic excitations.

We consider the decay of a generic resonance to two visible particles and any number of invisible particles. We show that the shape of the invariant mass distribution of the two visible particles is sensitive to both the mass spectrum of the new particles, as well as the decay topology. We provide the analytical formulas describing the invariant mass shapes for the nine simplest topologies (with up to two invisible particles in the final state). Any such distribution can be simply categorized by its end point, peak location, and curvature, which are typically sufficient to discriminate among the competing topologies. In each case, we list the effective mass parameters which can be measured by experiment. In certain cases, the invariant mass shape is sufficient to completely determine the new particle mass spectrum, including the overall mass scale.

We argue that the study of heavy quarkonia, in particular that of $\mathrm{{\rm Y}}$, produced back to back with an isolated photon in $pp$ collisions at the LHC is the best—and currently unique—way to access the distribution of both the transverse momentum and the polarization of the gluon in an unpolarized proton. These encode fundamental information on the dynamics of QCD. We derive analytical expressions for various transverse-momentum distributions that can be measured at the LHC and which allow for a direct extraction of the aforementioned quantities. To assess the feasibility of such measurements, we evaluate the expected yields and the relevant transverse-momentum distributions for different models of the gluon dynamics inside a proton.

The ${\frac{1}{2}}^{+}\to {\frac{1}{2}}^{+}$ superallowed mixed mirror decay of ${}^{19}\mathrm{Ne}$ to ${}^{19}\mathrm{F}$ is excellently suited for high precision studies of the weak interaction. However, there is some disagreement on the value of the half-life. In a new measurement we have determined this quantity to be $T_{1/2}=17.2832\pm 0.0051_{\text{(stat)}}\pm 0.0066_{\text{(syst)}}\mathrm{s}$, which differs from the previous world average by 3 standard deviations. The impact of this measurement on limits for physics beyond the standard model such as the presence of tensor currents is discussed.

We show analytically and through three-dimensional particle-in-cell simulations that nonlinear wakefields driven by Laguerre-Gaussian laser pulses can lead to hollow electron self-injection and positron acceleration. We find that higher order lasers can drive donut shaped blowout wakefields with strong positron accelerating gradients comparable to those of a spherical bubble. Corresponding positron focusing forces can be more than an order of magnitude stronger than electron focusing forces in a spherical bubble. Required laser intensities and energies to reach the nonlinear donut shaped blowout are within state-of-the-art experimental conditions.

We predict the existence of a self-localized solution in a nonresonantly pumped exciton-polariton condensate. The solution has a shape resembling the well-known hyperbolic tangent profile of a dark soliton, but exhibits several distinct features. We find that it performs small oscillations, which are transformed into “soliton explosions” at lower pumping intensities. Moreover, after hundreds or thousands of picoseconds of apparently stable evolution the soliton decays abruptly, which is explained by the acceleration instability found previously in the Bekki-Nozaki hole solutions of the complex Ginzburg-Landau equation. We show that the soliton can be formed spontaneously from a small seed in the polariton field or by using spatial modulation of the pumping profile.

The temperature dependent Hall mobility data from La-doped ${\mathrm{SrTiO}}_3$ thin films are analyzed and modeled considering various electron scattering mechanisms. We find that a $\sim 6\mathrm{meV}$ transverse optical phonon deformation potential scattering mechanism is necessary to explain the dependence of transport on temperature between 10–200 K. Also, we find that the low temperature electron mobility in intrinsic (nominally undoped) ${\mathrm{SrTiO}}_3$ is limited by acoustic phonon scattering. Adding the above two scattering mechanisms to longitudinal optical phonon and ionized impurity scattering mechanisms, excellent quantitative agreement between mobility measurement and model is achieved in the whole temperature range (2–300 K) and carrier concentrations ranging over a few orders of magnitude ($8\times {10}^{17}–2\times {10}^{20}{\mathrm{cm}}^{-3}$).

We propose a conceptually new way to gather information on the electron bands of buried metal-(semiconductor-)insulator interfaces. The bias dependence of low frequency noise in ${\mathrm{Fe}}_{1-x}{\mathrm{V}}_x/\mathrm{MgO}/\mathrm{Fe}(0<x<0.25)$ tunnel junctions shows clear anomalies at specific applied voltages, reflecting electron tunneling to the band edges of the magnetic electrodes. The change in magnitude of these noise anomalies with the magnetic state allows evaluating the degree of spin mixing between the spin polarized bands at the ferromagnet-insulator interface. Our results are in qualitative agreement with numerical calculations.

We provide an exact description of out-of-equilibrium fixed points in quantum impurity models that is able to treat time-dependent forcing. Building on this, we then show that analytical out-of-equilibrium results that exactly treat interactions can be obtained in interacting quantum impurity models in their strong-coupling regime, provided they are integrable at equilibrium and they are “super Fermi liquids”; i.e., they only allow for integer charge hopping. For such systems we build an out-of-equilibrium strong-coupling expansion, akin to a Sommerfeld expansion in interacting systems. We apply our approach to the interacting resonant level model, and obtain the exact expansion around the low energy fixed point of the universal scaling function for the charge current as a function of voltage, temperature, and frequency, up to order 7.

Both quantum spin Hall and quantum anomalous Hall states are novel states of quantum matter with promising applications. We propose junction quantum wells comprising II-VI, III-V, or IV semiconductors as a large class of new materials realizing the quantum spin Hall state. Especially, we find that the bulk band gap for the quantum spin Hall state can be as large as 0.1 eV. Furthermore, magnetic doping would induce the ferromagnetism in these junction quantum wells due to band edge singularities in the band-inversion regime and to realize the quantum anomalous Hall state.

We study itinerant ferromagnetism in multiorbital Hubbard models in certain two-dimensional square and three-dimensional cubic lattices. In the strong coupling limit where doubly occupied orbitals are not allowed, we prove that the fully spin-polarized states are the unique ground states, apart from the trivial spin degeneracies, for a large region of filling factors. Possible applications to $p$-orbital bands with ultracold fermions in optical lattices, and electronic $3d$-orbital bands in transition-metal oxides, are discussed.