A two-parameter fractional statistics is proposed, which can be used to model a weakly interacting Bose system. It is shown that the parameters of the introduced weakly nonadditive Polychronakos statistics can be linked to the effects of interactions as well as to finite-size corrections. Calculations are made of the specific heat and condensate fraction of the model system corresponding to harmonically trapped Rb-87 atoms. The behavior of the specific heat of three-dimensional isotropic harmonic oscillators with respect tothe statistics parameters is studied in the temperature domain including the BEC-like phase-transition point.

Probabilistic metrology attempts to improve parameter estimation by occasionally reporting an excellent estimate and the rest of the time either guessing or doing nothing at all. Here we show that probabilistic metrology can never improve quantum limits on estimation of a single parameter, both on average and asymptotically in number of trials, if performance is judged relative to mean-square estimation error. We extend the result by showing that for a finite number of trials, the probability of obtaining better estimates using probabilistic metrology, as measured by mean-square error, decreases exponentially with the number of trials. To be tight, the performance bounds we derive require that likelihood functions be approximately normal, which in turn depends on how rapidly specific distributions converge to a normal distribution with number of trials.

We determine the secrecy capacity of the compound channel with quantum wiretapper and channel state information at the transmitter. Moreover, we derive a lower bound on the secrecy capacity of this channel without channel state information and determine the secrecy capacity of the compound classical-quantum wiretap channel with channel state information at the transmitter. We use this result to derive a proof for a lower bound on the entanglement generating capacity of the compound quantum channel. We also derive a proof for the formula for entanglement generating capacity of the compound quantum channel with channel state information at the encoder which was given in additional information [Bjelaković, Boche, and Nötzel, in Proceedings of International Symposium on Information Theory ISIT, Korea, 2009 (IEEE, New York, 2009), pp. 1889–1893].

The isotope effects in ${\mathrm{Si}}^{-}$ bound levels are studied using the multiconfiguration Hartree-Fock ab initio approach. Large-scale calculations are carried out for the $3p^3{}^4{S}^o$, ${}^2{D}^o$, and ${}^2{P}^o$ multiplets of ${\mathrm{Si}}^{-}$ and the $3p^2{}^{3}P$ multiplet of Si. We predict an anomalous isotope shift on the electron affinity, dominated by the specific mass shift, with a value of $-0.66\left(6\right)$ m${}^{-1}$ for the 30-28 isotope pair. We also report hyperfine-structure parameters for the studied multiplets. We provide the values of level electric-field gradients at the nucleus that could be of interest in a study of the metastable silicon isotopes. Relativistic corrections are estimated using nonrelativistic orbitals in the Breit-Pauli and fully relativistic frameworks.

A multicenter distorted-wave (MCDW) method for fast-electron-impact single ionization of a molecular system in the coplanar-asymmetric kinematics is developed. Plane waves are used to describe the fast incoming and outgoing electrons and the multicenter nature of the molecule is considered by describing the slow ejected electron with the multicenter distorted wave, which is solved from the anisotropic multicenter potential between the ejected electron and the ionic molecule. The MCDW method improves the conventional molecular distorted-wave methods, whose distorted wave is solved from the spherically averaged isotropic potential. The application to the water molecule shows reasonable agreement with the available experimental data.

We demonstrate slowing and longitudinal cooling of a supersonic beam of CaF molecules using counterpropagating laser light resonant with a closed rotational and almost-closed vibrational transition. A group of molecules are decelerated by about 20 m/s by applying light of a fixed frequency for 1.8 ms. Their velocity spread is reduced, corresponding to a final temperature of about 300 mK. The velocity is further reduced by chirping the frequency of the light to keep it in resonance as the molecules slow down.

Recent experimental advances enabled the realization of mobile impurities immersed in a Bose-Einstein condensate (BEC) of ultracold atoms. Here, we consider impurities with two or more internal hyperfine states, and study their radio-frequency (rf) absorption spectra, which correspond to transitions between two different hyperfine states. We calculate rf spectra for the case when one of the hyperfine states involved interacts with the BEC, while the other state is noninteracting, by performing a nonperturbative resummation of the probabilities of exciting different numbers of phonon modes. In the presence of interactions, the impurity gets dressed by Bogoliubov excitations of the BEC, and forms a polaron. The rf signal contains a $\delta$-function peak centered at the energy of the polaron measured relative to the bare impurity transition frequency with a weight equal to the amount of bare impurity character in the polaron state. The rf spectrum also has a broad incoherent part arising from the background excitations of the BEC, with a characteristic power-law tail that appears as a consequence of the universal physics of contact interactions. We discuss both the direct rf measurement, in which the impurity is initially in an interacting state, and the inverse rf measurement, in which the impurity is initially in a noninteracting state. In the latter case, in order to calculate the rf spectrum, we solve the problem of polaron formation: a mobile impurity is suddenly introduced in a BEC, and dynamically gets dressed by Bogoliubov phonons. Our solution is based on a time-dependent variational ansatz of coherent states of Bogoliubov phonons, which becomes exact when the impurity is localized. Moreover, we show that such an ansatz compares well with a semiclassical estimate of the propagation amplitude of a mobile impurity in the BEC. Our technique can be extended to cases when both initial and final impurity states are interacting with the BEC.

The recent experimental realization of spin-orbit (SO) coupling for ultracold atoms opens a completely new avenue for exploring new quantum matters. In experiments, the SO coupling is implemented simultaneously with a Zeeman field. Such SO-coupled Fermi gases are predicted to support Majorana fermions with non-Abelian exchange statistics in one dimension (1D). However, as shown in recent theory and experiments for 1D spin-imbalanced Fermi gases, the Zeeman field can lead to the long-sought Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superfluids with nonzero center-of-mass momentum Cooper pairings, in contrast to the zero center-of-mass momentum pairings in Majorana superfluids. Therefore a natural question to ask is which phase, FFLO or Majorana superfluids, will survive in SO-coupled Fermi gases in the presence of a large out-of-plane Zeeman field. In this paper, we address this question by studying the mean-field quantum phases of 1D (quasi-1D) SO-coupled fermionic cold-atom optical lattices.

We consider a coupled-cavity array (CCA), where one cavity interacts with a two-level atom under the rotating-wave approximation. We investigate the excitation transport dynamics across the array, which arises in the atom's emission process into the CCA vacuum. Due to the known formation of atom-photon bound states, partial field localization and atomic population trapping in general take place. We study the functional dependence on the coupling strength of these two phenomena and show that the threshold values beyond which they become significant are different. As the coupling strength grows from zero, field localization is exhibited first.

An incomplete quantum measurement can induce nontrivial dynamics between degenerate subspaces, a closed sequence of such projections produces a nonabelian holonomy. We show how to induce unitary evolution on an initial subspace from such finite discrete sequences and also construct a near deterministic repeat-until-success protocol. We also prove necessary and sufficient criteria on the auxiliary Hilbert space dimension required for inducing isometries between subspaces.

The Landau-Zener formula provides an analytical expression for the final excitation of a quantum system after passage of an avoided crossing of two energy levels. If the two levels correspond to a ground state and to an excited state which is subject to radiative decay, the probability of exciting the system by adiabatic passage of the level crossing is reduced. In this article we use a stochastic master equation to study the level crossing dynamics when the system is subject to continuous probing of the emitted radiation. The measurement back action on the system associated with the fluctuating homodyne detection record alters the level crossing dynamics, leading to significant excitation in spite of decay and imperfect transfer.

We analyze entropic uncertainty relations in a finite-dimensional Hilbert space and derive several strong bounds for the sum of two entropies obtained in projective measurements with respect to any two orthogonal bases. We improve the recent bounds by Coles and Piani [P. Coles and M. Piani, Phys. Rev. A 89, 022112 (2014)], which are known to be stronger than the well-known result of Maassen and Uffink [H. Maassen and J. B. M. Uffink, Phys. Rev. Lett. 60, 1103 (1988)]. Furthermore, we find a bound based on majorization techniques, which also happens to be stronger than the recent results involving the largest singular values of submatrices of the unitary matrix connecting both bases. The first set of bounds gives better results for unitary matrices close to the Fourier matrix, while the second one provides a significant improvement in the opposite sectors. Some results derived admit generalization to arbitrary mixed states, so that corresponding bounds are increased by the von Neumann entropy of the measured state. The majorization approach is finally extended to the case of several measurements.

In this article we investigate the dynamics of a single negatively charged nitrogen-vacancy center (NV${}^{-}$) coupled to the spin of the nucleus of a 15-nitrogen atom and show that high-speed, high-fidelity gate operations are possible without the need for complicated composite pulse sequences. These operations include both the electron and nuclear spin rotations, as well as an entangling gate between them. These are the primitive gates one will need within a quantum node of a distributed communication network.

We present a scheme of quantum simulation of many-body interactions with trapped ions via the exchange of virtual phonons, where the motion from both the longitudinal and the transverse directions is considered. By tuning the detunings of Raman lasers, the long-range and locally tunable interaction is easily obtained between different spins. We show that the competing spin-spin couplings mediated by all motion modes can give rise to higher levels of frustration and richer phase transitions than the conventional approaches based on the longitudinal or the transverse phonon modes alone.

The structural study of entanglement in multipartite systems is hindered by the lack of necessary and sufficient operational criteria able to discriminate among the various entanglement properties of a given mixed state. Here, we pursue a different route to the study of multipartite entanglement based on the closeness of a multipartite state to the set of separable ones. In particular, we analyze multipartite diagonal symmetric $N$-qubit states and provide the analytical expression for their best separable approximation (BSA, [Phys. Rev. Lett. 80, 2261 (1998)]), that is, their unique convex decomposition into a separable part and an entangled part, with maximal weight of the separable part.

Using the recently proposed theory, we calculate thermal effect in the Casimir interaction from graphene-coated metallic and dielectric substrates. The cases when only one or both of the two parallel plates are coated with graphene are considered. It is shown that the graphene coating does not influence the Casimir interaction between metals but produces a large impact for dielectrics. This impact increases with decreasing static dielectric permittivity of the plate material. The thermal correction to the gradient of the Casimir force between a Au sphere and a graphene-coated fused-silica plate is calculated. It is shown to be significantly greater than the total experimental error in the recently performed experiment, which is demonstrated to be only one step away from observation of the thermal effect from a graphene-coated substrate at short separation distances. To achieve this goal, one should increase the thickness of the fused-silica film from 300 nm to $2\mu$m.

We study the quantum scattering in two spatial dimensions without the usual partial-wave formalism. The analysis beyond the partial-wave approximation allows a quantitative treatment of the anisotropic scattering with a strong coupling of different angular momenta nonvanishing even at the zero-energy limit. High efficiency of our method is demonstrated for the two-dimensional (2D) scattering on the cylindrical potential with the elliptical base and dipole-dipole collisions in the plane. We reproduce the result for the 2D scattering of polarized dipoles in binary collisions obtained recently by Ticknor [Phys. Rev. A 84, 032702 (2011)] and explore the 2D collisions of unpolarized dipoles.

We present intensity-resolved above-threshold ionization (ATI) spectra of xenon using an intensity scanning and deconvolution technique. Experimental data were obtained with laser pulses of 58 fs and a central wavelength of 800 nm from a chirped-pulse amplifier. Applying a deconvolution algorithm, we obtained spectra that have higher contrast and are in excellent agreement with characteristic two and ten $U_p$ cutoff energies contrary to that found for raw data. The retrieved electron-ionization probability is consistent with the presence of a second electron from double ionization. This recovered ionization probability is confirmed with a calculation based on the Perelomov, Popov, and Terent'ev tunneling ionization model [Sov. Phys. JETP 23, 924 (1966)]. Thus, the measurements of the photoelectron yields and the developed deconvolution technique allowed retrieval of more accurate spectroscopic information from the ATI spectra and ionization probability features that usually are concealed by volume averaging.