Balanced electric-magnetic dihole in Kaluza-Klein theory

We present a four-dimensional double-black-hole (or dihole) solution in Kaluza-Klein theory, describing a superposition of an electrically charged and a magnetically charged black hole. This system can be balanced for appropriately chosen parameters, and the resulting space-time is completely regular on and outside the event horizons. This solution was constructed using the inverse-scattering method in five-dimensional vacuum gravity, in which it describes a rotating black ring surrounding a static black hole on a Taub-NUT background space. Various properties of this solution are studied, from both a four- and five-dimensional perspective.Comment: 33 pages, 6 figures; v2: expanded discussion of phase space, published versio

Multipartite quantum nonlocality under local decoherence

We study the nonlocal properties of two-qubit maximally-entangled and N-qubit Greenberger-Horne-Zeilinger states under local decoherence. We show that the (non)resilience of entanglement under local depolarization or dephasing is not necessarily equivalent to the (non)resilience of Bell-inequality violations. Apart from entanglement and Bell-inequality violations, we consider also nonlocality as quantified by the nonlocal content of correlations, and provide several examples of anomalous behaviors, both in the bipartite and multipartite cases. In addition, we study the practical implications of these anomalies on the usefulness of noisy Greenberger-Horne-Zeilinger states as resources for nonlocality-based physical protocols given by communication complexity problems. There, we provide examples of quantum gains improving with the number of particles that coexist with exponentially-decaying entanglement and non-local contents.Comment: 6 pages, 4 figure

Thermal-assisted Anisotropy and Thermal-driven Instability in the Superfluidity state of Two-Species Polar Fermi Gas

We study the superfluid state of two-species heteronuclear Fermi gases with isotropic contact and anisotropic long-range dipolar interactions. By explicitly taking account of Fock exchange contribution, we derive self-consistent equations describing the pairing states in the system. Exploiting the symmetry of the system, we developed an efficient way of solving the self-consistent equations by exploiting the symmetries. We find that the temperature tends to increase the anisotropy of the pairing state, which is rather counterintuitive. We study the anisotropic properties of the system by examining the angular dependence of the number density distribution, the excitation spectrum and the pair correlation function. The competing effects of the contact interaction and the dipolar interaction upon the anisotropy are revealed. We derive and compute the superfluid mass density $\rho_{ij}$ for the system. Astonishingly, we find that $\rho_{zz}$ becomes negative above some certain temperature $T^*$($T<T_c$), signaling some instability of the system. This suggests that the elusive FFLO state may be observed in experiments, due to an anisotropic state with a spontaneously generated superflow.Comment: 7 pages, 5 figure

Multi-threshold second-order phase transition

We present a theory of the multi-threshold second-order phase transition, and experimentally demonstrate the multi-threshold second-order phase transition phenomenon. With carefully selected parameters, in an external cavity diode laser system, we observe second-order phase transition with multiple (three or four) thresholds in the measured power-current-temperature three dimensional phase diagram. Such controlled death and revival of second-order phase transition sheds new insight into the nature of ubiquitous second-order phase transition. Our theory and experiment show that the single threshold second-order phase transition is only a special case of the more general multi-threshold second-order phase transition, which is an even richer phenomenon.Comment: 5 pages, 3 figure

Quantum Memory Process with a Four-Level Atomic Ensemble

We examine in detail the quantum memory technique for photons in a double $\Lambda$ atomic ensemble in this work. The novel application of the present technique to create two different quantum probe fields as well as entangled states of them is proposed. A larger zero-degeneracy class besides dark-state subspace is investigated and the adiabatic condition is confirmed in the present model. We extend the single-mode quantum memory technique to the case with multi-mode probe fields, and reveal the exact pulse matching phenomenon between two quantized pulses in the present system.Comment: 7 pages, 1 figure, to appear in Euro. Phys. J.

Existence of independent random matching

This paper shows the existence of independent random matching of a large (continuum) population in both static and dynamic systems, which has been popular in the economics and genetics literatures. We construct a joint agent-probability space, and randomized mutation, partial matching and match-induced type-changing functions that satisfy appropriate independence conditions. The proofs are achieved via nonstandard analysis. The proof for the dynamic setting relies on a new Fubini-type theorem for an infinite product of Loeb transition probabilities, based on which a continuum of independent Markov chains is derived from random mutation, random partial matching and random type changing.Comment: Published at http://dx.doi.org/10.1214/105051606000000673 in the Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute of Mathematical Statistics (http://www.imstat.org

Incomplete quantum state estimation: a comprehensive study

We present a detailed account of quantum state estimation by joint maximization of the likelihood and the entropy. After establishing the algorithms for both perfect and imperfect measurements, we apply the procedure to data from simulated and actual experiments. We demonstrate that the realistic situation of incomplete data from imperfect measurements can be handled successfully.Comment: 11 pages, 10 figure

Nernst Effect and Superconducting Fluctuations in Zn-doped YBa2_{2}Cu3_{3}O7−δ_{7-\delta}

We report the measurements of in-plane resistivity, Hall effect, and Nernst effect in Zn doped YBa$_{2}$Cu$_{3}$O$_{7-\delta}$ epitaxial thin films grown by pulsed laser deposition technique. The pseudogap temperature, $T^*$, determined from the temperature dependence of resistivity, does not change significantly with Zn doping. Meanwhile the onset temperature ($T^{\nu}$) of anomalous Nernst signal above $T_{c0}$, which is interpreted as evidence for vortex-like excitations, decreases sharply as the superconducting transition temperature $T_{c0}$ does. A significant decrease in the maximum of vortex Nernst signal in mixed state is also observed, which is consistent with the scenario that Zn impurities cause a decrease in the superfluid density and therefore suppress the superconductivity. The phase diagram of $T^*$, $T^{\nu}$, and $T_{c0}$ versus Zn content is presented and discussed.Comment: 6 pages, 5 figures, Latex; v2: to be published in PR

A Worm Algorithm for Two-Dimensional Spin Glasses

A worm algorithm is proposed for the two-dimensional spin glasses. The method is based on a low-temperature expansion of the partition function. The low-temperature configurations of the spin glass on square lattice can be viewed as strings connecting pairs of frustrated plaquettes. The worm algorithm directly manipulates these strings. It is shown that the worm algorithm is as efficient as any other types of cluster or replica-exchange algorithms. The worm algorithm is even more efficient if free boundary conditions are used. We obtain accurate low-temperature specific heat data consistent with a form c = T^{-2} exp(-2J/(k_BT)), where T is temperature and J is coupling constant, for the +/-J two-dimensional spin glass.Comment: 4 pages, 3 figure

Hedging in Field Theory Models of the Term Structure

We use path integrals to calculate hedge parameters and efficacy of hedging in a quantum field theory generalization of the Heath, Jarrow and Morton (HJM) term structure model which parsimoniously describes the evolution of imperfectly correlated forward rates. We also calculate, within the model specification, the effectiveness of hedging over finite periods of time. We use empirical estimates for the parameters of the model to show that a low dimensional hedge portfolio is quite effective.Comment: 18 figures, Invited Talk, International Econophysics Conference, Bali, 28-31 August 200