441,999 research outputs found

    Controlled generation of field squeezing with cold atomic clouds coupled to a superconducting transmission line resonator

    Full text link
    We propose an efficient method for controlled generation of field squeezing with cold atomic clouds trapped close to a superconducting transmission line resonator. It is shown that, based on the coherent strong magnetic coupling between the collective atomic spins and microwave fields in the transmission line resonator, two-mode or single mode field squeezed states can be generated through coherent control on the dynamics of the system. The degree of squeezing and preparing time can be directly controlled through tuning the external classical fields. This protocol may offer a promising platform for implementing scalable on-chip quantum information processing with continuous variables.Comment: accepted by Phys. Rev.

    The gravitational field of a global monopole

    Full text link
    We present an exact solution to the non-linear equation which describes a global monopole in the flat space. We re-examine the metric and the geodesics outside the global monopole. We will see that a global monopole produces a repulsive gravitational field outside the core in addition to a solid angular deficit. The lensing property of the global monopole and the global monopole-antimonopole annihilation mechanism are studied.Comment: 8 pages, no figure

    Classification of Arbitrary Multipartite Entangled States under Local Unitary Equivalence

    Full text link
    We propose a practical method for finding the canonical forms of arbitrary dimensional multipartite entangled states, either pure or mixed. By extending the technique developed in one of our recent works, the canonical forms for the mixed NN-partite entangled states are constructed where they have inherited local unitary symmetries from their corresponding N+1N+1 pure state counterparts. A systematic scheme to express the local symmetries of the canonical form is also presented, which provides a feasible way of verifying the local unitary equivalence for two multipartite entangled states.Comment: 22 pages; published in J. Phys. A: Math. Theo

    Entangling two atoms in spatially separated cavities through both photon emission and absorption processes

    Get PDF
    We consider a system consisting of a Λ\Lambda-type atom and a V-type atom, which are individually trapped in two spatially separated cavities that are connected by an optical fibre. We show that an extremely entangled state of the two atoms can be deterministically generated through both photon emission of the Λ\Lambda-type atom and photon absorption of the V-type atom in an ideal situation. The influence of various decoherence processes such as spontaneous emission and photon loss on the fidelity of the entangled state is also investigated. We find that the effect of photon leakage out of the fibre on the fidelity can be greatly diminished in some special cases. As regards the effect of spontaneous emission and photon loss from the cavities, we find that the present scheme with a fidelity higher than 0.98 may be realized under current experiment conditions.Comment: 12 pages, 4 figure

    Spreading Speed, Traveling Waves, and Minimal Domain Size in\ud Impulsive Reaction-diffusion Models

    Get PDF
    How growth, mortality, and dispersal in a species affect the species’ spread and persistence constitutes a central problem in spatial ecology. We propose impulsive reaction-diffusion equation models for species with distinct reproductive and dispersal stages. These models can describe a seasonal birth pulse plus nonlinear mortality and dispersal throughout the year. Alternatively they can describe seasonal harvesting, plus nonlinear birth and mortality as well as dispersal throughout the year. The population dynamics in the seasonal pulse is described by a discrete map that gives the density of the populationat the end stage as a possibly nonmonotone function of the density of the population at the beginning of the stage. The dynamics in the dispersal stage is governed by a nonlinear reaction-diffusion equation in a bounded or unbounded domain. We develop a spatially explicit theoretical framework that links species vital rates (mortality or fecundity) and dispersal characteristics with species’ spreading speeds, traveling wave speeds, as well as and minimal domain size for species persistence. We provide an explicit formula for the spreading speed in terms of model parameters, and show that the spreading speed can be characterized as the slowest speed of a class of traveling wave solutions. We also determine an explicit formula for the minimal domain size using model parameters. Our results show how the diffusion coefficient, and the combination of discrete- and continuous-time growth and mortality determine the spread and persistence dynamics of the population in a wide variety of ecological scenarios. Numerical simulations are presented to demonstrate the theoretical results

    Correlations of chaotic eigenfunctions: a semiclassical analysis

    Full text link
    We derive a semiclassical expression for an energy smoothed autocorrelation function defined on a group of eigenstates of the Schr\"odinger equation. The system we considered is an energy-conserved Hamiltonian system possessing time-invariant symmetry. The energy smoothed autocorrelation function is expressed as a sum of three terms. The first one is analogous to Berry's conjecture, which is a Bessel function of the zeroth order. The second and the third terms are trace formulae made from special trajectories. The second term is found to be direction dependent in the case of spacing averaging, which agrees qualitatively with previous numerical observations in high-lying eigenstates of a chaotic billiard.Comment: Revtex, 13 pages, 1 postscript figur

    An entanglement measure for n-qubits

    Full text link
    Recently, Coffman, Kundu, and Wootters introduced the residual entanglement for three qubits to quantify the three-qubit entanglement in Phys. Rev. A 61, 052306 (2000). In Phys. Rev. A 65, 032304 (2007), we defined the residual entanglement for nn qubits, whose values are between 0 and 1. In this paper, we want to show that the residual entanglement for nn qubits is a natural measure of entanglement by demonstrating the following properties. (1). It is SL-invariant, especially LU-invariant. (2). It is an entanglement monotone. (3). It is invariant under permutations of the qubits. (4). It vanishes or is multiplicative for product states.Comment: 16 pages, no figure

    Method for classifying multiqubit states via the rank of the coefficient matrix and its application to four-qubit states

    Full text link
    We construct coefficient matrices of size 2^l by 2^{n-l} associated with pure n-qubit states and prove the invariance of the ranks of the coefficient matrices under stochastic local operations and classical communication (SLOCC). The ranks give rise to a simple way of partitioning pure n-qubit states into inequivalent families and distinguishing degenerate families from one another under SLOCC. Moreover, the classification scheme via the ranks of coefficient matrices can be combined with other schemes to build a more refined classification scheme. To exemplify we classify the nine families of four qubits introduced by Verstraete et al. [Phys. Rev. A 65, 052112 (2002)] further into inequivalent subfamilies via the ranks of coefficient matrices, and as a result, we find 28 genuinely entangled families and all the degenerate classes can be distinguished up to permutations of the four qubits. We also discuss the completeness of the classification of four qubits into nine families

    Classification of the Entangled states L\times N\times N

    Full text link
    We presented a general classification scheme for the tripartite L×N×NL\times N\times N entangled system under stochastic local operation and classical communication. The whole classification procedure consists of two correlated parts: the simultaneous similarity transformation of a commuting matrix pair into a canonical form and the study of internal symmetry of parameters in the canonical form. Based on this scheme, a concrete example of entanglement classification for a 3×N×N3\times N\times N system is given.Comment: 21 pages; published in Phys. Rev.

    Theoretical performance comparison between reference-based coherent BPSK and BCH coded differential BPSK

    Get PDF
    corecore