45,609 research outputs found
The gravitational field of a global monopole
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 the Entangled states L\times N\times N
We presented a general classification scheme for the tripartite 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 system is given.Comment: 21 pages; published in Phys. Rev.
Maximal violation of Clauser-Horne-Shimony-Holt inequality for four-level systems
Clauser-Horne-Shimony-Holt inequality for bipartite systems of 4-dimension is
studied in detail by employing the unbiased eight-port beam splitters
measurements. The uniform formulae for the maximum and minimum values of this
inequality for such measurements are obtained. Based on these formulae, we show
that an optimal non-maximally entangled state is about 6% more resistant to
noise than the maximally entangled one. We also give the optimal state and the
optimal angles which are important for experimental realization.Comment: 7 pages, three table
Generation of a High-Visibility Four-Photon Entangled State and Realization of a Four-Party Quantum Communication Complexity Scenario
We obtain a four-photon polarization-entangled state with a visibility as
high as (95.35\pm 0.45)% directly from a single down-conversion source. A
success probability of (81.54\pm 1.38)% is observed by applying this entangled
state to realize a four-party quantum communication complexity scenario (QCCS),
which comfortably surpass the classical limit of 50%. As a comparison, two
Einstein-Podolsky-Rosen (EPR) pairs are shown to implement the scenario with a
success probability of (73.89\pm 1.33)%. This four-photon state can be used to
fulfill decoherence-free quantum information processing and other advanced
quantum communication schemes.Comment: REVTEX 4.0, 4 pages, 4 figures, 1 tabl
Quantum state transmission in a cavity array via two-photon exchange
The dynamical behavior of a coupled cavity array is investigated when each
cavity contains a three-level atom. For the uniform and staggered intercavity
hopping, the whole system Hamiltonian can be analytically diagonalized in the
subspace of single-atom excitation. The quantum state transfer along the
cavities is analyzed in detail for distinct regimes of parameters, and some
interesting phenomena including binary transmission, selective localization of
the excitation population are revealed. We demonstrate that the uniform
coupling is more suitable for the quantum state transfer. It is shown that the
initial state of polariton located in the first cavity is crucial to the
transmission fidelity, and the local entanglement depresses the state transfer
probability. Exploiting the metastable state, the distance of the quantum state
transfer can be much longer than that of Jaynes-Cummings-Hubbard model. A
higher transmission probability and longer distance can be achieved by
employing a class of initial encodings and final decodings.Comment: 8 pages, 7 figures. to appear in Phys. Rev.
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