913 research outputs found

    The CWKB particle production and classical condensate in de Sitter spacetime

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    The complex time WKB approximation is an effective tool in studying particle production in curved spacetime. We use it in this work to understand the formation of classical condensate in expanding de Sitter spacetime. The CWKB leads to the emergence of thermal spectrum that depends crucially on horizons (as in de Sitter spacetime) or observer dependent horizons (as in Rindler spacetime). A connection is sought between the horizon and the formation of classical condensate. We concentrate on de Sitter spacetime and study the cosmological perturbation of k=0k=0 mode with various values of m/H0m/H_0. We find that for a minimally coupled free scalar field for m2/H02<2m^2/H_0^2<2, the one-mode occupation number grows more than unity soon after the physical wavelength of the mode crosses the Hubble radius and soon after diverges as N(t)O(1)[λphys(t)/H01]2ν21/4N(t)\sim O(1)[\lambda_{phys}(t)/{H_0^{-1}}]^{2\sqrt{\nu^2-1/4}}, where ν(9/4m2/H02)1/2\nu\equiv (9/4 -m^2/{H_0^2})^{1/2}. The results substantiates the previous works in this direction. We also find the correct oscillation and behaviour of N(z)N(z) at small zz from a single expression using CWKB approximation for various values of m/H0m/H_0. We also discuss decoherence in relation to the formation of classical condensate. We also find that the squeezed state formalism and CWKB method give identical results.Comment: 19 pages, revtex, 5 figure

    Multipartite entanglement, quantum-error-correcting codes, and entangling power of quantum evolutions

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    We investigate the average bipartite entanglement, over all possible divisions of a multipartite system, as a useful measure of multipartite entanglement. We expose a connection between such measures and quantum-error-correcting codes by deriving a formula relating the weight distribution of the code to the average entanglement of encoded states. Multipartite entangling power of quantum evolutions is also investigated.Comment: 13 pages, 1 figur

    A new regime of anomalous penetration of relativistically strong laser radiation into an overdense plasma

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    It is shown that penetration of relativistically intense laser light into an overdense plasma, accessible by self-induced transparency, occurs over a finite length only. The penetration length depends crucially on the overdense plasma parameter and increases with increasing incident intensity after exceeding the threshold for self-induced transparency. Exact analytical solutions describing the plasma-field distributions are presented.Comment: 6 pages, 2 figures in 2 separate eps files; submitted to JETP Letter
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