36,646 research outputs found

    Group theoretical study of LOCC-detection of maximally entangled state using hypothesis testing

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    In the asymptotic setting, the optimal test for hypotheses testing of the maximally entangled state is derived under several locality conditions for measurements. The optimal test is obtained in several cases with the asymptotic framework as well as the finite-sample framework. In addition, the experimental scheme for the optimal test is presented

    Unitary-process discrimination with error margin

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    We investigate a discrimination scheme between unitary processes. By introducing a margin for the probability of erroneous guess, this scheme interpolates the two standard discrimination schemes: minimum-error and unambiguous discrimination. We present solutions for two cases. One is the case of two unitary processes with general prior probabilities. The other is the case with a group symmetry: the processes comprise a projective representation of a finite group. In the latter case, we found that unambiguous discrimination is a kind of "all or nothing": the maximum success probability is either 0 or 1. We also closely analyze how entanglement with an auxiliary system improves discrimination performance.Comment: 9 pages, 3 figures, presentation improved, typos corrected, final versio

    On the teleparallel limit of Poincare gauge theory

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    We will address the question of the consistency of teleparallel theories in presence of spinning matter which has been a controversial subject of discussion over the last twenty years. We argue that the origin of the problem is not simply the symmetry or asymmetry of the stress-energy tensor of the matter fields, which has been recently analyzed by several authors, but arises at a more fundamental level, namely from the invariance of the field equatins under a frame change, a problem that has been discussed long time ago by Kopczynski in the framework of the teleparallel equivalent of general relativity. More importantly, we show that the problem is not only confined to the purely teleparallel theory but arises actually in every Poincare gauge theory that admits a teleparallel geometry in the absence of spinning sources, i.e. in its classical limit.Comment: 4 pages, RevTe

    Universal approximation of multi-copy states and universal quantum lossless data compression

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    We have proven that there exists a quantum state approximating any multi-copy state universally when we measure the error by means of the normalized relative entropy. While the qubit case was proven by Krattenthaler and Slater (IEEE Trans. IT, 46, 801-819 (2000); quant-ph/9612043), the general case has been open for more than ten years. For a deeper analysis, we have solved the mini-max problem concerning `approximation error' up to the second order. Furthermore, we have applied this result to quantum lossless data compression, and have constructed a universal quantum lossless data compression

    Exponents of quantum fixed-length pure state source coding

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    We derive the optimal exponent of the error probability of the quantum fixed-length pure state source coding in both cases of blind coding and visible coding. The optimal exponent is universally attained by Jozsa et al. (PRL, 81, 1714 (1998))'s universal code. In the direct part, a group representation theoretical type method is essential. In the converse part, Nielsen and Kempe (PRL, 86, 5184 (2001))'s lemma is essential.Comment: LaTeX2e and revetx4 with aps,twocolumn,superscriptaddress,showpacs,pra,amssymb,amsmath. The previous version has a mistak

    The Mixed State of Charge-Density-Wave in a Ring-Shaped Single Crystals

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    Charge-density-wave (CDW) phase transition in a ring-shaped crystals, recently synthesized by Tanda et al. [Nature, 417, 397 (2002)], is studied based on a mean-field-approximation of Ginzburg-Landau free energy. It is shown that in a ring-shaped crystals CDW undergoes frustration due to the curvature (bending) of the ring (geometrical frustration) and, thus, forms a mixed state analogous to what a type-II superconductor forms under a magnetic field. We discuss the nature of the phase transition in the ring-CDW in relation to recent experiments.Comment: 6 pages, 4 figure
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