37,066 research outputs found
Group theoretical study of LOCC-detection of maximally entangled state using hypothesis testing
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
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
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
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
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
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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