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SU(N) x S_{m}Invariant Eigenspaces of N^{m} x N^{m} Mean Density Matrices  Paul B. Slater
;  Date: 
26 Jun 1998  Subject:  quantph  Affiliation:  University of California  Abstract:  We extend to additional probability measures and scenarios, certain of the recent results of Krattenthaler and Slater (quantph/9612043), whose original motivation was to obtain quantum analogs of seminal work on universal data compression of Clarke and Barron. KS obtained explicit formulas for the eigenvalues and eigenvectors of the 2^m x 2^m density matrices derived by averaging the mfold tensor products with themselves of the 2 x 2 density matrices. The weighting was done with respect to a oneparameter (u) family of probability distributions, all the members of which are sphericallysymmetric (SU(2)invariant) over the ``Bloch sphere’’ of twolevel quantum systems. For u = 1/2, one obtains the normalized volume element of the minimal monotone (Bures) metric. In this paper, analyses parallel to those of KS are conducted, based on an alternative "natural" measure on the density matrices recently proposed by Zyczkowski, Horodecki, Sanpera, and Lewenstein (quantph/9804024). The approaches of KS and that based on ZHSL are found to yield [1 + m/2] identical SU(2) x S_{m}invariant eigenspaces (but not coincident eigenvalues for m > 3). Companion results, based on the SU(3) form of the ZHSL measure, are obtained for the twofold and threefold tensor products of the 3 x 3 density matrices. We find a rather remarkable limiting procedure (selection rule) for recovering from these analyses, the (permutationallysymmetrized) multiplets of SU(3) constructed from two or three particles. We also analyze the scenarios (all for m = 2) N = 2 x 3, N= 2 x 3 x 2, N= 3 x 2 x 2 and N = 4 and, in addition, generalize the ZHSL measure, so that it incorporates a family of (symmetric) Dirichlet distributions (rather than simply the uniform distribution), defined on the (N1)dimensional simplex of eigenvalues.  Source:  arXiv, quantph/9806089  Services:  Forum  Review  PDF  Favorites 


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