Let a random pure state vector be chosen in nk‐dimensional Hilbert space, and consider an n‐dimensional subsystem’s density matrix P. P will usually be close to the totally unpolarized mixed state if k is large. Specifically, the rms deviation of a probability from the mean value 1/n is [(1−1/n2)/(kn +1)]1/2. ’’Random’’ refers to unitarily invariant Haar measure.
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Research Article| August 11 2008
Entropy of an n‐system from its correlation with a k‐reservoir
J. Math. Phys. 19, 1028–1031 (1978)
Elihu Lubkin; Entropy of an n‐system from its correlation with a k‐reservoir. J. Math. Phys. 1 May 1978; 19 (5): 1028–1031. https://doi.org/10.1063/1.523763
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