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On the volume of the set of mixed entangled states

Karol Zyczkowski·Pawel Horodecki·Anna Sanpera·Maciej Lewenstein
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Abstract

A natural measure in the space of density matrices describing N-dimensional quantum systems is proposed. We study the probability P that a quantum state chosen randomly with respect to the natural measure is not entangled (is separable). We find analytical lower and upper bounds for this quantity. Numerical calculations give P = 0.632 for N=4 and P=0.384 for N=6, and indicate that P decreases exponentially with N. Analysis of a conditional measure of separability under the condition of fixed purity shows a clear dualism between purity and separability: entanglement is typical for pure states, while separability is connected with quantum mixtures. In particular, states of sufficiently low purity are necessarily separable.

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Karol Zyczkowski, Pawel Horodecki, Anna Sanpera, Maciej Lewenstein. 1998-04-09. On the volume of the set of mixed entangled states. https://doi.org/10.1103/physreva.58.883

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