Abstract
We study time evolution of a subsystem's density matrix under unitary evolution, generated by a sufficiently complex, say quantum chaotic, Hamiltonian, modeled by a random matrix. We exactly calculate all coherences, purity and fluctuations. We show numerically that the reduced density matrix can be described in terms of a noncentral correlated Wishart ensemble for which we are able to perform analytical calculations of the eigenvalue density. Our description accounts for a transition from an arbitrary initial state toward a random state at large times, enabling us to determine the convergence time after which random states are reached. We identify and describe a number of other interesting features, such as a series of collisions between the largest eigenvalue and the bulk, accompanied by a phase transition in its distribution function.
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More From: Journal of Physics A: Mathematical and Theoretical
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