Quantum decoherence in the entanglement entropy of a composite particle and its relationship to coarse graining in the Husimi function

Abstract

I investigate quantum decoherence in a one-body density matrix of a composite particle consisting of two correlated particles. Because of the two-body correlation in the composite particle, quantum decoherence occurs in the one-body density matrix that has been reduced from the twobody density matrix. As the delocalization of the distribution of the composite particle grows, the entanglement entropy increases, and the system can be well described by a semi-classical approximation, wherein the center position of the composite particle can be regarded as a classical coordinate. I connect the quantum decoherence in the one-body density matrix of a composite particle to the coarse graining in a phase space distribution function of a single particle and associate it with the Husimi function.