Dynamical Processes in Exactly Solvable Quantum Mechanical Systems I. : General Physics

概要

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Decoherence and relaxation processes in quantum systems are studied on the basis of an exactly solvable model. That is, a generalized Coleman-Hepp model is analyzed in a framework of a spin coherent state representation which enables us to determine time evolution of the whole system as successive applications of rotation operators. A density matrix of the whole system and reduced density matrices of constituent subsystems are obtained to yield quasi-probability densities and averages of observable of an incident particle and a detector (reservoir) system. Numerical evaluation of these quantities is performed to find decoherence like phenomena for larger values of N (a number of detector spins) and S_l (magnitude of a detector spin). An appearance of a mixed state (i.e., vanishing of off-diagonal elements of a reduced matrix) is explicitly shown when N and/or S_l become infinity. Namely, this occurs in the thermodynamic limit (N→∞) and/or in the classical apparatus limit (S_l→∞).
社団法人日本物理学会の論文
2000-01-15