| Summary: | 碩士 === 國立成功大學 === 物理學系碩博士班 === 94 === We mainly study a quantum Brownian motion from an exact solvable model which describes the interaction between a harmonic oscillator and an one-dimensional massless scalar field. Apart from the effect of classical stochastic processes, we are more interested in the decoherence arising from the decay of the off-diagonal elements of the reduced density matrix for the system, and we shall point out that the time scale of the decoherence is shorter than that of the dissipation. Additionally, we will derive the exact master equation to investigate the time-dependent behavior of the reduced density matrix, and show the different features between various systems (for example, a harmonic oscillator , and a free particle). Finally, we compare the exact master equation with the one in the Markovian approximation.
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