Condensed Matter Physics, 2000, vol. 3, No. 1(21), p. 51-73, English

Author(s): A.K.Chattah (Centro Atomico Bariloche, Av. E. Bustillo Km 9.5, CP 8400, Bariloche, Argentina), M.O.Caceres (Centro Atomico Bariloche and Instituto Balseiro, CNEA and Universidad Nacional de Cuyo, Av. E. Bustillo Km 9.5, CP 8400, Bariloche, Argentina)

Using Terwiel's cumulants the Markovian approximation to arrive to the Quantum Master Equation, for a system interacting with a thermal bath, is revisited. The second order weak coupling approximation is analyzed, then a Kossakowski-Lindblad form for the generator is written in terms of the position and momentum operators. A weak coupling approximation for the stochastic non-Markovian wave function is worked out. A free particle model interacting with a thermal quantum bath is studied in the context of Schr\"{o}dinger-Langevin picture. A phenomenological point of view is introduced in order to overcome certain difficulties in the time evolution -- in the second order approximation -- for the free particle Hamiltonian.

Comments: Figs. 0, Refs. 31, Tabs. 0.

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