January 23rd 2001 Tuesday, 15:00 p.m.

Stochastic Description of Open Quantum Systems

Enric Verdaguer

(Universidad de Barcelona)

An open quantum system is modeled by a harmonic oscillator coupled linearly to an infinite set of independent harmonic oscillators with a general spectral density. Objects such as the Feynman and Vernon influence functional, the reduced density matrix, the Wigner function, the master equation and the Langevin equation are often used to describe open quantum systems. We briefly review them and discuss their interrelations. We show that a formal Langevin equation can be derived to decribe the quantum properties of the system even beyond the semiclassical regime. The reduced Wigner function for the system turns out to be exactly the formal distribution function resulting from averaging both over the initial conditions and the stochastic source of the Langevin equation. This provides an alternative road for the computation of the master equation. We also show that the quantum correlation functions for the system can be deduced within the stochastic description. In particular, when the system is not Markovian more information can be extracted from the Langevin equation than from the master equation.

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Last modified: Tue Jan 16 17:04:52 CET 2001