STOCHASTIC WAVE-FUNCTION METHOD VERSUS DENSITY-MATRIX - A NUMERICAL COMPARISON

Numerical investigations of open quantum systems, which are widely per formed in such fields as photochemistry, quantum optics and nuclear ma gnetic resonance, can, in the Markovian regime, be based either on the master equation for the reduced density operator or on a stochastic p rocess in the Hilbert space of the reduced system. It is shown that th e CPU time consumptions of the two methods depend on the system size N as Nalpha+1 and as R(N)N-alpha, respectively. The exponent alpha is c haracteristic of the specific system. R(N) is the number of process re alizations generated in the simulation and is defined by prescribing t he tolerable statistical error of the result. Since R(N) is a non-incr easing function of N, the stochastic method is found to be always fast er for large systems. This is demonstrated for the example of the diss ipative Morse oscillator excited by an intense short laser pulse. (C) 1997 Elsevier Science B.V.