Thursday, June 27, 2013

1306.6301 (H. Mäkelä et al.)

Effects of the rotating wave and secular approximations on

H. Mäkelä, M. Möttönen
We study the effect of the rotating-wave approximation (RWA) and the secular approximation (SA) on the non-Markovianity of an open quantum system consisting of a two-level system interacting with a bosonic zero-temperature reservoir. Using a recently proposed measure for non-Markovianity, we find that the rapidly oscillating terms neglected in the RWA and SA are responsible for the overwhelming majority of the observed non-Markovianity. This can be explained by comparing the time scales during which different terms in the master equation contribute to non-Markovian dynamics. The presence of the rapidly oscillating terms enables us to obtain an approximate analytical expression for the non-Markovianity measure without solving the exact dynamics of the system. With the help of this expression, we show that there is a steep decrease in non-Markovianity for certain values of the parameters of the spectral density. We consider Lorentzian and Ohmic spectral densities as examples.
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