Journal of Statistical Physics, Vol. 110, Nos. 3–6, March 2003, p. 957-970.
We present a new short-time approximation scheme for evaluation of decoher-ence. At low temperatures, the approximation is argued to apply at intermediate times as well. It then provides a tractable approach complementary to Markovian-type approximations, and appropriate for evaluation of deviations from pure states in quantum computing models.