Collisional decoherence of molecular wavepackets at ultracold temperatures

We present an analysis of collisional decoherence of molecular superposition states in an ultracold gas. The approach is based on the derivation of a linear differential equation for the time evolution of the reduced density matrix for molecular rotational states. The tetradic decoherence operator is expressed in terms of collision $T$ matrix elements and the decoherence rate is obtained from eigenvalues of this operator. We consider collisional decoherence of rotational wavepackets in a bath of ultracold atoms and decoherence due to identical molecule -- molecule scattering.