  The second order quantum decoherence (SOQDC)is proposed as a novel
description for the loss of quantum coherence only reflected by second order
quantum correlations. By calculating the two-time correlation function, the
phenomenon of SOQDC is studied in details for a simple model, a two boson
system interacting with a reservoir composed of one or many bosons. The second
order quantum decoherence effects can be observed in the sketched cavity QED
experiment.
