QUANTUM INSTABILITIES AND DECOHERENCE PROBLEM

A decoherence problem is discussed by means of quantum continuous meas urement theory. It is shown that the conditional state of quantum syst em interacting with a bath preserves its initial purity. In this prese ntation decoherence arises as a result of averaging over the stochasti c times of reduction moments (''clicks''). A method based on external phase feedback is proposed to slow down the decoherence of field super position state in an open optical cavity. It is also shown that an ato m placed inside the optical cavity plays a role of internal self-organ ized positive feedback between field and atom, which leads to an expon ential increase in the mean dipole moment of the atom for the field in itially prepared in a superposition of coherent states, i.e. to quantu m instability.