Decoherence-fluctuation relation and measurement noise

We discuss fluctuations in the measurement process and how these fluctuatio ns are related to the dissipational parameter characterizing quantum dampin g or decoherence. On the example of the measuring current of the variable-b arrier or QPC problem we discuss the extra noise or fluctuation connected w ith the different possible outcomes of a measurement. This noise has an enh anced short time component which could be interpreted as due to "telegraph noise" or "wavefunction collapses". Furthermore, the parameter giving the s trength of this component is related to the parameter giving the rate of da mping or decoherence. (C) 1999 Elsevier Science B.V. All rights reserved.