LOSS OF COHERENCE IN INTERFEROMETRY

We present a unified treatment of a number of double-slit experiments which give ''which-path'' information. The loss of coherence is described by a random-average model over basis states of the path detector. While the precise physical mechanism depends on the choice of the detector basis, the random-average model shows that the loss of coherence may always be described in terms of a stochastic disturbance to the system due to coupling with the path detector. The possibility of quantum erasers is shown to arise naturally from an appropriate choice of detector basis.