  The loss of contrast in double-slit electron-diffraction due to dephasing and
decoherence processes is studied. It is shown that the spatial correlation
function of diffraction patterns can be used to distinguish between dephasing
and decoherence. This establishes a measure of time-reversibility that does not
require the determination of coherence terms of the density matrix, while von
Neumann entropy, another measure of time-reversibility, does require coherence
terms. This technique is exciting in view of the need to understand and control
the detrimental experimental effects of contrast loss and for fundamental
studies on the transition from the classical to the quantum regime.

Quantum Physics