  High contrast matter-wave interferometry is essential in various fundamental
quantum mechanical experiments as well as for technical applications. Thereby,
contrast and sensitivity are typically reduced by decoherence and dephasing
effects. While decoherence accounts for a general loss of quantum information
in a system due to entanglement with the environment, dephasing is due to
collective time-dependent external phase shifts, which can be related to
temperature drifts, mechanical vibrations or electromagnetic oscillations. In
contrast to decoherence, dephasing can in principle be reversed. Here, we
demonstrate in experiment and theory a method for the analysis and reduction of
the influence of dephasing noise and perturbations consisting of several
external frequencies in an electron interferometer. This technique uses the
high spatial and temporal resolution of a delay line detector to reveal and
remove dephasing perturbations by second order correlation analysis. It allows
matter-wave experiments under perturbingly lab conditions and can be applied in
principle to electron, atom, ion, neutron and molecule interferometers.
