  The effect of time-varying electromagnetic fields on electron coherence is
investigated. A sinusoidal electromagnetic field produces a time varying
Aharonov-Bohm phase. In a measurement of the interference pattern which
averages over this phase, the effect is a loss of contrast. This is effectively
a form of decoherence. We calculate the magnitude of this effect for various
electromagnetic field configurations. The result seems to be sufficiently large
to be observable.
