  We present the concept of nonreciprocal interferometers. These two-way
devices let particles pass in both directions, but in one direction break the
phase of the particles' wave functions. Such filters can be realized by using,
for example, asymmetric quantum rings. Furthermore, we propose arrangements of
these interferometers to obtain larger interferometers which are expected to
exhibit a puzzling behavior that resembles Maxwell demon action. We indicate an
opportunity to resolve this puzzle experimentally.
