  Reflection of a microscopic particle from a mesoscopic/macroscopic `mirror'
generates two-body correlated interference from the incident and reflected
particle substates and their associated mirror substates. The microscopic
momentum exchanged generates two mirror substates which interfere to produce
fringes which do not vanish as the mirror mass increases. The small
displacement between these mirror states can yield negligible environmental
decoherence times. Mirror coherence lengths impose constraints on the extent of
this interference, which are mitigated using interference of the two-body
states associated with the particle reflecting from both of the two surfaces of
a slab of matter in a manner analogous to the classical interference of a pulse
of light reflecting from a `thin film'. This two-body correlated interference
is modeled as a particle traversing a finite well with both the particle and
well treated quantum mechanically. Such a treatment predicts the expected
`thin-film' interference but only as a special case of a more general result.
It is also shown that measurements on only the reflected particle (yielding a
marginal probability density function) can act as a probe to reveal the quantum
state of the macroscopic reflector. For equal masses, coherence of the particle
substate is transferred to the mirror substate, a quantum manifestation of a
familiar classical result.
