  Coherent wave splitting is crucial in interferometers. Normally, the waves
after this splitting are of the same type. But recent progress in interaction
between atom and light has led to the coherent conversion of photon to atomic
excitation. This makes it possible to split an incoming light wave into a
coherent superposition state of atom and light and paves the way for an
interferometer made of different types of waves. Here we report on a Rabi-like
coherent-superposition oscillation observed between atom and light and a
coherent mixing of light wave with excited atomic spin wave in a Raman process.
We construct a new kind of hybrid interferometer based on the atom-light
coherent superposition state. Interference fringes are observed in both optical
output intensity and atomic output in terms of the atomic spin wave strength
when we scan either or both of the optical and atomic phases. Such a hybrid
interferometer can be used to interrogate atomic states by optical detection
and will find its applications in precision measurement and quantum control of
atoms and light.
