  We propose a theoretical method for enantio-discrimination of chiral
molecules based on a cavity-molecules system, which consists of a cavity
without external driving and an ensemble of chiral mixture (containing left-
and right- handed molecules) confined in the cavity. The molecules in the
chiral mixture are modeled as cyclic three-level models coupled with the
quantized cavity field and two classical light fields. Via the cavity-assisted
three-photon process based on the cyclic three-level model, the intracavity
photons are generated continuously though there is no external driving to the
cavity, and the fields of the photons generated from the the left- and right-
handed molecules differ with the phase difference \pi. This provides a
potential way to detect the enantiomeric excess of chiral mixture by monitoring
the output field of the cavity.
