  It has been shown that perfect photon absorption can occur in the linear
excitation regime of cavity quantum electrodynamics (CQED), in which photons
from two identical light fields coupled into two ends of the cavity are
completely absorbed and result in excitation of the polariton state of the CQED
system. The output light from the cavity is totally suppressed by the
destructive interference and the polariton state can only decay incoherently
back to the ground state. Here we analyze the perfect photon absorption and
onset of optical bistability in the nonlinear regime of the CQED and show that
the perfect photon absorption persists in the nonlinear regime of the CQED
below the threshold of the optical bistability. Therefore the perfect photon
absorption is a phenomenon that can be observed in both linear and nonlinear
regimes of CQED. Furthermore, our study reveals for the first time that the
optical bistability is influenced by the input-light interference and can be
manipulated by varying the relative phase of the two input fields.
