  We study photon blockade and anti-bunching in the cavity of an optomechanical
system in which the mechanical resonator is coupled to a two-level system
(TLS). In particular, we analyze the effects of the coupling strength (to the
mechanical mode), transition frequency, and decay rate of TLS on the photon
blockade. The statistical properties of the cavity field are affected by the
TLS, because the TLS changes the energy-level structure of the optomechanical
system via dressed states formed by the TLS and the mechanical resonator. We
find that the photon blockade and tunneling can be significantly changed by the
transition frequency of the TLS and the coupling strength between the TLS and
the mechanical resonator. Therefore, our study provides a method to tune the
photon blockade and tunneling using a controllable TLS.
