  Quadrature squeezing of light is investigated in a hybrid atom-optomechanical
system comprising a cloud of two-level atoms and a movable mirror mediated by a
single-mode cavity field. When the system is at high temperatures with
quadrature fluctuations of light much above the standard quantum limit (SQL),
excitation counting on the collective atomic state can effectively reduce the
light noise close to the SQL. When the system is at low temperatures,
considerable squeezing of light below the SQL is found at steady state. The
squeezing is enhanced by simply increasing the atom-light coupling strength
with the laser power optimized close to the unstable regime, and further noise
reduction is achieved by decreasing various losses in the system. The presence
of atoms and excitation counting on the atoms lessen the limitation of thermal
noise, and the squeezing can be achieved at environment temperature of the
order K. The nonclassicality of the light, embodied by the negative
distributions of the Wigner function, is also studied by making non-Gaussian
measurements on the atoms. It is shown that with feasible parameters excitation
counting on the atoms is effective in inducing strongly optical
nonclassicality.
