  Probing quantum entanglement with macroscopic objects allows us to test
quantum mechanics in new regimes. One way to realize such behavior is to couple
a macroscopic mechanical oscillator to a continuous light field via radiation
pressure. In view of this, the system that is discussed comprises an
optomechanical cavity driven by a coherent optical field in the unresolved
sideband regime where we assume Gaussian states and dynamics. We develop a
framework to quantify the amount of entanglement in the system numerically.
Different from previous work, we treat non-Markovian noise and take into
account both the continuous optical field and the cavity mode. We apply our
framework to the case of the Advanced Laser Interferometer Gravitational-Wave
Observatory and discuss the parameter regimes where entanglement exists, even
in the presence of quantum and classical noises.
