  In this work, we investigate a tool for hybrid quantum systems that
implements a transducer to map small position changes of a micro-mechanical
membrane onto the polarization of a laser beam. This is achieved with an
interferometric setup that has reduced needs for stabilization. Specifically,
an oscillating silicon nitride membrane placed in the middle of an asymmetric
optical cavity causes phase shifts in the reflected, near-resonant light field.
A beam displacer is used to combine the signal beam with a mode-matched,
orthogonally polarized reference beam for polarization encoding. Subsequent
balanced homodyne measurement is used to detect thermal membrane noise. Minor
improvements in the design should achieve sufficiently high signal-to-noise
ratio for the detection of motional quantum noise in the regime of high
opto-mechanical coupling strength. This setup can provide a robust quantum link
between a micro-mechanical oscillator and other systems such as atomic
ensembles.
