Appearance and disappearance of quantum correlations in measurement-based feedback control of a mechanical oscillator

Understand

Quantum correlations between imprecision and back-action are a hallmark of continuous linear measurements.

• Here we study how measurement-based feedback can be used to improve the visibility of quantum correlations due to the interaction of a laser field with a nano-optomechanical system.
• Back-action imparted by the meter laser, due to radiation pressure quantum fluctuations, gives rise to correlations between its phase and amplitude quadratures.
• These quantum correlations are observed in the experiment both as squeezing of the meter field fluctuations below the vacuum level in a homodyne measurement, and as sideband asymmetry in a heterodyne measurement, demonstrating the common origin of both phenomena.