Measurement-based quantum control of mechanical motion

Massimiliano Rossi, David Mason, Junxin Chen, Yeghishe Tsaturyan, Albert Schliesser

Published 2018-05-14Version 1

Feedback cooling is a ubiquitous control protocol to suppress thermal motion of mechanical systems, by applying a compensating force based on a displacement measurement record. Once the measurement is so strong that its inevitable quantum backaction dominates the mechanical fluctuations, it enters the domain of quantum control, allowing one to prepare and stabilize a quantum-mechanically pure motional state. We implement this protocol in a "bad-cavity" optomechanical system based on an ultracoherent (Q = 10^9) soft-clamped nanomechanical membrane resonator. The near-ideal measurement is strong and efficient; it operates both at the Heisenberg measurement-disturbance uncertainty limit and the standard quantum limit (SQL) to within 35%. Feedback-cooling the resonator to its quantum ground state (n = 0.29 +- 0.03) realizes a long-standing goal in the field, and adds motion to the degrees of freedom amenable to measurement-based quantum control techniques.