Measurement-based quantum control of mechanical motion

TL;DR

This paper demonstrates measurement-based quantum control of a mechanical resonator's motion, achieving ground-state cooling with high measurement efficiency, advancing quantum control techniques for macroscopic objects.

Contribution

It presents the first implementation of measurement-based quantum control on a millimeter-sized mechanical resonator, including ground-state cooling with near-unity measurement efficiency.

Findings

Resolves zero-point motion with high measurement efficiency

Achieves ground-state cooling below quantum backaction limit

Demonstrates control of macroscopic mechanical motion

Abstract

Controlling a quantum system based on the observation of its dynamics is inevitably complicated by the backaction of the measurement process. Efficient measurements, however, maximize the amount of information gained per disturbance incurred. Real-time feedback then enables both canceling the measurement's backaction and controlling the evolution of the quantum state. While such measurement-based quantum control has been demonstrated in the clean settings of cavity and circuit quantum electrodynamics, its application to motional degrees of freedom has remained elusive. Here we show measurement-based quantum control of the motion of a millimetre-sized membrane resonator. An optomechanical transducer resolves the zero-point motion of the soft-clamped resonator in a fraction of its millisecond coherence time, with an overall measurement efficiency close to unity. We use this position record to feedback-cool a resonator mode to its quantum ground state (residual thermal occupation n = 0.29 +- 0.03), 9 dB below the quantum backaction limit of sideband cooling, and six orders of magnitude below the equilibrium occupation of its thermal environment. This realizes a long-standing goal in the field, and adds position and momentum to the degrees of freedom amenable to measurement-based quantum control, with potential applications in quantum information processing and gravitational wave detectors.