Measurement-based control of a mechanical oscillator at its thermal decoherence rate

D. J. Wilson, V. Sudhir, N. Piro, R. Schilling, A. Ghadimi, T. J. Kippenberg

Research output: Contribution to journalArticlepeer-review

240 Scopus citations


In real-time quantum feedback protocols1,2, the record of a continuous measurement is used to stabilize a desired quantum state. Recent years have seen successful applications of these protocols in a variety of well-isolated micro-systems, including microwave photons3 and superconducting qubits4. However, stabilizing the quantum state of a tangibly massive object, such as a mechanical oscillator, remains very challenging: the main obstacle is environmental decoherence, which places stringent requirements on the timescale in which the statemust bemeasured. Here we describe a position sensor that is capable of resolving the zero-point motion of a solid-state, 4.3-megahertz nanomechanical oscillator in the timescale of its thermal decoherence, a basic requirement for realtime (Markovian) quantum feedback control tasks, such as groundstate preparation.The sensor is based on evanescent optomechanical coupling to a high-Q microcavity5, and achieves an imprecision four orders of magnitude below that at the standard quantum limit for a weak continuous position measurement6-a 100-fold improvement over previous reports7-9-while maintaining an imprecision-back-action product that is within a factor of five of the Heisenberg uncertainty limit. As a demonstration of its utility, we use the measurement as an error signal with which to feedback cool the oscillator. Using radiation pressure as an actuator, the oscillator is cold damped10 with high efficiency: from a cryogenic-bath temperature of 4.4 kelvin to an effective value of 1.160.1 millikelvin, corresponding to a mean phonon number of 5.360.6 (that is, a ground-state probability of 16 per cent).Our results set a newbenchmark for the performance of a linear position sensor, and signal the emergence of mechanical oscillators as practical subjects for measurement-based quantum control.

Original languageEnglish (US)
Pages (from-to)325-329
Number of pages5
Issue number7565
StatePublished - Aug 20 2015
Externally publishedYes

ASJC Scopus subject areas

  • General


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