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  • Open Access

Quantum Correlations of Light from a Room-Temperature Mechanical Oscillator

V. Sudhir, R. Schilling, S. A. Fedorov, H. Schütz, D. J. Wilson, and T. J. Kippenberg*

  • Institute of Physics, École Polytechnique Fédérale de Lausanne, Lausanne 1015, Switzerland

  • *tobias.kippenberg@epfl.ch
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Phys. Rev. X 7, 031055 – Published 26 September, 2017

DOI: https://doi.org/10.1103/PhysRevX.7.031055

Abstract

When an optical field is reflected from a compliant mirror, its intensity and phase become quantum-correlated due to radiation pressure. These correlations form a valuable resource: the mirror may be viewed as an effective Kerr medium generating squeezed states of light, or the correlations may be used to erase backaction from an interferometric measurement of the mirror’s position. To date, optomechanical quantum correlations have been observed in only a handful of cryogenic experiments, owing to the challenge of distilling them from thermomechanical noise. Accessing them at room temperature, however, would significantly extend their practical impact, with applications ranging from gravitational wave detection to chip-scale accelerometry. Here, we observe broadband quantum correlations developed in an optical field due to its interaction with a room-temperature nanomechanical oscillator, taking advantage of its high-cooperativity near-field coupling to an optical microcavity. The correlations manifest as a reduction in the fluctuations of a rotated quadrature of the field, in a frequency window spanning more than an octave below mechanical resonance. This is due to coherent cancellation of the two sources of quantum noise contaminating the measured quadrature—backaction and imprecision. Supplanting the backaction force with an off-resonant test force, we demonstrate the working principle behind a quantum-enhanced “variational” force measurement.

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Popular Summary

In the realm of quantum mechanics, it is impossible to make a measurement (the position of a particle, for example) without influencing the outcome of that measurement—an effect known as measurement-induced backaction. When light is reflected off a mirror to infer its displacement, for example, measurement backaction is due to quantum fluctuations of radiation pressure. Observing the effects of backaction on a macroscopic object under ambient temperature conditions has remained an elusive goal. We observe measurement backaction vis-à-vis the correlations created between the probe light and the motion of a room-temperature mechanical oscillator. We also demonstrate how these quantum correlations can be used to cancel measurement backaction and thus be used to improve the signal-to-noise ratio in force measurements.

Our experimental setup consists of a glass nanostring coupled to a circular optical cavity that supports standing electromagnetic waves around its edge known as “whispering gallery modes.” The system is held in a vacuum chamber at room temperature, and the cavity is probed with a laser. The vibration of the nanostring, acting as an effective nonlinear optical medium, creates correlations between the amplitude and phase of the laser light. We detect these quantum correlations, at the level of 10%, over frequencies of more than an octave around mechanical resonance. In addition, we use these in situ generated correlations to enhance the ability to detect an external force.

This measurement heralds the rise of optomechanical systems as a room-temperature platform for quantum-enhanced metrology and paves the road for the generation of squeezed light inside room-temperature interferometers.

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Phys. Rev. X 7, 031055– Published 26 September, 2017
  • Received 23 May 2017
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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