Letter | Published:

Sideband cooling beyond the quantum backaction limit with squeezed light

Nature volume 541, pages 191195 (12 January 2017) | Download Citation

Abstract

Quantum fluctuations of the electromagnetic vacuum produce measurable physical effects such as Casimir forces and the Lamb shift1. They also impose an observable limit—known as the quantum backaction limit—on the lowest temperatures that can be reached using conventional laser cooling techniques2,3. As laser cooling experiments continue to bring massive mechanical systems to unprecedentedly low temperatures4,5, this seemingly fundamental limit is increasingly important in the laboratory6. Fortunately, vacuum fluctuations are not immutable and can be ‘squeezed’, reducing amplitude fluctuations at the expense of phase fluctuations. Here we propose and experimentally demonstrate that squeezed light can be used to cool the motion of a macroscopic mechanical object below the quantum backaction limit. We first cool a microwave cavity optomechanical system using a coherent state of light to within 15 per cent of this limit. We then cool the system to more than two decibels below the quantum backaction limit using a squeezed microwave field generated by a Josephson parametric amplifier. From heterodyne spectroscopy of the mechanical sidebands, we measure a minimum thermal occupancy of 0.19 ± 0.01 phonons. With our technique, even low-frequency mechanical oscillators can in principle be cooled arbitrarily close to the motional ground state, enabling the exploration of quantum physics in larger, more massive systems.

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Acknowledgements

This work was financially supported by NIST and the DARPA QuASAR program. J.B.C. acknowledges the NIST National Research Council Postdoctoral Research Associateship Program for its financial support. Contribution of the US government, not subject to copyright.

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Affiliations

  1. National Institute of Standards and Technology, Boulder, Colorado 80305, USA

    • Jeremy B. Clark
    • , Florent Lecocq
    • , Raymond W. Simmonds
    • , José Aumentado
    •  & John D. Teufel

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Contributions

J.B.C. and J.D.T. conceived and designed the experiment. F.L. fabricated the optomechanical circuit and contributed technical input for the experimental set-up. J.B.C. performed the measurements and data analysis, and developed the theory with assistance from J.D.T. All authors contributed to writing the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to John D. Teufel.

Reviewer Information Nature thanks P. Tombesi and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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DOI

https://doi.org/10.1038/nature20604

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