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Non-classical light generated by quantum-noise-driven cavity optomechanics


Optomechanical systems1, in which light drives and is affected by the motion of a massive object, will comprise a new framework for nonlinear quantum optics, with applications ranging from the storage2,3,4 and transduction5,6 of quantum information to enhanced detection sensitivity in gravitational wave detectors7,8. However, quantum optical effects in optomechanical systems have remained obscure, because their detection requires the object’s motion to be dominated by vacuum fluctuations in the optical radiation pressure; so far, direct observations have been stymied by technical and thermal noise. Here we report an implementation of cavity optomechanics9,10 using ultracold atoms in which the collective atomic motion is dominantly driven by quantum fluctuations in radiation pressure. The back-action of this motion onto the cavity light field produces ponderomotive squeezing11,12. We detect this quantum phenomenon by measuring sub-shot-noise optical squeezing. Furthermore, the system acts as a low-power, high-gain, nonlinear parametric amplifier for optical fluctuations, demonstrating a gain of 20 dB with a pump corresponding to an average of only seven intracavity photons. These findings may pave the way for low-power quantum optical devices, surpassing quantum limits on position and force sensing13,14, and the control and measurement of motion in quantum gases.

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Figure 1: Schematic of cavity and heterodyne detection set-up.
Figure 2: Optomechanical transduction of classical amplitude modulation.
Figure 3: Ponderomotive squeezing and the optomechanical response to quantum radiation pressure fluctuations.


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We acknowledge C. McLeod for assistance with the manuscript. This work was supported by the AFSOR and NSF. T.B. acknowledges support from the FQRNT.

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T.P.P. contributed to the design of the experiment and the development of the theory. All other authors contributed to the design of the experiment, the development of the theory, data acquisition and analysis.

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Correspondence to Daniel W. C. Brooks.

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The authors declare no competing financial interests.

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Supplementary Information

This file contains Supplementary Text and Data, Supplementary Figures 1-7, Supplementary Table 1 and Supplementary References. This file was replaced on 06 September 2012 to correct a missing factor of 1/omega_m in the first relation of equation S4. (PDF 317 kb)

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Brooks, D., Botter, T., Schreppler, S. et al. Non-classical light generated by quantum-noise-driven cavity optomechanics. Nature 488, 476–480 (2012).

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