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Laser cooling of a nanomechanical oscillator into its quantum ground state


The simple mechanical oscillator, canonically consisting of a coupled mass–spring system, is used in a wide variety of sensitive measurements, including the detection of weak forces1 and small masses2. On the one hand, a classical oscillator has a well-defined amplitude of motion; a quantum oscillator, on the other hand, has a lowest-energy state, or ground state, with a finite-amplitude uncertainty corresponding to zero-point motion. On the macroscopic scale of our everyday experience, owing to interactions with its highly fluctuating thermal environment a mechanical oscillator is filled with many energy quanta and its quantum nature is all but hidden. Recently, in experiments performed at temperatures of a few hundredths of a kelvin, engineered nanomechanical resonators coupled to electrical circuits have been measured to be oscillating in their quantum ground state3,4. These experiments, in addition to providing a glimpse into the underlying quantum behaviour of mesoscopic systems consisting of billions of atoms, represent the initial steps towards the use of mechanical devices as tools for quantum metrology5,6 or as a means of coupling hybrid quantum systems7,8,9. Here we report the development of a coupled, nanoscale optical and mechanical resonator10 formed in a silicon microchip, in which radiation pressure from a laser is used to cool the mechanical motion down to its quantum ground state (reaching an average phonon occupancy number of ). This cooling is realized at an environmental temperature of 20 K, roughly one thousand times larger than in previous experiments and paves the way for optical control of mesoscale mechanical oscillators in the quantum regime.

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Figure 1: Optomechanical resonator with phononic shield.
Figure 2: Experimental set-up.
Figure 3: Mechanical and optical response.
Figure 4: Optical cooling results.

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This work was supported by the DARPA/MTO ORCHID program through a grant from the AFOSR, the European Commission (MINOS, QUESSENCE), the European Research Council (ERC QOM), the Austrian Science Fund (CoQuS, FOQUS, START) and the Kavli Nanoscience Institute at the California Institute of Technology. The authors thank B. Baker for help with the cryostat set-up, J.C. thanks R. Li, and J.C. and A.H.S.-N. acknowledge support from NSERC.

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J.C., T.P.M.A. and A.H.S.-N. designed the device, and J.C. fabricated it with support from J.T.H. J.C., T.P.M.A., A.H.S.-N., J.T.H., A.K. and S.G. performed the measurements and analysed the measured data. O.P. and M.A. supervised the measurements and the data analysis. All authors contributed to the writing of the manuscript.

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Correspondence to Oskar Painter.

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The authors declare no competing financial interests.

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Chan, J., Alegre, T., Safavi-Naeini, A. et al. Laser cooling of a nanomechanical oscillator into its quantum ground state. Nature 478, 89–92 (2011).

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