Phonon counting and intensity interferometry of a nanomechanical resonator


In optics, the ability to measure individual quanta of light (photons) enables a great many applications, ranging from dynamic imaging within living organisms1 to secure quantum communication2. Pioneering photon counting experiments, such as the intensity interferometry performed by Hanbury Brown and Twiss3 to measure the angular width of visible stars, have played a critical role in our understanding of the full quantum nature of light4. As with matter at the atomic scale, the laws of quantum mechanics also govern the properties of macroscopic mechanical objects, providing fundamental quantum limits to the sensitivity of mechanical sensors and transducers. Current research in cavity optomechanics seeks to use light to explore the quantum properties of mechanical systems ranging in size from kilogram-mass mirrors to nanoscale membranes5, as well as to develop technologies for precision sensing6 and quantum information processing7,8. Here we use an optical probe and single-photon detection to study the acoustic emission and absorption processes in a silicon nanomechanical resonator, and perform a measurement similar to that used by Hanbury Brown and Twiss to measure correlations in the emitted phonons as the resonator undergoes a parametric instability formally equivalent to that of a laser9. Owing to the cavity-enhanced coupling of light with mechanical motion, this effective phonon counting technique has a noise equivalent phonon sensitivity of 0.89 ± 0.05. With straightforward improvements to this method, a variety of quantum state engineering tasks using mesoscopic mechanical resonators would be enabled10, including the generation and heralding of single-phonon Fock states11 and the quantum entanglement of remote mechanical elements12,13.

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Figure 1: Phonon counting and device characterization.
Figure 2: Phonon counting sensitivity.
Figure 3: Phonon lasing.
Figure 4: Phonon intensity correlations.


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We thank F. Marquardt and A. G. Krause for discussions, and V. B. Verma, R. P. Miriam and S. W. Nam for their help with the single-photon detectors used in this work. This work was supported by the DARPA ORCHID and MESO programmes, the Institute for Quantum Information and Matter, an NSF Physics Frontiers Center with the support of the Gordon and Betty Moore Foundation, and the Kavli Nanoscience Institute at Caltech. Part of the research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. A.H.S.-N. acknowledges support from NSERC. S.G. was supported by a Marie Curie International Out-going Fellowship within the 7th European Community Framework Programme.

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O.P., S.M.M., J.D.C., S.G. and A.H.S.-N. planned the experiment. J.D.C., S.G., G.S.M., S.M.M. and A.H.S.-N. performed the device design and fabrication. F.M. and M.D.S. provided the single-photon detectors along with technical support for their installation and running. J.D.C., S.M.M., G.S.M. and O.P. performed the measurements, analysed the data and wrote 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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Cohen, J., Meenehan, S., MacCabe, G. et al. Phonon counting and intensity interferometry of a nanomechanical resonator. Nature 520, 522–525 (2015).

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