Motional Quantum Ground State of a Levitated Nanoparticle from Room Temperature

Abstract

We report quantum ground state cooling of a levitated nanoparticle in a room temperature environment. Using coherent scattering into an optical cavity we cool the center of mass motion of a $143$ nm diameter silica particle by more than $7$ orders of magnitude to $n_x=0.43\pm 0.03$ phonons along the cavity axis, corresponding to a temperature of $12\mu$K. We infer a heating rate of ${\Gamma }_x/2\pi =21\pm 3$ kHz, which results in a coherence time of $7.6\mu$s -- or $15$ coherent oscillations -- while the particle is optically trapped at a pressure of $10^{-6}$ mbar. The inferred optomechanical coupling rate of $g_x/2\pi =71$ kHz places the system well into the regime of strong cooperativity ($C\approx 5$). We expect that a combination of ultra-high vacuum with free-fall dynamics will allow to further expand the spatio-temporal coherence of such nanoparticles by several orders of magnitude, thereby opening up new opportunities for macrosopic quantum experiments.

Extended methodology

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