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±0.03 phonons along the cavity axis, corresponding to a temperature of 12 μK. We infer a heating rate of Γ_x/2π = 21± 3 kHz, which results in a coherence time of 7.6 μs -- 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/2π = 71 kHz places the system well into the regime of strong cooperativity (C ≈ 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.