  The ability to trap and to manipulate individual atoms is at the heart of
current implementations of quantum simulations, quantum computing, and
long-distance quantum communication. Controlling the motion of larger particles
opens up yet new avenues for quantum science, both for the study of fundamental
quantum phenomena in the context of matter wave interference, and for new
sensing and transduction applications in the context of quantum optomechanics.
Specifically, it has been suggested that cavity cooling of a single
nanoparticle in high vacuum allows for the generation of quantum states of
motion in a room-temperature environment as well as for unprecedented force
sensitivity. Here, we take the first steps into this regime. We demonstrate
cavity cooling of an optically levitated nanoparticle consisting of
approximately 10e9 atoms. The particle is trapped at modest vacuum levels of a
few millibar in the standing-wave field of an optical cavity and is cooled
through coherent scattering into the modes of the same cavity. We estimate that
our cooling rates are sufficient for ground-state cooling, provided that
optical trapping at a vacuum level of 10e-7 millibar can be realized in the
future, e.g., by employing additional active-feedback schemes to stabilize the
optical trap in three dimensions. This paves the way for a new light-matter
interface enabling room-temperature quantum experiments with mesoscopic
mechanical systems.
