  Recent experiments have demonstrated the ability to optically cool a
macroscopic mechanical oscillator to its quantum ground state by means of
dynamic backaction. Such experiments allow quantum mechanics to be tested with
mesoscopic objects, and represent an essential step toward quantum optical
memories, transducers, and amplifiers. Most oscillators considered so far are
rigidly connected to their thermal environment, fundamentally limiting their
mechanical Q-factors and requiring cryogenic precooling to liquid helium
temperatures. Here we demonstrate parametric feedback cooling of a
laser-trapped nanoparticle which is entirely isolated from the thermal bath.
The lack of a clamping mechanism provides robust decoupling from internal
vibrations and makes it possible to cool the nanoparticle in all degrees of
freedom by means of a single laser beam. Compared to laser-trapped
microspheres, nanoparticles have the advantage of higher resonance frequencies
and lower recoil heating, which are favorable conditions for quantum ground
state cooling
