title: Optical detection of the quantization of collective atomic motion.
abstract: We directly measure the quantized collective motion of a gas of thousands of ultracold atoms, coupled to light in a high-finesse optical cavity. We detect strong asymmetries, as high as 3:1, in the intensity of light scattered into low- and high-energy motional sidebands. Owing to high cavity-atom cooperativity, the optical output of the cavity contains a spectroscopic record of the energy exchanged between light and motion, directly quantifying the heat deposited by a quantum position measurement's backaction. Such backaction selectively causes the phonon occupation of the observed collective modes to increase with the measurement rate. These results, in addition to providing a method for calibrating the motion of low-occupation mechanical systems, offer new possibilities for investigating collective modes of degenerate gases and for diagnosing optomechanical measurement backaction.
authors.affiliation: Department of Physics, University of California, Berkeley, California 94720, USA. nbrahms@berkeley.edu
authors.forename: Nathan
authors.initials: N
authors.lastname: Brahms
authors.forename: Thierry
authors.initials: T
authors.lastname: Botter
authors.forename: Sydney
authors.initials: S
authors.lastname: Schreppler
authors.forename: Daniel W C
authors.initials: DW
authors.lastname: Brooks
authors.forename: Dan M
authors.initials: DM
authors.lastname: Stamper-Kurn