title: Cavity-Assisted Measurement and Coherent Control of Collective Atomic Spin Oscillators.
abstract: We demonstrate continuous measurement and coherent control of the collective spin of an atomic ensemble undergoing Larmor precession in a high-finesse optical cavity. The coupling of the precessing spin to the cavity field yields phenomena similar to those observed in cavity optomechanics, including cavity amplification, damping, and optical spring shifts. These effects arise from autonomous optical feedback onto the atomic spin dynamics, conditioned by the cavity spectrum. We use this feedback to stabilize the spin in either its high- or low-energy state, where, in equilibrium with measurement backaction heating, it achieves a steady-state temperature, indicated by an asymmetry between the Stokes and the anti-Stokes scattering rates. For sufficiently large Larmor frequency, such feedback stabilizes the spin ensemble in a nearly pure quantum state, in spite of continuous measurement by the cavity field.
authors.affiliation: Department of Physics, University of California, Berkeley, California 94720, USA.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Kohler
authors.affiliation: Department of Physics, University of California, Berkeley, California 94720, USA.|Department of Physics and Research Center OPTIMAS, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Spethmann
authors.affiliation: Department of Physics, University of California, Berkeley, California 94720, USA.
authors.forename: Sydney
authors.initials: S
authors.lastname: Schreppler
authors.affiliation: Department of Physics, University of California, Berkeley, California 94720, USA.|Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Dan M
authors.initials: DM
authors.lastname: Stamper-Kurn