title: Complex Squeezing and Force Measurement Beyond the Standard Quantum Limit.
abstract: A continuous quantum field, such as a propagating beam of light, may be characterized by a squeezing spectrum that is inhomogeneous in frequency. We point out that homodyne detectors, which are commonly employed to detect quantum squeezing, are blind to squeezing spectra in which the correlation between amplitude and phase fluctuations is complex. We find theoretically that such complex squeezing is a component of ponderomotive squeezing of light through cavity optomechanics. We propose a detection scheme called synodyne detection, which reveals complex squeezing and allows the accounting of measurement backaction. Even with the optomechanical system subject to continuous measurement, such detection allows the measurement of one component of an external force with sensitivity only limited by the mechanical oscillator's thermal occupation.
authors.affiliation: Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK 8000 Aarhus C, Denmark.|Department of Physics, University of California, Berkeley, California 94720, USA.
authors.forename: L F
authors.initials: LF
authors.lastname: Buchmann
authors.affiliation: Department of Physics, University of California, Berkeley, California 94720, USA.
authors.forename: S
authors.initials: S
authors.lastname: Schreppler
authors.affiliation: Department of Physics, University of California, Berkeley, California 94720, USA.
authors.forename: J
authors.initials: J
authors.lastname: Kohler
authors.affiliation: Department of Physics, University of California, Berkeley, California 94720, USA.|Fachbereich Physik, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany.
authors.forename: N
authors.initials: N
authors.lastname: Spethmann
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: D M
authors.initials: DM
authors.lastname: Stamper-Kurn