title: Phase-coherent detection of an optical dipole force by Doppler velocimetry.
abstract: We report phase-coherent Doppler detection of optical dipole forces using large ion crystals in a Penning trap. The technique is based on laser Doppler velocimetry using a cycling transition in 9Be+ near 313 nm and the center-of-mass (COM) ion motional mode. The optical dipole force is tuned to excite the COM mode, and measurements of photon arrival times synchronized with the excitation potential show oscillations with a period commensurate with the COM motional frequency. Experimental results compare well with a quantitative model for a driven harmonic oscillator. This technique permits characterization of motional modes in ion crystals; the measurement of both frequency and phase information relative to the driving force is a key enabling capability--comparable to lockin detection - providing access to a parameter that is typically not available in time-averaged measurements. This additional information facilitates discrimination of nearly degenerate motional modes.
authors.affiliation: National Institute of Standards and Technology, Ion Storage Group, Boulder, CO 80305, USA. michael.biercuk@sydney.edu.au
authors.forename: M J
authors.initials: MJ
authors.lastname: Biercuk
authors.forename: H
authors.initials: H
authors.lastname: Uys
authors.forename: J W
authors.initials: JW
authors.lastname: Britton
authors.forename: A P
authors.initials: AP
authors.lastname: Vandevender
authors.forename: J J
authors.initials: JJ
authors.lastname: Bollinger