Phase-coherent detection of an optical dipole force by Doppler velocimetry

TL;DR

This paper demonstrates phase-coherent Doppler detection of optical dipole forces in large ion crystals, enabling precise characterization of motional modes with phase and frequency information, advancing ion trap quantum control.

Contribution

The authors introduce a phase-coherent Doppler velocimetry technique for optical dipole force detection in ion crystals, providing access to phase information not available in traditional methods.

Findings

Successful measurement of COM motional mode oscillations

Agreement between experimental results and harmonic oscillator model

Enhanced discrimination of nearly degenerate motional modes

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 $^{9}$Be$^{+}$ 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.