paper

Phase-coherent sensing of the center-of-mass motion of trapped-ion crystals

arXiv:2008.00035 · doi:10.1103/PhysRevA.102.052609

Abstract

Trapped ions are sensitive detectors of weak forces and electric fields that excite ion motion. Here measurements of the center-of-mass motion of a trapped-ion crystal that are phase-coherent with an applied weak external force are reported. These experiments are conducted far from the trap motional frequency on a two-dimensional trapped-ion crystal of approximately 100 ions, and determine the fundamental measurement imprecision of our protocol free from noise associated with the center-of-mass mode. The driven sinusoidal displacement of the crystal is detected by coupling the ion crystal motion to the internal spin-degree of freedom of the ions using an oscillating spin-dependent optical dipole force. The resulting induced spin-precession is proportional to the displacement amplitude of the crystal, and is measured with near-projection-noise-limited resolution. A pm displacement is detected with a single measurement signal-to-noise ratio of 1, which is an order-of-magnitude improvement over prior phase-incoherent experiments. This displacement amplitude is times smaller than the zero-point fluctuations. With our repetition rate, a pm displacement sensitivity is achieved, which implies yN and Vm sensitivities to forces and electric fields, respectively. This displacement sensitivity, when applied on-resonance with the center-of-mass mode, indicates the possibility of weak force and electric field detection below yN/ion and nV/m, respectively.

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