Single atom-scale diamond defect allows a large Aharonov-Casher phase

We propose an experiment that would produce and measure a large Aharonov-Casher (AC) phase in a solid-state system under macroscopic motion. A diamond crystal is mounted on a spinning disk in the presence of a uniform electric field. Internal magnetic states of a single nitrogen-vacancy $\left(\text{N-}V\right)$ defect, replacing interferometer trajectories, are coherently controlled by microwave pulses. The AC phase shift is manifested as a relative phase, of up to 17 radians, between components of a superposition of magnetic substates, which is two orders of magnitude larger than that measured in any other atom-scale quantum system.

Figure 1

(Color online) Proposed experimental setup. (a) Geometry of experiment; a diamond crystal on a spinning disk between two charged plates with a uniform static magnetic field in the $z$ direction. (b) Energy level diagram of the $\text{N-}V$ center.

Figure 2

(Color online) (a) Pulse scheme (pulse times not to scale) and rotating-frame Bloch sphere state evolution for a single rotation of the disk, with $\pi$ rad of accumulated AC phase. Runs with multiple rotations would have further $\pi$ pulses whenever the diamond passes points A and B. (b) Example fluorescence signal as a function of electric field strength, where the maximum AC phase is 10 rad. $y$ axis units are arbitrary. Dots represent example experimental data points.