Atomic Comagnetometer with a Closed-Loop Optically Aligned 87 Rb Dual-Frequency Oscillator

Abstract

Comagnetometers have been widely used in fundamental research, such as tests of spin-gravity coupling and searches for permanent electric dipole moments (EDMs). Here, we report a comagnetometer that consists of simultaneous closed-loop oscillation of the $F=1$ and $F=2$ hyperfine Zeeman transitions of optically aligned ${}^{87}$$\mathrm{Rb}$ atoms. The Allan deviation of the $F=2$ and $F=1$ oscillation-frequency ratio reaches $1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$ after running continuously for 2 days, corresponding to a sensitivity of approximately $4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}19}\phantom{\rule{0.2em}{0ex}}\mathrm{eV}$ for the measurement of the hypothetical spin-dependent gravitational energy of the proton. The long-term stability of the comagnetometer can be further improved by system-level thermal control and optimization of the experimental parameters.