Co-existing Xe-129 and Xe-131 masers with active feedback scheme for Xe atomic EDM search*

A permanent electric dipole moment (EDM) of a particle will be induced due to the violation of time reversal invariance, or equivalently the CP-symmetry. A finite EDM would indicate the CP-violation due to new physics beyond the Standard Model (BSM), which is essential in explaining the observed matter excess in the Universe. Improvements in the upper limits on EDMs for diamagnetic atoms should be important in the study of BSM, especially in the hadron sector¹. In order to improve the current experimental upper limit on Xe atomic EDM, 4.1$\times$10^-27 ecm², we are developing a nuclear spin maser with an active feedback scheme, which enables us to observe spin motion avoiding the decay of precession³. We are developing co-existing Xe-129 and Xe-131 spin masers⁴ in order to eliminate the systematic instability in the maser frequency due to the drifts in the magnetic field and in the effective field caused by the Fermi-contact interaction between Xe and polarized Rb. Our recent study suggested that the motion of the Rb spin, which is used to observe the Xe spin precession, is affected by the feedback field for masing. In order to eliminate systematic errors arising from this effect, we developed a time-separated feedback (TSFB) scheme. In this scheme, the observation and the feedback for masing are separated in time. In addition, several efforts are made to improve the signal-to-noise ratio of the measurement which determines the final frequency precision. In this presentation, recent developments and progress of the co-existing Xe-129 and Xe-131 masers with TSFB scheme will be reported.

¹N. Yamanaka et al., Eur. Phys. J. A 53, 54 (2017).
²M. A. Rosenberry and T. E. Chupp, Phys. Rev. Lett. 86, 22 (2001).
³A. Yoshimi et al., Phys. Lett. A 304, 13 (2002).
⁴T. Sato et al., Phys. Lett. A 382, 588-594 (2018).