Zeeman decoherence effect of trapped ¹⁹⁹Hg⁺ ion Ramsey spectra

In the ¹⁹⁹Hg⁺ ion microwave clock, the Zeeman decoherence effect caused by the overlapping of Zeeman sidebands and the radial secular motion sidebands will decrease the contrast of the Ramsey fringe, thus reducing the signal-to-noise ratio of the spectra. In this paper, the Zeeman decoherence effect is analyzed theoretically and investigated experimentally. A simplified model is built to describe the Ramsey spectral probability, in which the transverse relaxation time T₂ is introduced to characterize the influence of the Zeeman decoherence effect phenomenologically. The experiments were carried out on a linear quadrupole trap ¹⁹⁹Hg⁺ ion clock. The results show that the probability model matches well with the experimental data, and the magnetic field value should be more than 150 mGs (1 Gs = 10⁻⁴ T) to avoid the Zeeman decoherence effect.