Buffer gas experiments in mercury (Hg+) ion clock

We report measured buffer gas collision shifts of the 40.507347996xx GHz mercury ion clock transition using inert helium, neon, and argon gases and getterable molecular hydrogen and nitrogen gases. The frequency shift due to methane was also examined. At low partial pressures methane gas did not impact the trapped ion number but was observed to strongly relax the population difference in the two hyperfine clock states thereby reducing the clock resonance signal. A similar population relaxation was also observed for other molecular buffer gases (N₂, H₂) but at much reduced rate.