Progress towards a dual-isotope trapped mercury ion atomic clock: Further studies of background gas collision shifts

As part of an on-going effort to build a dual-isotope ion trap clock based on the ¹⁹⁹Hg⁺ and ²⁰¹Hg⁺ ground state hyperfine transitions, we continue to characterize the systematic sensitivities of the ²⁰¹Hg⁺ 29.9GHz clock transition. Here we present an extension to the previous ²⁰¹Hg⁺ collision shift measurement for helium[1] to other background gases. We also measured the collision shifts in the ¹⁹⁹Hg⁺ 40.5GHz clock transition in the same physical system. We find that frequency sensitivities to collisions with background gas for the two isotopes agree within a factor of two. We will also discuss planned collision shift measurements with co-trapped ¹⁹⁹Hg⁺ and ²⁰¹Hg⁺, as an important step towards a dual-isotope atomic clock.