A new trapped ion clock based on 201HG+

There are two stable odd isotopes of mercury with singly ionized hyperfine structure suitable for a microwave clock: ¹⁹⁹Hg⁺ and ²⁰¹Hg⁺. Virtually all trapped mercury ion clocks to date have used the 199 isotope. We have begun to investigate the viability of a trapped ion clock based on ²⁰¹Hg⁺. We have measured the unperturbed frequency of the ²S_1/2 F = 1, m_F = 0 to ²S_1/2 F = 2, m_F =0 clock transition to be 29.9543658211(2) GHz. In this paper we describe initial measurements with ²⁰¹Hg⁺ and new applications to clocks and fundamental physics.