Narrow Results

We have developed a compensated multi-pole Linear Ion Trap Standard (LITS) that eliminates nearly all frequency sensitivity to residual ion number variations. When operated with ¹⁹⁹Hg⁺, this trapped ion clock has recently demonstrated extremely good stability over a 9-month period. The short-term stability has been measured at 5 × 10^-14/τ^1/2 and an upper limit on long-term fractional frequency deviations of < 2.7 × 10^-17/day was measured in comparison to the laser-cooled primary standards and to the post-processed ultra-stable version of TAI known as TTBIPM using GPS carrier phase time transfer. We have also made a first measurement of the Hg⁺/Hg collision shift and place a limit of +3.8(7.2) × 10^-8/Pa on the shift constant.

In this paper we describe a new clock based on ²⁰¹Hg⁺. All previous mercury ion clocks have been based on ¹⁹⁹Hg⁺. We have recently completed construction of the ²⁰¹Hg⁺ clock and will describe modifications to the design of our existing ¹⁹⁹Hg⁺ clocks to accommodate the new isotope. We will also describe initial spectroscopic measurements of the hyperfine manifold, and possible future experiments. One experiment could place a limit on variations in the strong interaction fundamental constant ratio m_q/Λ_QCD.