F -state quenching with CH4 for buffer-gas cooled 171Y b+ frequency standard

Abstract

We report that methane, CH4, can be used as an efficient F-state quenching gas for trapped ytterbium ions. The quenching rate coefficient is measured to be (2.8 ± 0.3) × 106 s-1 Torr-1. For applications that use microwave hyperfine transitions of the ground-state 171Y b ions, the CH4 induced frequency shift coefficient and the decoherence rate coefficient are measured as δν/ν = (-3.6 ± 0.1) × 10-6 Torr-1 and 1/T2 = (1.5 ± 0.2) × 105 s-1 Torr-1. In our buffer-gas cooled 171Y b+ microwave clock system, we find that only ≤10-8 Torr of CH4 is required under normal operating conditions to efficiently clear the F-state and maintain ≥85% of trapped ions in the ground state with insignificant pressure shift and collisional decoherence of the clock resonance.