The radium ion's metastable 6d2D5/2 and 6d2D3/2 state lifetimes

The radium ion is a clock candidate for high precision and transportable optical clocks. We measured the lifetimes of the radium ion's metastable 6d2D5/2 and 6d2D3/2 states. The D5/2 state is a common choice for optical clocks with alkaline earth ions. For 225Ra+, with the advantage of large hyperfine splittings, the D3/2 state can be used to build an optical clock with only two IR wavelengths (828 and 1079 nm), which makes it an intriguing option for a transportable clock based on integrated photonics. Experimentally measured lifetimes provide a better understanding of these potential clock states and assist in the analysis of future radium optical clocks. The lifetime measurements also benchmarked the coupled-cluster single-double triple (CCSDT) technique that was used to independently calculate the lifetimes. CCSDT was designed to calculate heavy elements properties.  The agreement supports the theoretical approach so that other challenging radioactive elements may be pursued in experiments with confidence.