Measurement of the Ba⁺ D_5/2 state lifetime in cryogenic ion trap 

We report measurements of the metastable 5d ²D5/2 state lifetime in ¹³⁸Ba⁺ performed in a cryogenic Paul trap. Such long-lived metastable states are susceptible to lifetime quenching through collisions with background gas and blackbody radiation (BBR), which can contribute to an increased observed decay rate. Typical measurements of long-lived states in room temperature setups require extrapolation to zero temperature and pressure to determine the intrinsic radiative lifetime. Our measurement takes place in a cryogenic environment and minimizes these effects, allowing us to directly study the BBR and collision-induced shift at multiple trap temperatures. We present our measurement approach and discuss systematic studies of temperature-dependent effects.