Trapped Barium Ion Laser Cooling Outside the Steady State

In this poster we present a method for pulsed laser cooling of Ba⁺¹³⁸ ions which can increase qubit state detection rate and improve the cooling limits. Singly charged Barium ions have a lambda-type system such that the Doppler cooling and qubit state detection cycle between three states 6S_1/2, 6P_1/2, and 5D_3/2. When the ion is driven with two resonant fields, the ion population can be driven into a coherent dark state that is a superposition of the 6S_1/2 state and 5D_3/2 state that have opposite phase and equal amplitude. If this happens, the ion will not fluoresce and cannot be cooled. This is typically fixed by the laser polarization modulation or by introducing a magnetic field, but these solutions have limitations. We propose a scheme in which the two resonant laser fields are applied as short interleaving pulses to break this dark state and increase the ion’s average probability of being in the fluorescing 6P1/2 state through this non-steady state evolution.