Pulsed excitation and shelving schemes for ¹³⁸Ba⁺ ion-photon entanglement generation

The scaling of trapped ions in a single ion trap zone is hampered by spectral crowding, the increased susceptibility to background gas collisions, and complicated optical addressing setups. To avoid these problems, we envision connecting smaller trapped-ion quantum computers through optical links of single photons, allowing for quantum entanglement of separated ion chains. We use ¹³⁸Ba⁺ as a communication ion because it has a relatively long-wavelength S_1/2 to P_1/2 transition and is therefore the most amenable to integrated photonic technologies. The main limitation in this solution is the entanglement generation rate, which previously was limited by optical pumping to the D_3/2 state, so our goal is to increase this rate by exciting directly from the S state. We present details about a new single-photon generation scheme using a pulsed laser source at 493 nm for the S to P transition in ¹³⁸Ba⁺ and an electron-shelving detection scheme using the narrow 1762 nm transition from S_1/2 to D_5/2.