Indistinguishability of photonic qubits emitted from trapped ${}^{40}$Ca${}^{+}$ ions via pulsed excitation

We investigate the indistinguishability of Raman photons generated from two trapped ${}^{40}$Ca${}^{+}$ ions using few-nanosecond excitation pulses. We elucidate how spontaneous scattering back to the initial state affects Hong-Ou-Mandel interference. We identify the mean number of back-decays as a measurable single-emitter quantity that correlates with achievable interference visibility of photons from two identical emitters.