Stable long-term coupling of a single ion to a cavity mode

With a single trapped calcium ion, strongly localized in an optical resonator, we have realized a cavity-QED system operating under continuous coupling conditions. Ion and field interact via cavity-assisted Raman pulses, applied between the S1/2 ground state and the metastable D3/2 state. We have studied the long-term stability of this interaction at the single- photon level by monitoring the emission from the cavity output and analysing its fluctuations on time-scales up to 10(3) s. The small Allan variances we find confirm that ion and cavity mode are continuously coupled in a deterministically controlled way. Applications include the generation of single photons on demand and an atom - photon interface for optical quantum networks.