Creating single time-bin entangled photon pairs

When a single emitter is excited by two phase-coherent pulses with a time delay, each of the pulses can lead to the emission of a photon pair, thus creating a ``time-bin entangled'' state. Double pair emission can be avoided by initially preparing the emitter in a metastable state. We show how photons from separate emissions can be made indistinguishable, permitting their use for multi-photon interference. Possible realizations with single atoms or ions and with quantum dots are discussed. The method might also allow the direct creation of {\$}n{\$}-photon entangled states (n$>$2).