  Time-bin entangled photons are ideal for long-distance quantum communication
via optical fibers. Here we present a source where, even at high creation
rates, each excitation pulse generates at most one time-bin entangled pair.
This is important for the accuracy and security of quantum communication. Our
site-controlled quantum dot generates single polarization-entangled photon
pairs, which are then converted, without loss of entanglement strength, into
single time-bin entangled photon pairs.
