Single Pairs of Time-bin Entangled Photons
Time-bin-entangled photons are ideal for long-distance quantum communication via optical ﬁbers, since time-bin entanglement is not susceptible to fluctuations in the polarization of the photons. We built the first source where, even at high creation rates, each excitation pulse generates at most one time-bin-entangled pair. Our source is based on a site-controlled quantum dot, which generates single polarization-entangled photon pairs. These pairs are then converted, without loss of entanglement strength, into single time-bin-entangled photon pairs. These single pairs of time-bin entangled photons can be used for secure and accurate quantum communication.