  Long distance quantum communication is one of the prime goals in the field of
quantum information science. With information encoded in the quantum state of
photons, existing telecommunication fiber networks can be effectively used as a
transport medium. To achieve this goal, a source of robust entangled single
photon pairs is required. While time-bin entanglement offers the required
robustness, currently used parametric down-conversion sources have limited
performance due to multi-pair contributions. We report the realization of a
source of single time-bin entangled photon pairs utilizing the
biexciton-exciton cascade in a III/V self-assembled quantum dot. We analyzed
the generated photon pairs by an inherently phase-stable interferometry
technique, facilitating uninterrupted long integration times. We confirmed the
entanglement by performing a quantum state tomography of the emitted photons,
which yielded a fidelity of 0.69(3) and a concurrence of 0.41(6).
