We report on two-photon interference of highly indistinguishable single photons emitted by a quantum dot. Strictly resonant excitation with picosecond laser pulses has been used to prepare coherent states with a significantly increased coherence time $(T_2\sim 1\text{ns})$ and reduced lifetime $(T_1\sim 650\text{ps})$, as compared to a nonresonant excitation scheme. Indistinguishable photons, with visibilities greater than 70%, have been observed by measuring the Hong-Ou-Mandel dip without postselection of the interfering photons. Near-unity indistinguishable photons should be achievable by preventing fluctuations in the electrostatic environment in the vicinity of the dots, considered as an important source of decoherence.

• Received 31 March 2014
• Revised 20 June 2014

DOI:https://doi.org/10.1103/PhysRevB.90.041303