Purification of Single Photons by Temporal Heralding of Quantum Dot Sources

Efficient, high rate photon sources with high single-photon purity are essential ingredients for quantum technologies. Single-photon sources based on solid state emitters such as quantum dots are very advantageous for integrated photonic circuits, but they can suffer from a high two-photon emission probability, which in cases of noncryogenic environment cannot be spectrally filtered. Here we propose two temporal purification-by-heralding methods for using a two-photon emission process to yield highly pure and efficient single-photon emission, bypassing the inherent problem of spectrally overlapping biphoton emission at elevated temperatures. We experimentally emulate their feasibility on the emission from a single nanocrystal quantum dot at room temperature, exhibiting single-photon purities exceeding 99.5%, without a significant loss of single-photon efficiency. By utilizing these methods with commercially available components, nanocrystal quantum dots can be made realistic high-quality room-temperature sources for single photons. These approaches can also be applied for any indeterministic source of spectrally broadband photon pairs.