Indistinguishability of single photons from dissimilar single-photon sources

In quantum mechanics, particles in identical states are indistinguishable, giving rise to effects with no classical analog. For instance, the bosonic nature of light insures that upon interference two indistinguishable photons will coalesce into a single inseparable state. Through this coalescence, we demonstrate that photons produced from two separate quantum dots are indistinguishable. Further, we show that single photons created in a fundamentally different process - parametric down-conversion in a nonlinear crystal - can be manipulated to be indistinguishable from those from quantum dots. The quantum interference in both experiments occurs with a visibility reduced from unity because the quantum dot photons are not lifetime-limited due to the presence of pure dephasing. The measured visibility closely matches the theoretical visibility predicted for photons with the parameters of those measured here.