Triggered indistinguishable single photons with narrow line widths from site-controlled quantum dots.

In this Letter, we present narrow line width (7 μeV), nearly background-free single-photon emission (g(2)(0) = 0.02) and highly indistinguishable photons (V = 0.73) from site-controlled In(Ga)As/GaAs quantum dots. These excellent properties have been achieved by combining overgrowth on ex situ pit-patterned substrates with vertical stacking of spectrally distinct quantum dot layers. Our study paves the way for large-scale integration of quantum dots into quantum photonic circuits as indistinguishable single-photon sources.