Background-free quantum frequency conversion of single photons from a   semiconductor quantum dot
  We demonstrate background-free quantum frequency conversion of single photons from an epitaxially-grown InAs quantum dot. Single photons at \approx 980 nm are combined with a pump laser near 1550 nm inside a periodically-poled lithium niobate (PPLN) waveguide, generating single photons at \approx 600 nm. The large red-detuning between the pump and signal wavelengths ensures nearly background-free conversion, avoiding processes such as upconversion of anti-Stokes Raman scattered pump photons in the PPLN crystal. Second-order correlation measurements on the single photon stream are performed both before and after conversion, confirming the preservation of photon statistics during the frequency conversion process. 
Serkan Ates, Imad Agha, Antonio Badolato, Kartik Srinivasan
quant-ph cond-mat.mes-hall physics.optics