Single-photon interference due to motion in an atomic collective   excitation
  We experimentally demonstrate the generation of heralded bi-chromatic single photons from an atomic collective spin excitation (CSE). The photon arrival times display collective quantum beats, a novel interference effect resulting from the relative motion of atoms in the CSE. A combination of velocity-selective excitation with strong laser dressing and the addition of a magnetic field allows for exquisite control of this collective beat phenomenon. The present experiment uses a diamond scheme with near-IR photons that can be extended to include telecommunications-wavelengths or modified to allow storage and retrieval in an inverted-Y scheme. 
Daniel J. Whiting, Nikola Sibalic, James Keaveney, Charles S. Adams   and Ifan G. Hughes
physics.atom-ph physics.optics quant-ph