Reversing the temporal envelope of a heralded single photon using a   cavity
  We demonstrate a way to prepare single photons with a temporal envelope that resembles the time reversal of photons from the spontaneous decay process. We use the photon pairs generated from a time-ordered atomic cascade decay: the detection of the first photon of the cascade is used as a herald for the ground-state transition resonant second photon. We show how the interaction of the heralding photon with an asymmetric Fabry-Perot cavity reverses the temporal shape of its twin photon from a decaying to a rising exponential envelope. This single photon is expected to be ideal for interacting with two level systems. 
Bharath Srivathsan, Gurpreet Kaur Gulati, Alessandro Cer\`e, Brenda   Chng, Christian Kurtsiefer
quant-ph