Measurement induced focussing of radiation from independent single   photon sources
  We present a technique based on multi-photon detection which leads to a strong focussing of photons scattered by independent single photon emitters. For N single photon sources it is shown that if m - 1 photons are detected in a particular direction (with m \leq N) the probability to detect the m-th photon in the same direction can be as high as 100%. This measurement induced focussing effect is already clearly visible for m>2. 
R. Wiegner, S. Oppel, J. von Zanthier and G. S. Agarwal
quant-ph