Anomalous light shift through quantum jumps in quasi-resonant Rayleigh   scattering
  An anomalous light shift in the precession of a ground-state Zeeman coherence is observed: the Larmor frequency increases with the strength of a drive that is blue (red) detuned from a transition out of the lower (upper) energy level. Our measurements are made on Rb 85 atoms traversing an optical cavity containing a few photons; shifts as large as 1% per photon are recorded. The anomalous shift arises from an accumulation of phase driven by quantum jumps. It is stochastic and accompanied by broadening. 
D. G. Norris, A. D. Cimmarusti, L. A. Orozco, P. Barberis-Blostein, H.   J. Carmichael
quant-ph physics.atom-ph