All-Optical Switching Demonstration using Two-Photon Absorption and the   Classical Zeno Effect
  Low-contrast all-optical Zeno switching has been demonstrated in a silicon nitride microdisk resonator coupled to a hot atomic vapor. The device is based on the suppression of the field build-up within a microcavity due to non-degenerate two-photon absorption. This experiment used one beam in a resonator and one in free-space due to limitations related to device physics. These results suggest that a similar scheme with both beams resonant in the cavity would correspond to input power levels near 20 nW. 
S. M. Hendrickson, C. N. Weiler, R. M. Camacho, P. T. Rakich, A. I.   Young, M. J. Shaw, T. B. Pittman, J. D. Franson and B....
quant-ph physics.optics