Experimental realization of a measurement conditional unitary operation   at single photon level and application to detector characterization
  Our last experimental results on the realization of a measurement-conditional unitary operation at single photon level are presented. This gate operates by rotating by $90^o$ the polarization of a photon produced by means of Type-II Parametric Down Conversion conditional to a polarization measurement on the correlated photon. We then propose a new scheme for measuring the quantum efficiency of a single photon detection apparatus by using this set-up. We present experimental results obtained with this scheme compared with {\it traditional} biphoton calibration. Our results show the interesting potentiality of the suggested scheme. 
M. Genovese, G. Brida, M. Chekhova, M.Gramegna, L. Krivitsky, S.   Kulik, M.L.Rastello