Experimental demonstration of optimal unambiguous state discrimination - art. no. 040305

We present a full demonstration of unambiguous state discrimination between nonorthogonal quantum states. Using a free-space interferometer we have re alized the optimum quantum measurement scheme for two nonorthogonal states of light, known as the Ivanovic-Dieks-Peres (IDP) measurement. We have gain ed access to all three possible outcomes of this measurement. All aspects o f this generalized measurement scheme, including its superiority over a sta ndard von Neumann measurement, have been demonstrated within 1.5% of the ID P predictions.