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Null Weak Values and Quantum State Discrimination


  Oded Zilberberg [1]  ,  Alessandro Romito [2]  ,  David J. Starling [3,4]  ,  Gregory A. Howland [3]  ,  Curtis J. Broadbent [3,5]  ,  John C. Howell [1,3]  ,  Yuval Gefen [1]  
 [1] Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 76100, Israel
[2] Dahlem Center for Complex Quantum Systems and Fachbereich Physik, Freie Universitaet Berlin, 14195 Berlin, Germany
[3] Department of Physics and Astronomy, University of Rochester, Rochester, New York 14627, USA.
[4] Division of Science, Pennsylvania State University, Hazleton, Pennsylvania 18202, USA.
[5] Rochester Theory Center, University of Rochester, Rochester, New York 14627, USA.

We present a measurement protocol for discriminating between two di fferent quantum states of a qubit with high fidelity. The protocol is comprised of a projective measurement performed on the system with small probability (a.k.a. weak partial-collapse), followed by a tuned postselection. We report on an optical experimental implementation of the scheme. We show that our protocol leads to an ampli ed signal-to-noise ratio (as compared with a straightforward strong measurement) when discerning between the two quantum states.