OPERATIONAL APPROACH TO THE PHASE OF A QUANTUM-FIELD - COMMENT

Interpretational difficulties of a quantum measurement [J.W Noh, A. Fougeres, and L. Mandel, Phys. Rev. A 45, 424 (1992)] are pointed out. The nonunitaxity of the respective exponential phase operator reflects an enhanced noise, which can be reduced by discarding ambiguous output data. Consequently, dispersion of such measurements does not represent a meaningful performance measure relevant to the input state. Moreover, the proposed model of quantum phase measurements provides a discrete spectrum of the quantum phase operator, whereas the phase-shift parameter is continuous.