(color online) Parity operator expectation against phase θ for different mean photon numbers of Fock state n (the mean photon number of coherent state |α|² = 2). (a) The curve of parity operator expectation for different n; (b) the three-dimensional (3D) plot of parity operator expectation against phase θ as n increases; (c) the 3D plot of parity operator expectation against phase θ as n decreases.