(Color online) Wigner functions of the conditional states under imperfect experimental conditions. Here, we set reasonable values for the preparation efficiency of the initial bi-photon state: η ∣ 2 〉 = 0.8 , and the detection efficiency of single-photon detector: η SPD = 0.5 . The quantum states are calculated with various squeezed parameters: (a) β = 0 , (b) β = 0.005 , (c) β = 0.01 , (d) β = 0.05 . The inset is the Wigner function in the plane of X = 0 .