10 [33] U. Leonhardt, Rep. Prog. Phys. 66 , 1207 (2003); J. Skaar, J.C.G. Escartin, and H. Landro, Am. J. Phys. 72 , 1385 (2004). [34] The classical interference fringes, oscillationg like ∼ cos(Δ γ ), are retrieved when the quantum state of the input field is in a coherent state, or when a single pho- ton, in either one of the two beams g 1 or g 2 , undergoes a two-band BO cycle, i.e. for either |Q ( z = 0) 〉 = | 1 〉 1 | 0 〉 2 or |Q ( z = 0) 〉 = | 0 〉 1 | 1 〉 2 .