Superposition States and Interference Effects in Quantum Optics

5 Superposition States and Interference Effects in Quantum Optics 

We have omitted the coefficient for reflection at mirrors Ml and M2 since this has a 

Two-photon quantum interference sometimes is ascribed to local interference of the photons at the beamsplitter. However, Kwiat et al. [43] and Pittman et al. [44] demonstrated experimentally that the critical factor is the whether the wave-functions are distinguishable at the detectors. The photons do not need to be at the beamsplitter simultaneously. 

Linearly polarized light provides another instructive illustration of superposition states in quantum optics. As discussed in Sect. 3.3, unpolarized light can be viewed as a mixture of photons with all possible linear polarizations. Light that is polarized at an angle 6 with respect to an arbitrary vertical axis can be viewed as a coherent superposition of vertically and horizontally polarized light with coefficients Cy=cos(0) and Ch = sin(0)  

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