Quantum interference indistinguishable photons

Figure 6. a - Schematic of a simplified version of nonlinear sign-shift (NS) operation constructed by a non-polarizing beam splitter of reflectivity II. T i /v) and hour) are the quantum states of input and output photons. The operation is successful when the single-photon detector in ancilla mode 4 counts a single photon, b - The two paths that lead to the detection of exactly one photon in output mode 4. As long as all of the photons are indistinguishable, these two paths can interfere. 

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