Consider a regime where we consider a [Mach-Zehnder interferometer](Mach-Zehnder%20interferometer.md) where single photons are sent to its inputs.  #QuantumMechanics/QuantumOptics #Electromagnetism/Optics #PhysicalExamples/PhysicalExamplesInQuantumMechanics/PhysicalExamplesInQuantumOptics