Optical beam splitter, Mach–Zehnder interferometer and the delayed choice issue

Abstract John Wheeler's delayed choice thought experiment is often invoked in discussions of the wave-particle duality of quantum physics. Every so often interpretations are offered that do not restrict to straight physics. The key element of the 'Gedankenexperiment' is a Mach–Zehnder interferometer composed of two optical beam splitters. The quantum description of these devices and the treatment of delayed choice experiment in the framework of quantum optics are discussed here.