In quantum optics, as in classical optics, beam-splitters play an important role in many experimental settings. Electric elds E1 and E2 enter input ports 1 and 2. For beam splitters with two incoming beams, using a classical, lossless beam splitter with electric fields Ea and Eb each incident at one of the inputs, the two output fields Ec and Ed are linearly related to the inputs through where the 2×2 element is the beam-splitter transfer matrix and r and t. A beam splitter (or beamsplitter, power splitter) is an optical device which can split an incident light beam (e. a laser beam) into two (or sometimes more) beams, which may or may not have the same optical power (radiant flux). Different types of beam splitters exist, as described in the. A symmetric beam-splitter is a cube of glass which reflects half the light that impinges upon it, while allowing the remaining half to pass through unaffected. For our purposes it can simply be viewed as a device that has two input and two output ports, which we label with $mathrm{mid }0⟩$ and. A lossless beam-splitter has certain (complex-valued) probability amplitudes for sending an incoming photon into one of two possible directions. For example, such systems can be interferometers: Michelson-Morley, Mach-Zehnder and Hong-Ou-Mandel [1{4].
