A simple formula relating the input and output quantum states of a beamsplitter is derived and applied to the analysis of an interferometer with a photon duplicator along one arm. The result is in direct contrast with the case in which a linear amplifier is employed in place of the photon duplicator. © 1986.
Yuen, H. P. (1986). Quantum amplication and the detection of empty de Broglie waves. Physics Letters A, 113(8), 401–404. https://doi.org/10.1016/0375-9601(86)90659-6