Generation of maximally entangled photonic states with a quantum-optical Fredkin gate

When a quantum-optical Fredkin gate is embedded into a Mach-Zehnder interferometer, state reduction techniques permit the generation of maximally entangled states of the radiation field when Fock states are input to the device. These exactly reach the Heisenberg limit of phase sensitivity. We investigate the consequences of injecting more general states. and particularly coherent states, into the apparatus, Applications to interferometry and photolithography are discussed.