Linear amplifiers and attenuators
H. Fearn · Quantum Optics Journal of the European Optical Society Part B · 1990
Unitary operators are used to derive an input-output theory for idealised inverted population amplifiers and attenuators. The method is a modification of a field theoretic technique of thermofields. Arbitrarily long chains of amplifier plus attenuator sections are conveniently treated using the modified thermofield approach, including the useful case of squeezed internal modes, where various new results have been obtained.