Input-Output Theory

Abstract

In the early 1980’s calculations were performed on the degree of squeezing that could be achieved within cavity parametric amplifiers. These calculations indicated that the field inside the cavity could be squeezed by no more than a factor of two under steady state conditions [1]. As a result lore spread that cavities were bad for squeezing. It turns out, however, that because of a remarkable interference effect between the field that is reflected off of the input port mirror, and the field that — after entering the cavity — is squeezed and then re-emitted, the field external to the cavity can exhibit arbitrarily large amounts of squeezing: even though the field inside the cavity only exhibits a factor of two squeezing [2]. How to calculate the quantum statistical properties of the field exiting a cavity given the input field and the internal field had become an important issue that needed to be solved for the advancement of the squeezed state field. Works by Yurke and Denker [3], Yurke [4], and Collett and Gardner [5–7] were instrumental in showing the way. This is, in part, what input-output theory is about.