Nonclassical two-photon interferometry and lithography with high-gain parametric amplifiers

Optical parametric amplification is a process that leads to the generation of quantum states of light. In the limit of low single-pass gain, this process is often referred to as parametric down conversion, and produces entangled two-photon states. Such states have played a key role in recent studies of quantum optical effects such as quantum teleportation. As the gain of the parametric amplification process is increased, the generated light field still possesses strong quantum correlations, but not of the sort associated with two-photon states. Here we present an analysis of the output state of a parametric amplifier as a function of the single-pass gain, and we find certain signatures of quantum light ~such as the vanishing of the coincidence rate in a Hong-OuMandel interferometer! disappear in the high-gain limit, whereas others ~such as the existence of two-photon interference fringes! remain. Consequently, the intense light field generated by a high-gain parametric amplifier can be utilized in such applications of quantum optics.