Enhanced generation of twin single-photon states via quantum interference in parametric down-conversion: Application to two-photon quantum photolithography

Two-photon interferometric quantum photon lithography for light of wavelength lambda is capable of beating the Rayleigh diffraction limit of resolution lambda/4 to the level of lambda/8. The required twin single-photon states parallel to1>(a)parallel to1>(b), which are converted into maximally entangled states by a 50:50 beam splitter, can be generated from a nondegenerate parametric amplifier initially in vacuum states and with a weak pump field. Increasing the pump strength can slightly increase the production rate of the desired state and it will also increase the production of the twin two-photon states parallel to2>(a)parallel to2>(b), which leads to an unwanted background term. In this paper we show that, assuming a weak pair coherent state as input to the amplifier, quantum interference can be used to quench the production of the parallel to2>(a)parallel to2>(b) state and to enhance the production of the parallel to1>(a)parallel to1>(b) state by almost sixfold.