Spatiotemporal few-photon optical nonlinearities through linear optics and measurement

Abstract

It is well known that optical nonlinearities are extremely weak at the quantum, or single-photon, level. This has been one of the major difficulties for optical implementations of universal, scalable quantum computation. Knill, Laflamme, and Milburn [Nature (London) 409, 46 (2001)] showed, among other things, that one could perform the elusive two-qubit logic gates with only linear-optical elements if one also uses extra single photons and measurement. In this work, we apply linear-optics techniques to produce effects in few-photon beams that are more familiar to strong-field nonlinear optics. Specifically, we show that these methods are sufficient to change the spatial (or temporal) properties of a light beam with strong dependence on its constituent number of photons; such phenomena cannot occur via linear optics alone.