Interferometry using a multi-photon tunneling coupler

Summary form only given. Interferometers involving special quantum states can show fascinating and counter-intuitive effects. While the general principles governing these effects have been understood for some time, the recent discussion of photon DeBroglie waves has provided an interesting and useful perspective. The basic idea is that whenever photons display correlated dynamics as they pass through a nonlinear interferometer, a description in terms of multi-photon bound particles can be useful. Multi-photon particles behave quite differently from uncorrelated photons: a bound collection of N photons has total momentum N/spl planck/k. Interference of such particles has fringe period /spl lambda//N. This runs against our intuition for linear optics, although some implementations are intuitive. For example, if a system includes up-conversion, then /spl lambda//2 photons are produced, and the presence of interference at this wavelength is quite natural. Naturally, loss will impose limitations on this kind of coherent manipulation, and must be carefully studied. The Kerr coupler was proposed as a potential implementation of the above interferometer. The Kerr effect can provide a "binding force" holding a packet of photons together as it passes through the coupler. A number of issues must be addressed in any realistic design-including loss and temporal pulse shape. Here we study the basic effect using a simplified two-mode model.