A measurement process is constructed to project an arbitrary two-mode N-photon state to a maximally entangled N-photon state (the {\it NOON}-state). The result of this projection measurement shows a typical interference fringe with an N-photon de Broglie wavelength. For an experimental demonstration, this measurement process is applied to a four-photon superposition state from two perpendicularly oriented type-I parametric down-conversion processes. Generalization to arbitrary N-photon states projection measurement can be easily made and may have wide applications in quantum information. As an example, we formulate it for precision phase measurement.
@article{arxiv.quant-ph/0512212,
title = {Observation of Four-Photon de Broglie Wavelength by State Projection Measurement},
author = {F. W. Sun and B. H. Liu and Y. F. Huang and Z. Y. Ou and G. C. Guo},
journal= {arXiv preprint arXiv:quant-ph/0512212},
year = {2009}
}