A scheme for demonstration of four-photon de Broglie wavelength

We propose a scheme to effectively generate a four-photon path-entangled number state the NOON state i.e. \dfrac1\sqrt2(\vert N,0\rangle+\vert 0,N\rangle) for the demonstration of four-photon de Broglie wavelength. Our scheme requires only linear optical elements, photon detectors and post-selections which are all within the reach of current technology.