Entanglement Generation by Fock-State Filtration
K. J. Resch, Jeremy L. O’Brien, Till J. Weinhold, Kaoru Sanaka, B. P. Lanyon, Nathan K. Langford, Andrew G. White · Physical Review Letters · 2007
We demonstrate a Fock-state filter which is capable of preferentially blocking single photons over photon pairs. The large conditional nonlinearities are based on higher-order quantum interference, using linear optics, an ancilla photon, and measurement. We demonstrate that the filter acts coherently by using it to convert unentangled photon pairs to a path-entangled state. We quantify the degree of entanglement by transforming the path information to polarization information; applying quantum state tomography we measure a tangle of T=(20+/-9)%.