Demonstration of the spatial separation of the entangled quantum   side-bands of an optical field
  Quantum optics experiments on "bright" beams typically probe correlations between side-band modes. However the extra degree of freedom represented by this dual mode picture is generally ignored. We demonstrate the experimental operation of a device which can be used to separate the quantum side-bands of an optical field. We use this device to explicitly demonstrate the quantum entanglement between the side-bands of a squeezed beam. 
E. H. Huntington, G. N. Milford, C. Robilliard, T. C. Ralph, O.   Gloeckl, U. L. Andersen, S. Lorenz and G. Leuchs