Production of optical phase space vortices with non-locally distributed   mode converters
  Optical vortices have been observed in a wide variety of optical systems. They can be observed directly in the wavefront of optical beams, or in the correlations between pairs of entangled photons. We present a novel optical vortex which appears in a non-local plane of the two-photon phase space, composed of a single degree of freedom of each photon of an entangled pair. The preparation of this vortex can be viewed as a "non-local" or distributed mode converter. We show how these novel optical vortices of arbitrary order can be prepared in the spatial degrees of freedom of entangled photons. 
R. M. Gomes, A. Salles, F. Toscano, P. H. Souto Ribeiro and S. P.   Walborn
quant-ph physics.optics