Optica 4, 1052–1058 (2017)

Scientists from the US have now experimentally demonstrated that it is possible to reversibly convert coherence between the polarization and spatial domains. Chukwuemeka Okoro and co-workers from the University of Illinois at Urbana-Champaign and the University of Central Florida have built a coherency converter that transforms two linearly polarized, spatially incoherent fields into two randomly polarized, mutually coherent fields in space. According to the team, the scheme works because the degrees of freedom associated with coherence are effectively classically entangled, akin to entangled multipartite states in quantum mechanics. As a result, coherence can be treated as a resource that can be reversibly converted from one degree of freedom associated with the beam to another. The converter consists of two pairs of slits (for the input and output fields), with a half-wave plate, a polarizing beam splitter and a non-polarizing beam splitter placed between them. Measurement of the output fields’ coherency matrix and spatial interference patterns confirm that the scheme operates as expected.