title: Generation of two-photon States with an arbitrary degree of entanglement via nonlinear crystal superlattices.
abstract: We demonstrate a general method of engineering the joint quantum state of photon pairs produced in spontaneous parametric down-conversion. The method makes use of a superlattice structure of nonlinear and linear materials, in conjunction with a broadband pump, to manipulate the group delays of the signal and idler photons relative to the pump pulse, and realizes photon pairs described by a joint spectral amplitude with arbitrary degree of entanglement. This method of group-delay engineering has the potential of synthesizing a broad range of states including factorizable states crucial for quantum networking and states optimized for Hong-Ou-Mandel interferometry. Experimental results for the latter case are presented, illustrating the principles of this approach.
authors.affiliation: Clarendon Laboratory, Oxford University, Parks Road, Oxford, OX1 3PU, United Kingdom.
authors.forename: Alfred B
authors.initials: AB
authors.lastname: U'Ren
authors.forename: Reinhard K
authors.initials: RK
authors.lastname: Erdmann
authors.forename: Manuel
authors.initials: M
authors.lastname: de la Cruz-Gutierrez
authors.forename: Ian A
authors.initials: IA
authors.lastname: Walmsley