Azimuthal entanglement and multimode schmidt decompositions for noncollinear biphotons

Noncollinear biphoton states are found to possess a very high degree of azimuthal entanglement with typical values of ~10 4 for Schmidt parameter K (the ratio of the pump wavelength to its waist). A scheme that provides conditions for Schmidt-type mode separation and multichannel Schmidt-type decomposition is proposed for the partial use of this enormous high-entanglement resource.