Increasing angular entanglement of spontaneous parametric down-conversion biphoton states via noncollinearity and the walk-off effect

Angular entanglement is investigated theoretically in various realizable regimes of SPDC. It is shown, in particular, that in the sufficiently well pronounced, noncollinear regime the degree of angular entanglement grows with increasing degree of noncollinearity. A rather specific dependence is found for the degree of entanglement in its dependence on the varying influence of the so-called walk-off effect of the pump in the SPDC crystal. A joint influence of the walk-off and noncollinearity is found to partly suppress the degree of angular entanglement.