Abstract

Biphoton states arising in the process of spontaneous parametric down-conversion (SPDC) are entangled with respect to continuous variables, momentum or coordinates. We discuss some novel and unexpected features of biphoton wave packets. We find that angular structure of the states emitted via SPDC and observable degree of entanglement is strongly anisotropic. Recently the operational method, which allows one to determine the degree entanglement in bipartite systems with continuous variables, has been suggested. It turns out that the degree of entanglement is related to quantities, which can be easily measured in experiment R = Δk^s/Δk^c: where Δk^s and Δk^c are widths of single-particle and coincidence distributions.

© 2007 IEEE