Characterization of spectral entanglement of spontaneous parametric-down conversion biphotons in femtosecond pulsed regime

Abstract

We verified the operational approach based on the direct measurement of the
\nentanglement degree for bipartite systems. In particular spectral distributions of single counts
\nand coincidence for pure biphoton states generated by a train of short pump pulses have been
\nmeasured and the entanglement quantifier has been calculated. The approach gives an upper
\nbound of entanglement stored in total biphoton states, which can reach extremely high values up
\nto 104–105.