Characterization of Spectral Entanglement of Spontaneous Parametric-Down Conversion Biphotons

TL;DR

This paper presents an experimental method to measure the spectral entanglement of biphotons generated by spontaneous parametric down-conversion, revealing potentially very high entanglement levels in pure biphoton states.

Contribution

It introduces a direct measurement approach for quantifying spectral entanglement in biphotons, providing an upper bound on entanglement in pure states.

Findings

Spectral distributions of single counts and coincidences were measured.

Entanglement quantifier calculated shows values up to 10^4-10^5.

The method provides an upper bound on biphoton entanglement.

Abstract

We verified operational approach based on direct measurement of entanglement degree for bipartite systems. In particular spectral distributions of single counts and coincidence for pure biphoton states generated by train of short pump pulses have been measured and entanglement quantifier calculated. The approach gives upper bound of entanglement stored in total biphoton states, which can reach extremely high value up to $10^{4}-10^{5}$.