Energy-time entanglement from a resonantly driven quantum-dot three-level system

Abstract

Entanglement is a major resource in advanced quantum technology where it can enable a secure exchange of information over large distances. Energy-time entanglement is particularly attractive for its beneficial robustness in fiber-based quantum communication and can be demonstrated in the Franson interferometer. We report on Franson-type interference from a resonantly driven biexciton cascade under continuous wave excitation. Our measurements yield a maximum visibility of (73±2)% surpassing the limit of violation of Bell's inequality (70.7%) by more than one standard deviation. Despite being unable to satisfy a loophole free violation, our work demonstrates promising results concerning future studies on such a system. Furthermore, our systematical investigations on the impact of driving strength indicate that dephasing mechanisms and deviations from the cascaded emission have a major impact on the degree of the measured energy-time entanglement.