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

Hohn, Marcel; Barkemeyer, Kisa; von Helversen, M.; Bremer, L.; Gschrey, M.; Schulze, J.-H.; Strittmatter, A.; Carmele, A.; Rodt, S.; Bounouar, S.; Reitzenstein, Stephan

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.
Published in: Physical Review Research, 10.1103/physrevresearch.5.l022060, American Physical Society