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Physical Review Research

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

M. Hohn, Kisa Barkemeyer, Martin von Helversen, L. Bremer, Manuel Gschrey, J.-H. Schulze, A. Strittmatter, Alexander Carmele, Sven Rodt, S. Bounouar, Stephan Reitzenstein

Published Jun 22, 2023• 10 citations
Publisher

Abstract

We investigate the degree of energy-time entanglement in a dressed quantum-dot three-level system via Franson interferometry. Our work demonstrates a maximum visibility of (73 $\ifmmode\pm\else\textpm\fi{}$ 2)%, surpassing the limit of violation of Bell's inequality.

DOI
10.1103/physrevresearch.5.l022060

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In a recent Letter [Phys. Rev. Lett. 118, 030501 (2017)], Peiris, Konthasinghe, and Muller report a Franson interferometry experiment using pairs of photons generated from a two-level semiconductor quantum dot. The authors report a visibility of 66% and claim that this visibility "goes beyond the classical limit of 50% and approaches the limit of violation of Bell's inequalities (70.7%)." We explain why we do not agree with this last statement and how to fix the problem.

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We investigate the degree of energy-time entanglement in a dressed quantum-dot three-level system via Franson interferometry. Our work demonstrates a maximum visibility of (73 \ifmmode±\else\textpm\fi\ifmmode\pm\else\textpm\fi{}\ifmmode±\else\textpm\fi 2)%, surpassing the limit of violation of Bell's inequality.
Entanglement is a major resource in advanced quantum technology, where it can enable 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 ±\pm± 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 works on such a system. Furthermore, our systematical studies on the impact of driving strength indicate that dephasing mechanisms and deviations from the cascaded emission have major impact on the degree of the measured energy-time entanglement.
Resonance fluorescence from a coherently driven two-level emitter is a minimal quantum optical field that combines phase coherence with single-photon-level nonlinearity. Here we show that it can be engineered, using only passive linear interferometry, into energy-time entanglement. By injecting resonance fluorescence from a single quantum dot into an asymmetric Mach--Zehnder interferometer operated near destructive interference of the single-photon component, we generate an output field whose coincidence statistics are dominated by the simultaneous two-photon contribution |2> and the temporally separated photon-pair contribution |11>. In a Franson geometry, these two sectors are resolved on the coincidence-delay axis, and both exhibit high-visibility nonlocal interference fringes and violate the Clauser--Horne--Shimony--Holt Bell inequality. Our results reveal a general route for engineering entanglement from resonance fluorescence using passive optics.
We report a Franson interferometry experiment based on correlated photon pairs generated via frequency-filtered scattered light from a near-resonantly driven two-level semiconductor quantum dot. In contrast to spontaneous parametric down-conversion and four-wave mixing, this approach can produce single pairs of correlated photons. We have measured a Franson visibility as high as 66%, which goes beyond the classical limit of 50% and approaches the limit of violation of Bell's inequalities (70.7%).
Scalable quantum photonic technologies require deterministic sources of entangled photons that are compatible with established semiconductor manufacturing platforms. While self-assembled III-V semiconductor quantum dots are among the most promising sources of on-demand entanglement generation, their integration with silicon-based architectures remains a central challenge. Here, we demonstrate energy-time entanglement from a single InGaAs/GaAs quantum dot monolithically grown on a silicon substrate. Under resonant two-photon excitation, we achieve coherent control of the biexciton-exciton cascade, evidenced by the formation of dressed-states and Rabi oscillations. Using a four-channel Franson interferometer, we observe phase-dependent two-photon interference with visibilities up to (64.0 ± 7.0)% for a 80 ps integration window (and (49.4 ± 1.9)% for a 1600 ps window), approaching the threshold for Bell inequality violation at short timescales. Despite these constraints, the observation of Franson interference establishes monolithic III-V-on-silicon quantum dots as viable sources of energy-time entangled photons. These results represent a crucial step toward fully integrated, silicon-substrate-compatible quantum photonic circuits for large-scale quantum communication and information processing.