近日，丹麦哥本哈根大学的Peter Lodahl&Alexey Tiranov及其研究团队取得一项新进展。经过不懈努力，他们通过双能级发射极上光子散射实现贝尔不等式的违反。相关研究成果已于2024年6月19日在国际知名学术期刊《自然—物理学》上发表。
该研究团队展示了如何在纳米光子波导中使用单个双能级发射器与光确定性耦合来实现单光子水平的光子量子纠缠。有效的光耦合使发射器能够调解双光子相互作用，从而产生导致纠缠的强非线性。研究人员通过双光子散射响应的干涉测量实验，验证了能量-时间纠缠，并成功违反了贝尔不等式。此过程中的片上两级发射器作为被动的散射体，无需复杂的自旋控制。因此，这一方法为量子模拟器或量子计量学提供了一种更高效的光子纠缠态合成途径。
据悉，纠缠是多体量子系统中存在的非局域相关，是量子技术的关键资源。因此，开发简单而节能的方法来产生高保真纠缠态是一个主要的优先事项。在光的情况下，纠缠可以通过与物质的相互作用来实现，但所需的非线性相互作用通常是不切实际的弱。
附：英文原文
Title: Violation of Bell inequality by photon scattering on a two-level emitter
Author: Liu, Shikai, Sandberg, Oliver August DallAlba, Chan, Ming Lai, Schrinski, Bjorn, Anyfantaki, Yiouli, Nielsen, Rasmus B., Larsen, Robert G., Skalkin, Andrei, Wang, Ying, Midolo, Leonardo, Scholz, Sven, Wieck, Andreas D., Ludwig, Arne, Srensen, Anders S., Tiranov, Alexey, Lodahl, Peter
Issue&Volume: 2024-06-19
Abstract: Entanglement, the non-local correlations present in multipartite quantum systems, is a key resource for quantum technologies. It is therefore a major priority to develop simple and energy-efficient methods for generating high-fidelity entangled states. In the case of light, entanglement can be realized by interactions with matter but the required nonlinear interaction is often impractically weak. Here we show how a single two-level emitter deterministically coupled to light in a nanophotonic waveguide can be used to realize photonic quantum entanglement by excitation at the single-photon level. Efficient optical coupling enables mediation of two-photon interactions by the emitter, creating a strong nonlinearity that leads to entanglement. We experimentally verify energy–time entanglement by violating a Bell inequality in an interferometric measurement of the two-photon scattering response. The on-chip two-level emitter acts as a passive scatterer, so that no advanced spin control is required. As such, our method may provide a more efficient approach to synthesizing photonic entangled states for quantum simulators or metrology.
DOI: 10.1038/s41567-024-02543-8
Source: https://www.nature.com/articles/s41567-024-02543-8