发表机构
East China Normal University; National University of Singapore; Universiteit Leiden; Sun Yat-sen University; Quantum Science Center of Guangdong–Hong Kong–Macao Greater Bay Area (Guangdong)（华东师范大学; 新加坡国立大学; 莱顿大学; 中山大学; 粤港澳大湾区量子科学中心（广东））
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究证明利用少体置换不变关联即可认证多体贝尔关联，通过六、八光子Dicke态实验验证，显著提升噪声容忍度，为大型系统提供无需全体系测量的可行认证方案。
AI 中文摘要
在多体量子系统中认证贝尔关联日益具有挑战性，因为传统贝尔不等式依赖于多体关联，而随着系统规模增大，这些关联的实验估计变得困难。在此，我们证明可以使用具有固定最大关联阶的少体置换不变（PI）关联来认证多体贝尔关联。我们实验测试了为六光子和八光子后选择Dicke态量身定制的少体PI贝尔关联见证者。发现添加少量四体关联子可显著增强噪声容忍度，与先前研究的二体见证者相比：例如，对于六量子比特，所选见证者容忍的白噪声分数为$p_c\approx0.301$，而每方两个设置的最佳二体PI不等式仅为$p_c\approx0.048$。对于六光子和八光子，我们分别观察到见证者界限被违反$32$和$8.9$个标准差，这些违反来自后选择的偏振态，其与相应半激发Dicke态的保真度分别为$0.933(4)$和$0.916(11)$。六光子和八光子情况下的见证者使用相同的对称二体和四体关联子，只是系数不同。这些结果展示了一种实验上可行的方法，无需全体系关联测量即可在更大系统中认证多体贝尔关联。
英文摘要
Certifying Bell correlations in increasingly larger multipartite quantum systems is challenging because conventional Bell inequalities rely on many-body correlations, which become experimentally demanding to estimate as system size grows. Here we demonstrate that multipartite Bell correlations can be certified using few-body permutation-invariant (PI) correlations with a fixed maximal correlation order. We experimentally test few-body PI Bell correlation witnesses tailored for six- and eight-photon postselected Dicke states. The addition of a few four-body correlators is found to significantly enhance the noise tolerance compared with previously studied two-body witnesses: for instance, for six qubits, the selected witness tolerates a white-noise fraction of $p_c\approx0.301$, compared with $p_c\approx0.048$ for the best two-body PI inequality with the same two settings per party. For six and eight photons respectively, we observe violations of the witness bounds by $32$ and $8.9$ standard deviations, arising from postselected polarisation states with fidelities of $0.933(4)$ and $0.916(11)$ to the corresponding half-excitation Dicke states. The witnesses for the six- and eight-photon cases use the same symmetric two- and four-body correlators, just with different coefficients. These results demonstrate an experimentally accessible approach for certifying multipartite Bell correlations in larger systems without requiring full-body correlation measurements.
Comments36 pages, 5 figures, comments are welcome
