上海纽约大学Chandrashekar Radhakrishnan团队近日研究了三方量子不谐的实验测定。2025年7月2日，《美国科学院院刊》杂志发表了这一成果。
量子不和谐是量子系统中非经典关联的度量。虽然量子不和谐的二分版本在实验上得到了很好的研究，但多分版本从未被令人信服地测量过。研究组使用核磁共振量子信息处理器对三重量子不和谐进行了实验研究。基于条件投影测量和量子条件互信息的理论框架，他们量化了三重量子不和谐及其在不同三量子比特态中的贡献，如Greenberger-Horne-Zeilinger（GHZ）和Werner（W）态，以及双可分贝尔态的经典混合物和乘积态的经典混合。
实验采用全量子态层析成像和时间平均来制备混合态，实现了超过95%的保真度。该研究结果证实，即使在没有纠缠的情况下，量子不和谐也会持续存在，这突显了它作为量子相关性更广泛指标的实用性。此外，研究组验证了不和谐的非纠缠性，证实了零不和谐状态的经典混合物可以表现出非零不和谐。这一实验证实，量子不和谐不符合资源理论的框架。这项工作建立了一种测量量子不和谐的稳健方法，阐明了多体系统中量子关联的结构和分布。
附：英文原文
Title: Experimental determination of tripartite quantum discord
Author: Gulati, Vaishali, Bhowmick, Shaileyee, Byrnes, Tim, Radhakrishnan, Chandrashekar, Dorai, Kavita
Issue&Volume: 2025-7-2
Abstract: Quantum discord is a measure of nonclassical correlations in quantum systems. While the bipartite version of quantum discord is experimentally well-studied, the multipartite version has never been convincingly measured. In this study, we experimentally investigate tripartite quantum discord using an NMR quantum information processor. Building on a theoretical framework for conditional projective measurements and quantum conditional mutual information, we quantify the tripartite quantum discord and its contributions in different three-qubit states such as the Greenberger-Horne-Zeilinger (GHZ) and Werner (W) states as well as classical mixtures of biseparable Bell states, and classical mixtures of product states. The experiments employed full quantum state tomography and temporal averaging to prepare mixed states, achieving fidelities exceeding 95%. Our results confirm that quantum discord persists even in the absence of entanglement, highlighting its utility as a broader indicator of quantum correlations. Furthermore, we validate the nonconvexity of discord, confirming that classical mixtures of zero-discord states can exhibit nonzero discord. This experimentally confirms that quantum discord does not fit into the framework of resource theory. This work establishes a robust methodology for measuring quantum discord, illuminating the structure and distribution of quantum correlations in multipartite systems.
DOI: 10.1073/pnas.2507467122
Source: https://www.pnas.org/doi/abs/10.1073/pnas.2507467122