Richness of Bell Nonlocality: Team Demonstrates Simultaneous Violation of -Qubit Bell Inequalities with a Single State
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Bell nonlocality, a fundamental feature of quantum mechanics, underpins modern technologies and challenges our classical understanding of the world. Gerard Anglès Munné, Paweł Cieśliński, and Jan Wójcik, along with Wiesław Laskowski, all from the Institute of Theoretical Physics and Astrophysics at the University of Gdańsk, have significantly expanded our knowledge of this phenomenon. Their research demonstrates that, unlike simpler two-particle systems where nonlocality is limited, multipartite systems exhibit a remarkable ‘polygamy’, the ability to violate multiple Bell inequalities simultaneously.
The team not only generalised this polygamous behaviour to apply to any number of particles, but also discovered ‘hyper-polygamy’, where this occurs across multiple subsystem sizes, revealing a surprising richness in the ways quantum systems can display non-classical correlations. This achievement provides new insights into certifying quantum behaviour in complex devices and opens exciting possibilities for future quantum technologies. Nonlocality represents a central example of quantum behaviour. For bipartite Bell inequalities, nonlocal correlations obey strict monogamy, meaning a violation of one inequality precludes violations of others on overlapping subsystems. However, in multipartite systems, Bell nonlocality becomes inherently polygamous.
This research generalizes previous work, demonstrating that a single N-qubit state can violate all N relevant Bell inequalities simultaneously.
The team constructed an N-qubit Bell inequality, derived by symmetrizing smaller inequalities, that exhibits maximal violation.
Polygamous Entanglement Beyond Simple Monogamy This research delves into the fascinating world of quantum nonlocality, specifically focusing on the polygamous nature of Bell correlations. The study expands upon the concepts of entanglement monogamy and polygamy, exploring how many parties can share entanglement simultaneously. Key findings include expanding the understanding of polygamy, deriving novel Bell inequalities, and establishing tighter bounds on the degree of polygamy achievable for various quantum states. A significant focus lies on permutationally invariant states, which are particularly relevant for experimental realization and analysis. The research emphasizes finding criteria and inequalities that are experimentally accessible for verifying theoretical predictions, and touches upon self-testing, where Bell inequality violation certifies entanglement without full state tomography. This work builds upon previous research on Bell inequalities and multipartite entanglement, with implications for quantum communication, quantum cryptography, and the development of quantum technologies. Generalized Polygamy and Hyper-Polygamy Demonstrated in Qubits Scientists demonstrate that a single N-qubit state can simultaneously violate all relevant Bell inequalities, a phenomenon termed generalized polygamy.
This research establishes that this polygamous behaviour extends across multiple subsystem sizes, a characteristic the team calls hyper-polygamy, revealing an abundance of nonlocality in multipartite states.
The team constructed an N-qubit Bell inequality, derived by symmetrizing smaller inequalities, that is maximally violated by states exhibiting this generalized polygamy. Measurements confirm that these polygamous states offer an advantage over GHZ states in multipartite scenarios, providing new insights into scalable certification of non-classicality.
The team compared the violations achieved by polygamous states and GHZ states, and results show that for k 1, the polygamous states consistently outperform the GHZ strategy. Specifically, the team established that the highest value of this measure is achieved by states exhibiting this polygamous behaviour. For a two-party system (k=2), the team discovered that optimal violations are possible starting from six qubits, compared to seven for other methods.
Polygamous Bell Nonlocality in Multipartite Systems This research demonstrates a surprising abundance of non-classical correlations within multipartite quantum systems, specifically focusing on polygamy in Bell nonlocality.
Scientists have shown that a single quantum state can simultaneously violate numerous Bell inequalities, revealing that these systems possess a greater capacity for demonstrating quantum behaviour than previously thought.
The team constructed a family of quantum states that exhibit this polygamous behaviour, violating all possible Bell inequalities of a given size concurrently. Importantly, the number of these simultaneously violated inequalities scales extensively with the number of qubits.
This research further introduces the concept of ‘hyper-polygamy’, where a single state demonstrates polygamous behaviour across multiple subsystem sizes, with observations of up to 28 simultaneous violations in a seven-qubit system. While the study determined minimal system sizes needed to observe hyper-polygamy, they note that this behaviour diminishes in larger systems. These findings have implications for the development of quantum technologies, particularly in quantum networks, offering a pathway to improve benchmarks for quantum devices and potentially enable device-independent self-testing of multiple nodes. 👉 More information 🗞 The Richness of Bell Nonlocality: Generalized Bell Polygamy and Hyper-Polygamy 🧠 ArXiv: https://arxiv.org/abs/2512.09034 Tags: