Bell correlations of a thermal fully connected spin chain in the vicinity of a quantum critical point

Bell correlations are among the most exotic of the phenomena through which quantum mechanics manifests itself. Their presence signals that the system may violate the postulates of local realism-conjectures once thought to be to be a non-negotiable property of the physical world. The importance of Bell correlations from this fundamental point of view is even further clarified by their applications, ranging from quantum cryptography to quantum metrology and quantum computing. It is therefore of growing interest to characterize the "Bell content" of complex, scalable many-body systems. Here, we perform a detailed analysis of the character and strength of many-body Bell correlations in interacting multiqubit systems with particle exchange symmetry. Such a configuration can be described by an effective Schr & ouml;dinger-like equation, which allows precise analytical predictions. We show that in the vicinity of the quantum critical point, these correlations quickly become so strong that only a fraction of the qubits remain uncorrelated. We also identify the threshold temperature above which thermal fluctuations destroy Bell correlations. We hope that the approach presented here, due to its universality, will be useful for upcoming research on genuinely nonclassical Bell-correlated complex systems.