Reservoir-mediated spin entanglement in the mean-force Gibbs state

• URL: http://arxiv.org/abs/2604.26562v1
• Date: Wed, 29 Apr 2026 11:48:28 GMT
• Title: Reservoir-mediated spin entanglement in the mean-force Gibbs state
• Abstract summary: Two qubits strongly coupled to a bosonic reservoir can become entangled with each other, despite having no direct interaction.<n>In equilibrium, such coupling-induced coherences can be described by the mean-force Gibbs state.<n>We find that broadening the reservoir spectral density beyond a single mode, as is realistic for typical baths, can enhance the qubit entanglement.
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• License: http://creativecommons.org/licenses/by/4.0/
• Abstract: Two qubits strongly coupled to a common bosonic reservoir can become entangled with each other, despite having no direct interaction. In equilibrium, such coupling-induced coherences can be described by the mean-force Gibbs state. Here we derive approximate, analytic expressions for the two-qubit mean-force Gibbs state, and use these to characterize equilibrium qubit-qubit entanglement mediated by a thermal reservoir. Entanglement, which is highest at lowest temperatures, is a non-monotonic function of the system-reservoir coupling strength. Moreover, we find that broadening the reservoir spectral density beyond a single mode, as is realistic for typical baths, can enhance the qubit entanglement. Our results provide a comprehensive understanding of reservoir-mediated two-qubit entanglement in thermal equilibrium and provide a benchmark to compare with numerical methods, as well as demonstrating the utility of strong system-reservoir coupling as a resource.

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