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arXiv · 2608.09461

Probing Non-equilibrium baths: Frequency-Resolved Thermometry and Quantum Heat Current Turnover

Akhil Bhartiya·Tobias Kramer·David Gelbwaser-Klimovsky
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Abstract

Quantum heat transport for non-equilibrium steady state (NESS) exhibits a characteristic turnover effect, where the heat current reaches a maximum and subsequently declines as system-bath coupling increases. Although numerically exact methods can simulate this non-monotonic behavior, they offer limited information on the thermal state of the heat baths. Here, we introduce a frequency-selective thermometric protocol to probe the baths sustaining an NESS. By extracting a frequency-resolved effective temperature spectrum using a tunable two-level probe, we demonstrate that spectral dispersion serves as a direct witness for the non-equilibrium state of the heat baths. To demonstrate the protocol, we applied the hierarchical equations of motion to spin-boson and two-qubit models, though any exact method can be used. For both models, the turnover effect can be explained by how the thermal state of the heat baths evolves as the system-bath coupling strength increases.

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Akhil Bhartiya, Tobias Kramer, David Gelbwaser-Klimovsky. 2026-08-10. Probing Non-equilibrium baths: Frequency-Resolved Thermometry and Quantum Heat Current Turnover. https://arxiv.org/abs/2608.09461

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