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arXiv · 2511.17357

Optimal Thermalization under Indefinite Causal Order with Identical and Asymmetric Baths

Neeraj Sharma·Parveen Kumar
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Abstract

Indefinite causal order (ICO), in which the order of quantum operations is placed in a coherent superposition, has been demonstrated to enhance various information-processing tasks. Here, we investigate its impact on the thermodynamic processes generated by thermalizing quantum channels. We consider a two-level system interacting with two thermal baths under a quantum SWITCH, with the channel order controlled coherently by an ancillary qubit. We derive closed-form expressions for the effective inverse temperature $\beta_f$ of the postselected system state for both identical and distinct bath temperatures, and identify the control-qubit parameters that maximize heating or cooling. Our analysis reveals how the diagonal and coherent components of the control-qubit state contribute separately to the temperature shift, and how their interplay enables departures from the thermal response attainable under protocols with a definite causal order within the thermodynamic setting considered here. Bath asymmetry enhances these effects, while reduced purity of the control qubit state suppresses them. These results provide a systematic framework for assessing SWITCH-based thermalization in the setting of indefinite causal order, and identify control-qubit coherence as a tunable resource.

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Neeraj Sharma, Parveen Kumar. 2025-11-21. Optimal Thermalization under Indefinite Causal Order with Identical and Asymmetric Baths. https://doi.org/10.1103/zbgc-wdrk

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