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Thermodynamic uncertainty relation of a quantum mechanically coupled two-qubit system

Kwang Hyun Cho*

Hyukjoon Kwon† and Changbong Hyeon‡

  • *Contact author: khcho@kias.re.kr
  • †Contact author: hjkwon@kias.re.kr
  • ‡Contact author: hyeoncb@kias.re.kr
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Phys. Rev. Research 7, 033132 – Published 8 August, 2025

DOI: https://doi.org/10.1103/8wjq-ns94

Abstract

The minimal bound of the thermodynamic uncertainty relation (TUR) is modulated from that of the classical counterpart (Qmin=2) when a quantumness is present in the dynamical process far from equilibrium. A recent study on a dissipative two-level system (TLS) subject to an external field indicates that quantum coherence can suppress the fluctuations of the irreversible current and loosens the TUR bound to QminTLS≈1.25. Here, by extending the field-driven single TLS to a quantum mechanically coupled two-qubit system (TQS), we explore how the quantum coupling between the two qubits, an additional complexity introduced to the probem of TLS, affects the photon current, fluctuations, and the TUR bound. We find that the TUR bound of the TQS depends on the strength of coupling, such that QminTQS=QminTLS≈1.25 when the two qubits are effectively decoupled under weak coupling, whereas another loose bound QminTQS≈1.36 is identified for two strongly coupled qubits under strong fields. By contrasting the TQS against two coupled noisy oscillators, we illuminate the quantumness unique to the TQS and its effect on the TUR. Our findings from the study of the TQS form the basis for understanding the TUR of more general N-qubit systems.

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Phys. Rev. Research 7, 033132– Published 8 August, 2025
  • Received 6 May 2025
  • Accepted 17 July 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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