Year: 2026
Type: article
Abstract: Real refrigerators operate in finite time, deviating from classical thermodynamics, which predicts zero cooling power at Carnot efficiency. Finite-time thermodynamics (FTT) addresses this by incorporating realistic constraints, but quantum extensions often rely on the weak-coupling approximation. This approximation fails in systems—such as superconducting circuits or nanomechanical resonators—where qubit-bath interactions are strong. To overcome this, we study a one-qubit refrigerator using the non-perturbative reaction-coordinate polaron transform (RCPT), which systematically captures strong-coupling effects through an exact mapping and dressing of a collective bath mode. We derive the renormalized qubit energy and effective dissipation rates, leading to a closed expression for the steady-state cooling power $$Q_{\text {c}}^{\text {RCPT}}(\lambda )$$ Q c RCPT ( λ ) . Numerical optimization reveals a critical coupling strength $$\lambda _{\text {c}} \approx 0.71$$ λ c ≈ 0.71 beyond which cooling performance deteriorates sharply. We analyze the impact of coupling strength on the maximum cooling power, the trade-off function $$\Omega$$ Ω , and a family of figures of merit $$\varepsilon ^I Q_{\text {c}}$$ ε I Q c . Our results establish the validity bounds of the weak-coupling approximation and demonstrate that excessive coupling suppresses energy extraction, providing essential guidelines for designing robust quantum thermal devices in the strong-coupling regime.
Author: J. J. Fernández
Institution: Universidad Nacional de Educación a Distancia
Language: English
Subfield: Statistical and Nonlinear Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $3,890
Award: G46323293
OpenAlex ID: W7127450690