Lindbladian approach for many-qubit thermal machines: enhancing the performance with geometric heat pumping by interaction

We present a detailed analysis of slowly driven quantum thermal machines based on interacting qubits within the framework of the Lindblad master equation. By implementing a systematic expansion in the driving rate, we derive explicit expressions for the rate of work of the driving forces, the heat currents exchanged with the reservoirs, and the entropy production up to second order, ensuring full thermodynamic consistency in the linear-response regime. The formalism naturally separates geometric and dissipative contributions, identified by a Berry curvature and a metric in parameter space, respectively. Analytical results show that the geometric heat pumped per cycle is bounded by $k_B T N_q \ln 2$ for $N_q$ non-interacting qubits, in direct analogy with the Landauer limit for entropy change. This bound can be surpassed when qubit interactions and asymmetric couplings to the baths are introduced. Numerical results for the interacting two-qubit system reveal a non-trivial role of the interaction between qubits and the coupling between the qubits and the baths in the behavior of the dissipated power. The approach provides a general platform for studying dissipation, pumping, and performance optimization in driven quantum devices operating as heat engines.

💡 Research Summary

The paper develops a comprehensive theoretical framework for slowly driven quantum thermal machines composed of interacting qubits, based on the Lindblad master equation. Starting from a Hamiltonian describing $N_q$ spin‑½ qubits subject to time‑dependent magnetic fields $\mathbf B_j(t)$ and an exchange interaction $J$, the authors couple the system to $M$ bosonic thermal baths via weak system‑bath operators. By applying standard weak‑coupling, Born–Markov, and secular approximations, they obtain a Lindblad master equation for the “frozen” system at any instantaneous set of control parameters $\mathbf X$.

The core of the analysis is a systematic expansion in the small parameter $\tau^{-1}$, where $\tau$ is the driving period, i.e., a slow‑driving (adiabatic) expansion. The reduced density matrix is written as
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