Faculty @ RIKEN, Japan

Wednesday June 29 – 8.00 BST

Effective cancellation of the current-dissipation trade-off by quantum coherence

In recent years, various kinds of trade-off relations between the current and the entropy production have been derived in the field of stochastic thermodynamics. One of the important insights that can be gained from these trade-off relations is that a simultaneous maximization of the thermodynamic efficiency and the output power of heat engines is not possible. While the trade-off relations have been successful in many applications ranging from biomolecular processes to thermoelectric junctions, the effect of quantum coherence was not clear. Here, we focus on the current-dissipation trade-off relation which sets a bound on both enhancing the heat current and suppressing the entropy production, simultaneously. By analyzing the effect of coherence on the current-dissipation ratio, we find that coherence between different energy eigenstates always increases the entropy production, thereby worsening the current-dissipation ratio. On the other hand, we find that coherence between degenerate states may improve the current-dissipation ratio. When the amount of coherence between degenerate states is large enough, the trade-off relation is effectively cancelled, and the heat current scales at the same order as the particle number while suppressing the entropy production at a constant order. By utilizing the above scaling analysis, we show a quantum heat engine model that asymptotically reaches the Carnot efficiency with finite output power, and explain how this finding is consistent with the power-efficiency trade-off relation. 

[H. Tajima and K. Funo, Phys. Rev. Lett. 127, 190604 (2021)].