Collective phenomena in quantum thermodynamics: from mitigation to amplification of the baths' action

An increasing number of papers in quantum thermodynamic have shown that collective effects can be beneficial for thermodynamic tasks. In order to understand better why and when such enhancements can happen, we analyse in details the energetic, entropic, and more generally thermodynamic consequences of collective coupling between an ensemble of identical systems (spin or atoms) and their bath.
We reach the conclusion [1] that collective coupling, through the coherences it intrinsically generates, effectively shield the ensemble from the bath's action, affecting dramatically the thermodynamic characteristic of the ensemble (energy, entropy, and free energy). Strikingly, in presence of two thermal baths, the combination of these mitigation effects can result in a great amplification of the baths' action. This is illustrated through a cyclic (Otto) thermal machine, resulting in a large output power enhancement. We also highlight that such enhancements are not systematic: depending on the value of the bath temperatures, the number of spins, and their dimension, either enhancement or degradation of performances can happen.

[1] C. L. Latune, I. Sinayskiy, and F. Petruccione, arXiv:1908.10384