The dramatic impact of non-energetic coherences on heat flows

We show that the heat flow between a system and a stationary reservoir (under Born-Markov approximation) is dramatically affected by coherences between degenerate levels of the system. To assess the resulting effects of coherences on heat flows we introduce a concept of apparent temperature [1] which crucially takes into account coherences, by contrast with the virtual temperature [2]. It provides an intuitive picture in which non-energetic coherences behave as populations, enabling one to recover seminal results on phaseonium, thermally entangled atoms, and lasing without inversion. Moreover, we predict new effects like the dramatic increase of apparent temperature due to delocalised excitations. One of its manifestations, testable experimentally, is the “apparent thermalization”, where an ensemble of indistinguishable subsystems equilibrates at a much lower (or higher) energy than when interacting separately (or distinguishably) with the bath. Such phenomena stem from the mixture of the dynamics of the populations and coherences, which happens only in presence of degeneracy and is unique to quantum thermodynamics.
[1] C. L. Latune, I. Sinayskiy, F. Petruccione, arxiv:1803.11495.
[2] N. Brunner et al., Phys. Rev. E 85, 051117 (2012).