Suppose some system of interacting qubits interacts with two baths at different temperatures, what is the steady-state average flow of heat from the hot bath to the cold bath? A set-up of this type was recently investigated by Pekola and his group (Ronzani et al, Nature Physics 2018). The problem can be treated in perturbation theory assuming that system jumps are caused by separate interactions with the baths, each of which transfers a quantum of energy to or from a bath. This theory agrees well with experiments when coupling is weak. Here I will consider just one qubit coupled with two baths as in the spin-boson model. In an approximation analogous to `non-interacting blip’ (NIBA) one can solve for thermal power of heat to the cold bath in terms of certain correlation functions of the two baths. I will discuss the qualitative differences and similarities between weak-coupling and strong-coupling in such a setting.
This is joint work with F Montana, arXiv:1901.05896