Nonequilibrium Energy Transfer at Nanoscale: A Unified Theory from Weak   to Strong Coupling
  We investigate the microscopic mechanism of quantum energy transfer in the nonequilibrium spin-boson model. By developing a nonequilibrium polaron-transformed Redfield equation based on fluctuation decoupling, we dissect the energy transfer into multi-boson associated processes with even or odd parity. Based on this, we analytically evaluate the energy flux, which smoothly bridges the transfer dynamics from the weak spin-boson coupling regime to the strong-coupling one. Our analysis explains previous limiting predictions and provides a unified interpretation of several observations, including coherence-enhanced heat flux and absence of negative differential thermal conductance in the nonequilibrium spin-boson model. The results may find wide applications for the energy and information control in nanodevices. 
Chen Wang, Jie Ren, and Jianshu Cao
cond-mat.mes-hall