  In this work, we extend the recently established system-bath entanglement
theorem (SBET) [J. Chem. Phys. 152, 034102 (2020)] to the nonequilibrium
scenario, in which an arbitrary system couples to multiple Gaussian baths
environments at different temperatures. While the existing SBET connects the
entangled system-bath response functions to those of local systems, the
extended theory is concerned with the nonequilibrium steady-state quantum
transport current through molecular junctions. The new theory is established on
the basis of the generalized Langevin equation, with a close relation to
nonequilibrium thermodynamics in the quantum regime.
