Charge transport in inhomogeneous quantum systems in weak   electro-magnetic fields: two-time Green's function approach
  A first principle theory of charge transport in spatially inhomogeneous quantum systems composed of any finite number of particles and subject to weak electro-magnetic fields is developed. Simple analytical expressions for the linear contributions to the quantum susceptibilities and conductivity tensors, and the charge and current densities of such systems are derived in terms of two-time Green's functions. The obtained results can be applied to description of quantum charge transport in any finite system, including small semiconductor quantum dots, artificial molecules and atoms, etc.   PACS: 05.60.Cg, 05.30.-d, 03.65Yz, 73.63.-b, 03.65.Db 
Liudmila A. Pozhar