Summary:
We consider quantum electrodynamics, as a complex system, which consists of a
subsystem (the electrons) and it's environment (the electromagnetic field). The
dynamics of the open subsystem, can only bee done, thru it's density matrix. In
order to calculate it, we start from the total density matrix of the complex
system, we integrate over the environmental degrees of freedom and by following
the logic of Feynman and Vernon, we arive to the so called influence
functional. The non trivial integration over the field degrees of freedom, is
beeing done via the technic of the close complex time, which is related to the
Keldysh formalism, which is applicable to non equilibrium systems. For a
physical realisation of the result, we adopt a semiclassical approximation for
the electron's currents and we study a procedure, in which, decoherence
phenomena can appear.
Keywords:
Time evolution, Density matrix, Functional integral, Influence functional, Decoherence
