  The recently developed Wigner functional theory is used to formulate an
evolution equation for arbitrary multi-photon states, propagating through a
turbulent atmosphere under arbitrary conditions. The resulting evolution
equation, which is obtained from an infinitesimal propagation approach, is in
the form of a Fokker-Planck equation for the Wigner functional of the state and
therefore incorporates functional derivatives. We show consistency with
previously obtained solutions from different approaches and consider possible
ways to find additional solutions for this equation.
