  We derive a set of optical Bloch equations (OBEs) directly from the
minimal-coupling Hamiltonian density of the bound-state quantum electrodynamics
(bound-state QED). Such optical Bloch equations are beyond the former
widely-used ones due to that there is no electric dipole approximation (EDA) on
the minimal-coupling Hamiltonian density of the bound-state QED. Then our
optical Bloch equations can describe a two-level atom interacting with a
monochromatic light of arbitrary wavelength, which are suitable to study the
spectroscopy and the Rabi oscillations of two-level atoms in X-ray laser beams
since that the wavelength of X-ray is close to an atom to make the electric
dipole approximation (EDA) invalid.
