  In spite of the fact that photons do not interact with an external magnetic
field, the latter field may indirectly affect photons in the presence of a
charged environment. This opens up an interesting possibility to continuously
control the entanglement of photon beams without using any crystalline devices.
We study this possibility in the framework of an adequate QED model. In an
approximation it was discovered that such entanglement has a resonant nature,
namely, a peak behavior at certain magnetic field strengths, depending on
characteristics of photon beams direction of the magnetic field and parameters
of the charged medium. Numerical calculations illustrating the above-mentioned
resonant behavior of the entanglement measure and some concluding remarks are
presented.
