  Entangled photon states attract tremendous interest as the most vivid
manifestation of nonlocality of quantum mechanics and also for emerging
applications in quantum information. Here we propose a mechanism of generation
of polarization-entangled photons, which is based on the nonlinear optical
interaction (four-wave mixing) in graphene placed in a magnetic field. Unique
properties of quantized electron states in a magnetized graphene and optical
selection rules near the Dirac point give rise to a giant optical nonlinearity
and a high rate of photon production in the mid/far-infrared range.
