  We study biexcitonic states in two tunnel-coupled semiconductor quantum dots
and show that such systems provide the possibility to produce polarization-
entangled photons or spin-entangled electrons that are spatially separated at
production. We distinguish between the various spin configurations and
calculate the low-energy biexciton spectrum using the Heitler-London
approximation as a function of magnetic and electric fields. The oscillator
strengths for the biexciton recombination involving the sequential emission of
two photons are calculated. The entanglement of the photon polarizations
resulting from the spin configuration in the biexciton states is quantified as
a function of the photon emission angles.
