  An entanglement-preserving photo-detector converts photon polarization to
electron spin. Up and down spin must respond equally to oppositely polarized
photons, creating a requirement for degenerate spin energies, ge=0 for
electrons. We present a plot of ge-factor versus lattice constant, analogous to
bandgap versus lattice constant, that can be used for g-factor engineering of
III-V alloys and quantum wells
