An entanglement-preserving photodetector converts photon polarisation to el
ectron spin. Up and down spin must respond equally to oppositely polarised
photons, creating a requirement for degenerate spin energies, g(e) similar
or equal to 0, for electrons. The authors present a plot of g(e) factor aga
inst lattice constant, analogous to bandgap against lattice constant. that
can be used for g factor engineering of III-V alloys and quantum wells.