  Present proposals for the realisation of entangled photon pair sources using
the radiative decay of the biexciton in semiconductor quantum dots are limited
by the need to enforce degeneracy of the two intermediate, single exciton
states. We show how this requirement is lifted if the biexciton binding energy
can be tuned to zero and we demonstrate this unbinding of the biexciton in a
single, pre-positioned InAs quantum dot subject to a lateral electric field.
Full Configuration-Interaction calculations are presented that reveal how the
biexciton is unbound through manipulation of the electron-hole Coulomb
interaction and the consequent introduction of Hidden Symmetry.
