  Using the self-consistent Born approximation we study the delocalization of
interlayer excitons in the bilayer Heisenberg quantum antiferromagnet. Under
realistic conditions we find that the coupling between the exciton motion and
the spin system is strongly enhanced as compared to the case of a single
carrier, to a degree that it mimics the confinement physics of carriers in
Ising spin systems. We predict that the "ladder spectrum" associated with this
confinement physics should be visible in the c-axis exciton spectra of
insulating bilayer cuprates such as YBa2Cu3O6. Our discovery indicates that
finite density systems of such excitons should show very rich physical
behavior.
