  Spin-entaglement has been proposed and extensively used in the case of
correlated triplet pairs which are intermediate states in singlet fission
process in select organic semiconductors. Here, we employ quantum process
tomography of polarization entangled photon-pairs resonant with the excited
state absorption of these states to investigate the nature of the inherent
quantum correlations and to explore for an unambiguous proof for the existence
of exciton entanglement.
