  We describe two-photon absorption processes excited by entangled pairs, but
not by non-entangled pairs of the same energy and polarization. Photon states
are selected for destructive interference in the non-entangled process between
different sequences of absorption via multiple intermediate states. A non-zero
entangled absorption cross section is obtained by varying the entanglement time
and pair delay parameters. Detailed energy and polarization requirements are
derived for Rb 5S1/2 --> 5D3/2 transitions. Applications to Quantum
Steganography and Quantum Key Distribution are discussed.
