ENTANGLEMENT-INDUCED 2-PHOTON TRANSPARENCY

The rate of absorption of entangled photon pairs is linear in the phot on-flux density. We demonstrate that the two-photon absorption cross s ection :is a nonmonotonic function of the entanglement time; it vanish es for certain energy-level configurations and values of the: entangle ment time. This entanglement-induced two-photon transparency arises fr om the coherent summation of transition-amplitude contributions over t he finite entanglement time. As an example, the entangled two-photon c ross section for the 1S-2S electronic transition in atomic hydrogen is obtained.