We report an experimental demonstration of photon switching by quantum interference in a four-level atomic system proposed by Harris and Yamamoto (Phys. Rev. Lett. 81, 3611 (1998)). Quantum interference inhibits single-photon absorption but enhances third-order, two-photon type absorption in the four-level system. We have observed greatly enhanced nonlinear absorption in the four-level system realized with cold 87Rb atoms and demonstrated fast switching of the nonlinear absorption with a pulsed pump laser.
@article{arxiv.physics/0105065,
title = {Observation of absorptive photon switching by quantum interference},
author = {Min Yan and Edward G. Rickey and Yifu Zhu},
journal= {arXiv preprint arXiv:physics/0105065},
year = {2009}
}