Summary form only given. A coupling laser can create electromagnetically induced transparency (EIT) in an absorbing medium such that linear absorption of a weak probe laser at the line center is suppressed by quantum interference. The quantum interference may be modified by adding a pump laser coupled to a separate state, which leads to enhanced third-order nonlinearities in the atomic system. Large nonlinear probe absorption at the EIT center is controlled by the pump laser and may be used to realize absorptive photon switching as proposed by Harris and Yamamoto. We report an experimental study of enhanced third-order nonlinear absorption and absorptive photon switching in 87Rb atoms cooled and confined in a magneto-optical trap.
