Photon switching in a four-level atomic system based on quantum interference enhanced nonlinear absorption and inhibited linear absorption was reported. A vapor-cell magneto-optical trap (MOT) produced in the centre of stainless steel vacuum chamber was used to experimentally observe photon switching by quantum interference. A pulsed, stepwise probe transmission profile was obtained by a switching pulse used to control probe absorption. Analysis suggested that quantum interference inhibited single-photon absorption but enhanced third-order, two-photon-type absorption in a four-level system.
