Cavity electromagnetically induced transparency and all-optical switching using ion Coulomb crystals

The control of one light field by another, ultimately at the single photon level(1-7), is a challenging task that has numerous interesting applications within nonlinear optics(4,5) and quantum information science(6-8). This type of control can only be achieved through highly nonlinear interactions, such as those based on electromagnetic induced transparency (EIT)(2-6,9-12). Here, we demonstrate for the first time EIT as well as all-optical EIT-based light switching using ion Coulomb crystals situated in an optical cavity. Changes from essentially full transmission to full absorption of a single photon probe field are achieved within unprecedentedly narrow EIT windows of a few tens of kilohertz. By applying a weak switching field, this allows us to demonstrate nearly perfect switching of the transmission of the probe field. The results represent important milestones for future realizations of quantum information processing devices, such as high-efficiency quantum memories(8,13,14), single-photon transistors(15,16) and single-photon gates(4,6,9).