Applications of electromagnetically induced transparancy in quantum information

Electromagnetically induced transparency (EIT) has been used to slow down and store light pulses coherently. Since decoherence is suppressed in this process, EIT is an interesting technique to manipulate quantum states of light. In this talk I will present recent work done at the Institute for Quantum Information Science on using EIT to process quantum information. One project is concerned with the detection of atomic entanglement. If atoms are cooled by the method of velocity-selective coherent population trapping, they settle in an entangled superposition of electronic and center-of-mass degrees of freedom. We predict that this entanglement will give rise to a coherently backscattered light pulse if the gas is probed with a weak laser pulse. A second project is the manipulation of single-photon states by means of an adiabatic Raman technique in a Lambda system with multiple excited states. We have shown that in such a system exactly one superposition of photonic modes can exhibit EIT. By changing the control fields this superposition can be changed and allows to manipulate the quantum state of light.