Swapping and entangling qubits of single photons and atoms

A scheme is proposed here to achieve swapping and entangling of photonic and atomic qubits with high fidelity. The mechanism is based on the scattering of a single photon from a $\Lambda$-type three-level atom. The evolution of the coupled system is analyzed by projecting the quantum state onto a `bright' and a `dark' state. Quantum interference of these two states, which is determined by a frequency-dependent phase angle, can be exploited to perform various two-qubit transformations. It is remarkable that the probability of success of such transformations can approach unity in the strong coupling cavity QED regime.