Control of entanglement and two-qubit quantum gates with atoms crossing   a detuned optical cavity
  A scheme is proposed to generate an entangled state between two (Lambda-type) four-level atoms that interact effectively by means of a detuned optical cavity and a laser beam that acts perpendicularly to the cavity axis. It is shown how the degree of entanglement for two atoms passing through the cavity can be controlled by manipulating their velocity and the (initial) distance between the atoms. In addition, three realistic schemes are suggested to implement the two-qubit gates within the framework of the suggested atom-cavity-laser setup, namely, the i-swap gate, controlled-Z gate and the controlled-NOT gate. For all these schemes, we analyze and discuss the atomic velocities and inter-atomic distances for which these gates are realized most reliably. 
D. Gonta and S. Fritzsche