Fast CNOT gate via quantum Zeno dynamics

Based on the quantum Zeno dynamics, we propose two approaches for directly implementing a CNOT gate in a cavity QED system instead of constructing it from elementary gates. The first approach works in the decoherence-free subspaces (DFS) due to the quantum Zeno effect, which is robust against cavity decay. Based on the first model, we then propose the second approach which takes advantage of stimulated Raman adiabatic passage (STIRAP) with only six pulses; thus it is insensitive to the atomic spontaneous emission. The two schemes are suitable for different decoherence parameters. The strictly numerical simulation shows that the average gate fidelities for the two methods are relatively high.