Abstract

Photonic systems are promising for realizing quantum information processing because of their long coherence times. However, due to the weak interaction between photons, implementation of photon-photon gates has been difficult. One way to overcome this problem is to exchange the photonic qubits and the atomic qubits and to enhance the interaction using the cavity QED systems or the waveguide QED systems [1-3], where the spatial modes of the input photon and the radiation from the atom match in a one-dimensional field and strongly interfere with each other. A pioneering work in this direction is Duan-Kimble scheme [1,4], which achieves a controlled-NOT gate between photons with active control of the atom such as initialization, single-qubit rotation, and measurements. Recently, we showed that deterministic swapping of photonic and atomic qubits is possible by using a Λ-type atom and proposed a scheme for $\sqrt{\text{SWAP}}$ gate between photonic polarization qubits [2]. An advantage of this scheme is that the atom is used totally passively, that is, active control of the atom is unnecessary throughout the gate operation. However, the scheme requires photonic qubits with different frequencies, which makes the scheme inconvenient practically.

© 2015 IEEE