Quantum computation and entangled state generation via long-range off-resonant Raman coupling

A scheme is proposed to implement two-qubit controlled quantum phase gate and SWAP gate and generate two-qubit entangled state via long-range off-resonant Raman coupling between two spatially separated superconducting quantum-interference devices (SQUIDs). In the scheme each SQUID is coupled with a single-mode cavity individually and the two distant cavities are connected by an optical fiber. The two lowest levels of each SQUID are used to represent the two logical states of a qubit while the two intermediate levels of each SQUID are used to facilitate coherent coupling of quantum states of the qubits during the virtual excitation process of photon. The scheme is robust against fiber loss, cavity decay, and the effect of spontaneous decay from the higher levels and it would be an important step toward distributed quantum computation and long-distance entanglement distribution.