Efficient Generation of W Entangled States Among Superconducting Qubits via Lie-Algebra–Based Transforms

An efficient scheme is proposed to construct an evolution operator by using Lie-algebra–based transforms for generating tripartite and quadripartite W states among superconducting qubits. We consider four superconducting qubits coupled to a microwave cavity in the circuit quantum electrodynamics, where one plays the role of auxiliary qubit while the other three ones are systematic qubits. By adjusting the coupling strength between the qubits and the cavity, the complicated superconducting circuit system can be reduced to an effective system with three quantum states. Then by using Lie-algebra–based transforms, an evolution operator can be designed on the Hilbert subspace of the effective system, and further the time-dependent Rabi frequencies of external classical fields can be engineered to generate the tripartite and quadripartite W states.