Entanglement of superconducting charge qubits by homodyne measurement

We present a scheme by which projective homodyne measurement of a microwave resonator can be used to generate entanglement between two superconducting charge qubits coupled to this resonator. The non-interacting qubits are initialized in a product of their ground states, the resonator is initialized in a coherent field state, and the state of the system is allowed to evolve under a rotating wave Hamiltonian. Making a homodyne measurement on the resonator at a given time projects the qubits into a state of the form (vertical bar gg > + e(-i phi)vertical bar ee >)/root 2. This protocol can produce states with a fidelity as high as required, with a probability approaching 0.5. Although the system described is one that can be used to display revival in the qubit oscillations, we show that the entanglement procedure works at much shorter timescales.