Proposal for generating and detecting multi-qubit GHZ states in circuit QED

We propose methods for the preparation and entanglement detectionof multi-qubit Greenberger–Horne–Zeilinger (GHZ) states in circuit quantumelectrodynamics. Using quantum trajectory simulations appropriate for thesituation of a weak continuous measurement, we show that the joint dispersivereadout of several qubits can be utilized for the probabilistic production ofhigh-fidelity GHZ states. When employing a nonlinear filter on the recordedhomodyne signal, the selected states are found to exhibit values of theBell–Mermin operator exceeding 2 under realistic conditions. We discuss thepotential of the dispersive readout to demonstrate a violation of the Merminbound, and present a measurement scheme avoiding the necessity for fulldetector tomography