Generating and detecting multi-qubit GHz states in circuit QED
This is one of several projects which have as a common theme the measurement of qubits and resonators states for the purpose of developing new building blocks and protocols for quantum information processing.
The methodology involves taking a non-equilibrium open system approach to modeling and employing large scale computer simulations. Here we proposed a method for the preparation and entanglement detection of multi-qubit GHZ states in circuit quantum electrodynamics. Using quantum trajectory simulations appropriate for the situation of a weak continuous measurement, we showed that the joint dispersive readout of several qubits can be utilized for the probabilistic production of high-fidelity GHZ states. When employing a nonlinear filter on the recorded homodyne signal, the selected states are found to exhibit values of the Bell-Mermin operator exceeding 2 under realistic conditions. In order to motivate an experimental use of this method, we showed that with the use of dispersive readout it is in principle possible to demonstrate a violation of the Mermin bound.The figure shows the time evolution of several individual simulated quantum trajectories during the joint dispersive measurement.