Coupling qubits in circuit-QED cavities connected by a bridge qubit
Mun Dae Kim, Jaewan Kim · Physical Review A · 2016
We analyze a coupling scheme for qubits in different cavities of circuit-QED architecture. In contrast to the usual scheme where the cavities are coupled by an interface capacitance we employ a bridge qubit connecting cavities to mediate two-qubit coupling. This active-coupling scheme makes it possible to switch on or off and adjust the strength of qubit-qubit coupling, which is essential for scalability of quantum circuits. By transforming the Hamiltonian we obtain an exact expression of two-qubit coupling in the rotating-wave approximation. For the general case of $n$ qubits the Hamiltonian can produce the $W$ state as an eigenstate of the system. We calculate the decay rate of the coupled qubit-resonator system to find that it is viable in real experiments.