Charting the design landscape of circuit QED for optimal gates

We map out the experimentally reachable design landscape of circuit QED in terms of achievable fidelity of universal gate sets for arbitrary perfectly entangling two-qubit gate. Using state-of-the-art control techniques, we exhaustively explore the landscape for creation and removal of entanglement, needed respectively for two- and single-qubit gates. Our approach is valid for both fixed- and tunable-frequency qubits, where in the tunable case a separation between points of a few 100MHz is allowed for different gates. We also compare to the case where the qubits are driven directly with dedicated lines. We find a system-wide global optimal regime in the parameter space where multiple transition paths destructively interfere so that net static coupling is suppressed but microwave-activated coupling can still attain high values. This regime allows for a significant speedup compared to using static coupling to entangle qubits, and over working in the usual strongly dispersive regime.