Parametrically Activated Entangling Gates Using Transmon Qubits

We propose and implement a family of entangling qubit operations activated by radio-frequency flux pulses. By parametrically modulating the frequency of a tunable transmon, these operations selectively actuate resonant exchange of excitations with a statically coupled, but otherwise off-resonant, neighboring transmon. This direct exchange of excitations between qubits obviates the need for mediator qubits or resonator modes, and it allows for the full utilization of all qubits in a scalable architecture. Moreover, we are able to activate three highly-selective resonances, corresponding to two different classes of entangling gates that enable universal quantum computation: an iSWAP and a controlled-Z rotation. This selectivity is enabled by resonance conditions that depend both on frequency and amplitude, and is helpful in avoiding frequency crowding in a scalable architecture. We report average process fidelities of F = 0.93 for a 135 ns iSWAP, and F = 0.92 for 175 ns and 270 ns controlled-Z operations.