Parametrically Activated Entangling Gates Using Transmon Qubits

We describe and implement a family of entangling gates activated by radio-frequency flux modulation applied to a tunable transmon that is statically coupled to a neighboring transmon. The effect of this modulation is the resonant exchange of photons directly between levels of the two-transmon system, obviating the need for mediating qubits or resonator modes and allowing for the full utilization of all qubits in a scalable architecture. The resonance condition is selective in both the frequency and amplitude of modulation and thus alleviates frequency crowding. We demonstrate the use of three such resonances to produce entangling gates that enable universal quantum computation: one iSWAP gate and two distinct controlled-Z gates. We report interleaved randomized benchmarking results indicating gate error rates of 6% for the iSWAP (duration 135 ns) and 9% for the controlled-Z gates (durations 175 and 270 ns), limited largely by qubit coherence.