Parametric-resonance entangling gates for superconducting qubits

We demonstrate experimentally parametric resonance iSWAP and controlled-Z entangling gates via radio-frequency flux modulation of one of the qubits. In contrast to the standard parametric gates where sideband frequencies are used to activate the gates, parametric-resonance gates are activated when the average frequency of the modulated qubit is in resonance with the unmodulated qubit. This allows us to approximately retain the bare qubit-qubit coupling, as opposed to a reduction by 30% at best in the case of standard parametric gates. We show that fast high fidelity iSWAP and CZ gates can be realized by leveraging the flexibility of parametric modulation while maintaining the bare coupling rates. Moreover, because the modulation frequency is not used to activate the interaction, parametric-resonance gates provide flexibility in avoiding collisions with unwanted resonances. Finally, these entangling gates are protected from slow flux noise by operating the modulated qubit at a dynamical sweet spot