Fast two-qubit gates can be realized using frequency-tunable transmons as nonlinear coupling elements between two superconducting qubits [1-4]. The interaction between the two qubits is controlled by tuning the frequency of the coupling transmon with flux pulses. This gating scheme allows for high-fidelity iSWAP and CZ gates while increasing the hardware overhead and the complexity of the calibration procedure. In this work, we experimentally demonstrate that the interaction between two qubits can be controlled by applying a microwave drive to the coupler rather than flux pulses. For a particular qubit frequency, the interaction is turned off when the coupler is in its ground state while high coupling rate is achieved when the coupler is excited. We can perform an iSWAP gate by applying a resonant two-pi pulse on the coupler to maximize the population transfer between qubits while minimizing leakage to non-computational states. Our coupling scheme could significantly reduce the complexity of superconducting quantum processors by eliminating the need for coupler flux tuning lines.

[1] Li et al., Phys. Rev. Applied 14, 024070 (2020)
[2] Foxen et al., PRL 125 120504 (2020)
[3] Collodo et al., PRL 125 240502 (2020)
[4] Sung et al., PRX 11 021058 (2021)

This is joint work with G. Ethier-Majcher, C. Archambault, M. Wu, F. Aydinoglu, Y. Li and A. Najafi-Yazdi