Entangling gates at dynamical sweet spots. Part 2: Experiment.

Current superconducting quantum processors require methods of performing two-qubit entangling operations that are robust to material defects and imperfect parameter targeting. Known techniques for achieving high fidelity gates include modulation of magnetic flux to control tunable transmon frequencies and activate sideband interactions between capacitively-coupled neighbors. However, viable operating points for these gates have historically been limited to specific modulation amplitudes at which there is first-order protection against dephasing due to 1 / f flux noise. As a result, there is little freedom to select time-averaged detunings that avoid unintended frequency collisions. This restriction can be relaxed, however, by introducing a second flux modulation frequency [1]. We show that by varying the mixing parameters and frequency relationship of the two tones, we can use these bichromatic pulses to maintain qubit insensitivity to flux noise across a wide continuum of effective frequencies, greatly improving the gate scheme’s robustness to defects and gate collisions. The presentation will review experimental results achieved via this novel control technique.

[1] N. Didier, Flux control of superconducting qubits at dynamical sweet spots, arXiv:1912.09416v1 (2019).