Mitigating spectator effects in multi-transmon quantum processors with tunable couplers

The integration of flux-tunable couplers into multi-transmon quantum processors has proven the ability to null ZZ interactions, reducing phase errors and leakage caused by inactive (i.e., spectator) transmons during two-qubit gates. However, for the commonly used multi-path coupler design, the nulling of ZZ interactions requires transmons to lie in the so-called straddling regime, with qubit transition frequencies separated by less than one anharmonicity. At these reduced detunings, remaining exchange couplings can introduce significant spectator-induced errors in single-qubit gates and readout. In this talk, we present choices in device architecture and approaches to static and dynamic flux pulsing to simultaneously achieve high fidelity in single-qubit gates, two-qubit gates, and readout in 5- to 17-transmon processors. In particular, our implementation of Controlled-Z (CZ) gates without flux pulses on transmons maximizes their coherence and minimizes their interaction with two-level defects and spectators. We use detailed numerical simulations to understand the limits of this CZ realization. We quantify system-level performance using multi-qubit benchmarks combining the three types of operations and present latest efforts in quantum error correction with this architecture.