Demonstration of a High-Fidelity CNOT Gate for Fixed-Frequency Transmons with Engineered ZZ Suppression

Improving two-qubit gate performance and suppressing cross talk are major, but often competing, challenges to achieving scalable quantum computation. In particular, increasing the coupling to realize faster gates has been intrinsically linked to enhanced cross talk due to unwanted two-qubit terms in the Hamiltonian. Here, we demonstrate a novel coupling architecture for transmon qubits that circumvents the standard relationship between desired and undesired interaction rates. Using two fixed frequency coupling elements to tune the dressed level spacings, we demonstrate an intrinsic suppression of the static ZZ while maintaining large effective coupling rates. Our architecture reveals no observable degradation of qubit coherence (T-1, T-2 > 100 mu s) and, over a factor of 6 improvement in the ratio of desired to undesired coupling. Using the cross-resonance interaction, we demonstrate a 180 ns single-pulse controlled NOT (CNOT) gate, and measure a CNOT fidelity of 99.77(2)% from interleaved randomized benchmarking.

Automated summary

This study introduces a novel coupling architecture for transmon qubits that improves two-qubit gate performance and suppresses cross talk; by using two fixed frequency coupling elements, it achieves intrinsic suppression of static ZZ while maintaining large effective coupling rates; through cross-resonance interaction, a 180 ns single-pulse controlled NOT (CNOT) gate with a fidelity of 99.77% is demonstrated.