Fast, High-Fidelity Conditional-Phase Gate Exploiting Leakage Interference in Weakly Anharmonic Superconducting Qubits

• Published in: Physical review letters Vol. 123; no. 12; pp. 1 - 120502
• Main Authors: Rol, M. A., Battistel, F., Malinowski, F. K., Bultink, C. C., Tarasinski, B. M., Vollmer, R., Haider, N., Muthusubramanian, N., Bruno, A., Terhal, B. M., DiCarlo, L.
• Format: Journal Article
• Language: English
• Published: College Park American Physical Society 18-09-2019
• Subjects: Accuracy; Anharmonicity; Computer simulation; Distortion; Flux; Harnesses; Interference; Leakage; Robustness (mathematics); Time
• ISSN: 0031-9007; 1079-7114
• DOI: 10.1103/PhysRevLett.123.120502

Conditional-phase (cz) gates in transmons can be realized by flux pulsing computational states towards resonance with noncomputational ones. We present a 40 ns cz gate based on a bipolar flux pulse suppressing leakage (0.1%) by interference and approaching the speed limit set by exchange coupling. This pulse harnesses a built-in echo to enhance fidelity (99.1%) and is robust to long-timescale distortion in the flux-control line, ensuring repeatability. Numerical simulations matching experiment show that fidelity is limited by high-frequency dephasing and leakage by short-timescale distortion.