Automatic characterization and calibration of a superconducting quantum processor capable of error correction.

Victor Negîrneac

Key information

Authors:

Victor Negîrneac (Victor Negîrneac)

Supervisors:

Pedro José Gonçalves Ribeiro (Pedro José Gonçalves Ribeiro); Leonardo DiCarlo

Published in

January 15, 2021

Abstract

Simple tuneup of two-qubit gates is essential for the scaling of quantum processors. In this work two key two-qubit gate calibration routines for flux-tunable transmon qubits were automated. Custom adaptive samplers were implemented to speed up measurements, along with analysis routines to process and visualize results. The sudden variant (SNZ) of the Net-Zero scheme was introduced realizing (two-qubit) controlled-Z (CZ) gates by baseband flux control of transmon frequency. The SNZ CZ gates operate at the speed limit of the transverse coupling between a computational and a non-computational state by maximizing intermediate leakage to the latter. The key advantage of the SNZ is tuneup simplicity, owing to the regular structure of conditional phase and leakage as a function of two control parameters. SNZ CZ gates were realized in a four-transmon patch, matching the state of the art on the best pair with fidelity of 99.93% [99.54+-0.27% average] and leakage of 0.10% [0.18+-0.04% average]. The SNZ is compatible with scalable schemes for quantum error correction and adaptable to generalized conditional-phase (CPHASE) gates useful in intermediate-scale applications. Taking advantage of the tuning simplicity, SNZ CZ gates are already employed in a quantum processor publicly available via the QuTech Quantum Inspire platform.