New preprint “Optimizing Superconducting Three-Qubit Gates for Surface-Code Error Correction” and parallel preprint released
A new pre-print by Stephan Tasler, Josias Old, Lukas Heunisch, Verena Feulner, Timo Eckstein, Markus Müller, and Michael J. Hartmann has been published on the arXiv.
It addresses quantum error correction (QEC), which is a crucial element for fault tolerant quantum computation. Prominent QEC codes are stabilizer codes, for which the stabilizer operators are read out by successive two-qubit gates. To improve the QEC cycle, three-qubit gates can be used to measure the stabilizer operators. Yet, such multi-qubit gates can create fault-tolerance breaking errors and thus destroy the efficiency of the QEC code. In this work, the authors systematically suppress fault-tolerance-breaking Pauli errors by optimizing the three qubit gates accordingly. In the experimentally relevant regime, they find, for the rotated surface code, that the error threshold increases by nearly 50% to ≈ 1.2% and the logical error rate decreases compared to the two-qubit gate scheme, although the readout schedule is not strictly fault tolerant.
In a parallel paper, out on the same day, and also on the arXiv, the authors Josias Old, Stephan Tasler, Michael J. Hartmann, and Markus Müller show that, for the unrotated surface code, a strictly fault-tolerant readout schedule can be found using three-qubit gates.