Calibrating a 101 qubit processor operating below the surface code threshold

Quantum error correction provides a path to reach practical quantum computing by combining multiple physical qubits into a logical qubit, where the logical error rate is suppressed exponentially as more qubits are added. However, this exponential suppression only occurs if the physical error rate is below a critical threshold. In recent work, we demonstrated two surface code memories operating below this threshold [1]. The logical error rate of our larger quantum memory is suppressed by a factor of Λ = 2.14 ± 0.02 when increasing the code distance by two, culminating in a 101-qubit distance-7 code with 0.143% ± 0.003% error per cycle of error correction. Our results present device performance that, if scaled, could realize the operational requirements of large scale fault-tolerant quantum algorithms.

In this presentation, we will delve into various calibration aspects that went into achieving this level of performance, as well as discuss future challenges related to the scalability and stability of these systems.

[1] Quantum error correction below the surface code threshold, Google Quantum AI, arXiv:2408.13687 (2024)