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Google team reports magic-state cultivation on a superconducting chip
A Google Research preprint says cultivation on a Willow superconducting processor cut magic-state error about 40-fold, to fidelity 0.9999(1) while keeping 8% of attempts.
Google Research scientists report an experimental demonstration of magic-state cultivation on a superconducting Willow processor, saying the protocol reduced error about 40-fold relative to state injection and yielded a magic-state fidelity of 0.9999(1) while retaining 8% of attempts1.
The preprint was posted to arXiv as 2512.13908, with corresponding authors Emma Rosenfeld and Kevin J. Satzinger1.
Fault-tolerant quantum computers need non-Clifford gates, often supplied by high-fidelity “magic” states that are usually produced with costly distillation. Cultivation, a 2024–2025 theoretical proposal, instead uses fault-tolerant measurements and post-selection to refine a logical magic state so that fewer distillation rounds, or none, may be needed1.
The team injected a noisy |T> state into a distance-3 color code, refined it with phase-kickback measurements of the logical Hadamard, and discarded shots with detection events. They then grafted the state into a distance-5 surface code, a step they say prior theory work did not fully simulate at this scale1.
Using “kickback tomography” — extra cultivation and quantum-error-correction cycles as a measurement of the same axis — they report a full-circuit logical error of about 1×10−4 to 2×10−4 near |T>, an improvement of roughly 40 times versus injection without cultivation. About 8% of data remained after two extra cultivation rounds and three QEC cycles1.
The experiment used a 105-qubit Willow device with reinforcement-learning calibration to cut error-detection rates. The authors compare the fidelity to recent trapped-ion magic-state work and note superconducting circuits remain faster. They also report calibration drift over the course of data taking1.
The paper is a preprint and has not been peer-reviewed. Required infidelities for applications such as RSA-2048 factoring (~10^−10) remain far below this bound; cultivation is presented as a way to shrink, not yet replace, distillation for those targets1.
What is still unknown includes how well the protocol scales on larger codes, how grafting errors limit usable fidelity in a full factory, and whether independent groups will reproduce the result on other hardware1.
