Willow: Crossing the threshold

“Subthreshold” operation has been a goal of error-corrected quantum computing since its introduction in the 1990s. But after nearly 30 years of progress in device manufacturing, calibration, and qubit design, quantum computers have still not passed this milestone. That is, until our latest 105-qubit superconducting processor Willow.

Willow represents a significant advance in quantum hardware. It maintains the tunability of our previous architecture, Sycamore, while improving the average qubit lifetime (T₁) from about 20 µs to 68 µs ± 13 µs. The qubits and operations in our device are optimized for quantum error correction and run alongside our error correction software, including state-of-the-art machine learning and graph-based algorithms to accurately identify and correct errors.

Using Willow, we report the first demonstration of exponential error suppression as surface code size increases. Every time we increase the size of our grid from 3×3 to 5×5 to 7×7, the encoded error rate drops by a factor of 2.14. This culminates in a logical qubit whose lifetime is more than twice that of its best physical qubit component, demonstrating the ability of an error-corrected qubit to go beyond its physical components.