Willow: beating the threshold
Operating “below the threshold” has been a goal for error corrected quantum computing since its inception in the 1990s. However, after almost 30 years of advancement in device fabrication, calibration, and qubit design, quantum computers still hadn’t passed this landmark. That is, until our latest 105-qubit superconducting processor, Willow.
Willow represents a significant leap forward in quantum hardware. It maintains the tunability of our previous architecture, Sycamore, while improving the average qubit lifetimes (T1) from about 20 μs to 68 µs ± 13 µs. The qubits and operations in our device are optimized with quantum error correction in mind, and run alongside our error correction software, including state-of-the-art machine learning, reinforcement learning, and graph-based algorithms to identify and correct errors accurately.
Using Willow, we report the first ever demonstration of exponential error suppression with increasing surface code size. Each time we increase our lattice in size from 3×3 to 5×5 to 7×7, the encoded error rate decreases by a factor of 2.14. This culminates in a logical qubit whose lifetime is more than twice that of its best constituent physical qubit, demonstrating the capacity of an error-corrected qubit to go beyond its physical components.