Google's quantum chip Willow

 Hartmut Neven, Meet Willow, our state-of-the-art quantum chip, Google Research, Dec 09, 2024.

Willow has state-of-the-art performance across a number of metrics, enabling two major achievements.

• The first is that Willow can reduce errors exponentially as we scale up using more qubits. This cracks a key challenge in quantum error correction that the field has pursued for almost 30 years.
• Second, Willow performed a standard benchmark computation in under five minutes that would take one of today’s fastest supercomputers 10 septillion (that is, 10^25) years — a number that vastly exceeds the age of the Universe.

Quantum error correction: Really nice introduction

Quantum error correction (QEC) is a set of techniques used in quantum computing to protect quantum information from errors due to decoherence and other quantum noise. Quantum error correction is theorised as essential to achieve fault tolerant quantum computing that can reduce the effects of noise on stored quantum information, faulty quantum gates, faulty quantum state preparation, and faulty measurements. Effective quantum error correction would allow quantum computers with low qubit fidelity to execute algorithms of higher complexity or greater circuit depth.

Google Quantum AI and Collaborators. Quantum error correction below the surface code threshold. Nature (2024). https://doi.org/10.1038/s41586-024-08449-y  

We also make several improvements to decoding, employing two types of offline high-accuracy decoders. One is a neural network decoder [27], and the other is a harmonized ensemble [28] of correlated minimum-weight perfect matching decoders [29] augmented with matching synthesis [30]...

To quantify the impact of correlated errors along with more typical gate errors, we form an error budget....

Finally, we test sensitivity to drift. Finally, we test sensitivity to drift.

How could we use (distributionally) robust optimization to solve the above problems?