What just happened? In 2019, Google's Sycamore quantum computer achieved a so-called quantum supremacy record by completing a specific task in 200 seconds that would have taken a classical supercomputer 10,000 years to finish. There was a bit of controversy around this achievement, but by and large, Google's claim has withstood the test of time – until now. Last month, a company called Quantinuum said it reached an error correction performance threshold that many believed was years away.
A new 56-qubit H2-1 computer has dislodged Google's Sycamore quantum computer from its 'quantum supremacy' record by 100-fold.
That title now belongs to a computing company called Quantinuum, which ran multiple experiments on its quantum computer between January and June 2024. It claims that its machine hit an error correction performance threshold that many experts believed was still years away.
The company published its results last month in a study uploaded to the preprint database arXiv. The study has not been peer-reviewed yet.
Quantinuum maintains that it has demonstrated a significant performance improvement using the Random Circuit Sampling algorithm. It achieved an estimated linear cross entropy benchmark (XEB) score of ~0.35, over 100 times better than previous demonstrations.
According to Quantinuum, the H2-1 configured with 32 physical qubits supported the creation of four highly reliable logical qubits operating at "better than break-even" – representing a major step towards fault-tolerant quantum computing. This means the logical qubits are more reliable than the physical qubits they're composed of, which is a crucial threshold for practical quantum error correction.
Also, the logical circuit error rates were shown to be up to 800x lower than the corresponding physical circuit error rates, which, Quantinuum said, no other quantum computing company has come even close to matching.
Error correction allows quantum computers to perform longer and more complex calculations by protecting quantum information from noise and decoherence. In quantum computing, error rates are typically much higher than in classical computing; current state-of-the-art quantum computers exhibit error rates ranging from 1% to 0.1%.
Google's Sycamore quantum computer features 53 qubits and was first introduced in 2019 when it completed a specific task in 200 seconds, registering an XEB result of approximately 0.002. Google claimed it would have taken the world's most advanced classical supercomputer, Summit, approximately 10,000 years to finish the task.
It achieved, in short, a significant milestone in quantum computing known as quantum supremacy. Later, IBM argued that the task would only take 2.5 days on a classical system like Summit.
But Ilyas Khan, founder and Chief Product Officer of Quantinuum, appears to accept Sycamore's achievement. "When, in late 2019, Google released details of their 'quantum supremacy' experiment, Sundar Pichai their CEO published a blog that has withstood the test of time with respect to the importance of the milestone that was then reached," he said.
Quantinuum's work "elevates that bar to one where we clearly now operate in a place that has been anticipated for so long. One where classical supercomputers simply cannot compete and where the computational task is measurable and relevant."