Has Google just announced quantum supremacy?

A paper from Google and NASA claims that the organisations have achieved quantum supremacy, prompting mixed reactions from the scientific and technological communities, before being taken down.

“To our knowledge, this experiment marks the first computation that can only be performed on a quantum processor. Quantum processors have thus reached the regime of quantum supremacy.”

This is one of the reported conclusions drawn in ‘Quantum Supremacy Using a Programmable Superconducting Processor’; a paper authored by Google, in collaboration with researchers at NASA, which appeared online briefly (and, we can assume, mistakenly) last week. Since then, the publication has been taken down, hopefully until the final version is ready.

From when the Financial Times broke the story, it didn’t take long for the mainstream media and both the scientific and technological communities to catch up, with articles appearing on Physics World, WIRED, VICE and The Economist to name but a few.

Response to this news has been mixed. Within hours, US Democratic candidate Andrew Yang was warning that Google’s quantum computers could break encryption, while others were questioning what the authors actually meant by the term ‘quantum supremacy’. Meanwhile, neither Google nor NASA were willing to comment.

Whether it meant to or not, this paper places ever-more focus on the world of quantum computing; its benefits and threats. In turn, this means that quantum-safe security is becoming more important than ever.

About the experiment

As described in the leaked paper, the first computational task the research team carried out to demonstrate quantum supremacy was to compare the quantum processor against classical computers in sampling the output of a random quantum circuit.

Rather than using Google’s 72-qubit ‘Bristlecone’ quantum chip, the researchers designed a smaller processor named Sycamore. While the processor originally consisted of 54 qubits, the experiment was carried out by only 53 of the quantum bits after one didn’t function properly.

As described in Physics World “The paper describes how a quantum computer comprising 53 programmable superconducting quantum bits was used to determine the output of a randomly-chosen quantum circuit made from a sequence of quantum gates. The output is a string of binary numbers and if the process is repeated many times, the results can be described as a probability distribution that resembles an interference pattern. This arises from the quantum interference that underlies the operation of quantum circuit.”

This pattern was determined by Sycamore making one million measurements on the quantum circuit, taking about 200 seconds. The authors say that a state-of-the-art (classical) supercomputer would require about 10,000 years to perform the equivalent task; leading to their claims of realising quantum supremacy.

What do we mean by quantum supremacy?

Quantum supremacy refers to the point at which a quantum computer can solve problems that are practically unsolvable by classical computers – i.e. the ability to solve them in a reasonable timeframe.

By this definition, it would indeed seem that Google and NASA have achieved quantum supremacy. After all, solving a 10,000 year classical computing problem in 200 seconds could be said to be a perfect illustration. However, this event only tells part of the story (namely the capabilities of the quantum processor, rather than its practical application), so perhaps it’s time to expand and add context to this definition.

While ground-breaking, the experiment itself was an illustration of quantum supremacy and not one that is going to trouble long-term cryptographic security in its current form. It is currently thought that a feat such as breaking RSA encryption can only be accomplished by a quantum computer with thousands of logical qubits. Current quantum processors all have fewer than 100 physical qubits, with an overhead of at least a factor 1000 to obtain a logical qubit. There is still work to do!

A milestone for deploying quantum-safe security

While the results of this experiment will not directly impact the cryptographic standards that underpin much of the modern economy, it once again highlights the risks of quantum computing to organisations. It also emphasises the importance of deploying quantum-safe security solutions, such as Quantum Random Number Generation (QRNG) and Quantum Key Distribution (QKD), sooner rather than later.

The paper is reported to address the growth of the computational powers of quantum computers, expecting them to grow at double the exponential rate. “As a result of these developments, quantum computing is transitioning from a research topic to a technology that unlocks new computational capabilities. We are only one creative algorithm away from valuable near-term applications.”

Find out more about IDQ’s quantum-safe security solutions.