Google says it has achieved “quantum computational supremacy”

In a new study published this week, engineers at Google claim they’re the first to achieve “quantum computational supremacy.” The mythical-sounding term describes crossing the threshold where quantum computers can do things that conventional computers cannot.


The qubit circuits of Google’s quantum computer Sycamore. Credit: Google.

It’s difficult to grasp just how quantum computers work, but if we were to simplify things, the gist would be that digital computers require data to be encoded into binary digits (bits), each of which is always in one of two definite states (0 or 1), whereas quantum computers use qubits, also known as quantum bits.

A qubit is the quantum analog of the digital bit that encodes information in 1s and 0s. The crucial difference is that a quantum bit can exist in both states at the same time due to a quantum quirk called superposition.

It’s akin to saying that a switch is both on and off at the same time or that water is both flowing and not flowing through a pipe simultaneously — which, in day to day life, makes absolutely no sense, but in the quantum domain, few things are reasonable.

Two-qubits can perform operations on four values, three on eight values and so on in powers of two. Today’s computers have millions of transistors. Now imagine a quantum logic gate that works with millions of qubits. The computing force would be unheard of.

The field is still in its infancy but experiments have been carried out where quantum computational operations were executed on a very small number of qubits. The problem is designing a quantum computer for which qubits don’t fail due to decoherence caused by vibrations, temperature fluctuations, electromagnetic waves and other interactions with the outside environment, which ultimately destroys the exotic quantum properties of the computer.

In a new paper, Google researchers have announced a huge breakthrough. They claim that their 54-qubit quantum processor, known as Sycamore, was able to solve a random-number generation problem within 200 seconds, whereas a normal machine would have taken 10,000 years.

“This demonstration of quantum supremacy over today’s leading classical algorithms on the world’s leading supercomputers is truly a remarkable achievement,” William Oliver, a computer researcher at the Massachusetts Institute of Technology, wrote in a comment piece on the discovery. Oliver said that this discovery is on the same level as the first manned flight taken by the Wright Brothers at the beginning of the 20th Century.

“Their aeroplane wasn’t the first airborne vehicle to fly and it didn’t solve any pressing transport problem,” Oliver wrote.

“It is what the event represented, rather than what it practically accomplished that was paramount. And so it is with this first report of quantum computational supremacy.”

There are also critics who have voiced skepticism. Researchers at IBM, which has its own advanced quantum computing division, said that Sycamore’s performance have been overhyped. IBM’s own calculations suggest that an ordinary computer would take about 2.5 years to match Sycamore’s feats rather than 10,000 as claimed by Google. As such, they say, Google’s claims are totally exaggerated.

“Because the original meaning of the term ‘quantum supremacy’… was to describe the point where quantum computers can do things that classical computers can’t, this threshold has not been met,” they wrote

Another thing to work on is that this machine, although very impressive, is still a long away from being practical. Sycamore still generates errors and, to correct them, the quantum computer would have to encode a single, more stable qubit (the “logical” qubit) in several less reliable qubits (the “physical” qubits) — this would enable the machine to maintain quantum states for longer times.

Google’s 76 authors who published the new study, however, are very optimistic. “We are only one creative algorithm away from valuable near-term applications,” they wrote.

The findings appeared in the journal Nature.

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