Why is Google's quantum victory a huge deal and a disappointment?

They finally did it. After years – no, decades – of declarations of hope and dreams without concrete results, researchers in the quantum computing community have kept their promises. Where do they come from?

Last week, it was revealed that researchers at Google and other institutions had solved a problem on a quantum computer 1 billion times faster than a conventional computer. Google did not respond to a request for comment, but according to a manuscript project describing the experiment, they achieved "quantum supremacy", a feat that "heralds the advent of". a highly anticipated computer paradigm ".

The reactions of the rest of the quantum community, however, have been downright contradictory. In an email, physicist John Preskill of Caltech called the work "a truly impressive achievement in experimental physics". Cautions that the leaked manuscript is only a rough draft, the University of Bristol mathematician Ashley Montanaro said it was "all of a sudden." really exciting. " Dario Gil, director of research at IBM, challenges the very notion of quantum supremacy, calling the term "misleading" in a statement to WIRED.

So which one is true? Has the Google team just crossed a steep technological threshold or has it achieved a virtually useless experience dressed in a smart brand strategy? The truth lies somewhere in between and captures the competing tensions in the world of quantum computing.

On the one hand, these researchers have managed to achieve an extremely complex experiment built on tedious mathematical proofs and years of material development – an undeniable achievement. However, the experiment does not bring them closer to the profitable applications promised by the quantum community, in which the unique capabilities of the computer calculator will reveal new molecules for better batteries, better drugs, etc., at a speed that would make you ashamed classic computers. It's both a major victory and a bit disappointing.

To understand this, let's describe what the Google document actually describes. The researchers conducted the experiment on a quantum computer chip called Sycamore, which contains 54 tiny objects called qubits that they can program to represent the digit 0, 1 or a weighted combination of the two, called superposition. Researchers apply voltage pulses and microwaves to qubits according to different sequences, modifying their values ​​according to the rules defined by quantum mechanics. Chain multiple pulse sequences and you have written an algorithm for a quantum computer.

In the experience of quantum supremacy, Google scientists have designed pulse sequences that essentially turn their computer into a random number generator. They then made the quantum computer spit out millions of numbers. Although the figures seem random, they are nevertheless supposed to conform to the model prescribed by Google's algorithm. So they then checked to see if the numbers were obeying this distribution. They did it.

This task alone is essentially an excuse for a quantum computer and a supercomputer. Its practical implications are minimal. But this is the first race that a quantum computer seems to have won. The supercomputer could not verify that the numbers were obeying the distribution over time.

The scientific effort behind this experiment began more than a decade ago, with researchers outside of Google. In 2004, Barbara Terhal and David DiVincenzo, then at IBM, developed the initial mathematical proof that qubits could compute this specific task faster than conventional bits. It was not obvious that anyone would try to accomplish this task; capable quantum computers did not even exist yet.

"I thought it was a good idea, but a largely theoretical idea," says Terhal, who is now working at the Delft University of Technology in the Netherlands. "We submitted an initial version to a computer conference and it was rejected. It was not like "Oh, it's a good idea!" Not at all. "