Demystifying science | Why a quantum computer?

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What is a quantum computer used for?
— Marie Pepin

In the medium term, to solve problems too complex for traditional computers. For example, they will make all current encryptions obsolete overnight. This could give an immense advantage to the country that first has this technology.

“These are machines that will serve very specific needs initially,” explains Claude Crépeau, specialist in the field at McGill University. “We have already identified four or five applications where a quantum computer will be much more efficient. And there should be more. »

In early March, Google launched a $5 million prize for demonstrations of other applications where quantum computing will be essential.

A traditional computer chip works by sending one of two messages: either a 0 or a 1. The quantum computer has a virtually infinite number of messages between this 0 and this 1, explains Mr. Crépeau. “It allows for much more complex calculations. »

This is why it will revolutionize cryptography.

Since this capacity of possible quantum computers was confirmed, 10 to 15 years ago, the great powers – China, Russia, United States, for example – copy everything that is posted on the Internet in order to be able to decode it when they will have this technology, according to Mr. Crépeau. “There is a certain urgency to change encryption systems. For around ten years, there has been a movement to replace them with new standards which will not be vulnerable. »

Current quantum computers are the equivalent of “toys,” according to Mr. Crépeau. “They work, but they have a memory and reliability that only allows them to perform around ten operations. They would have to be able to do 10,000 or 100,000 for it to be useful. What we know is that we will get there, within 5 years, 10 years, 20 years. »

Moore’s Law

In recent years, the miniaturization of traditional computer chips has reached limits close to the size of an atom. Thus, “Moore’s Law”, which predicted in 1965 that the number of transistors per chip would double every year, could soon be obsolete.

“We have reached distances of two nanometers between the components of a chip,” explains Delphine Bouilly, a physicist from the University of Montreal who works on the subject. “That’s the equivalent of five or six atoms. We cannot cut an atom in two. We can continue to progress with optimization, artificial intelligence and new materials, but there may be limits to increasing the power of current chips. »

For the moment, quantum chips are not intended to replace current chips, according to M^me Bouilly and Mr. Crépeau. But unlike the latter, quantum chips do not have this miniaturization limit and could therefore possibly take over.

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