The coldest computers in the world

The coldest computers in the world

Strathclyde University Neutral Atom Experiment

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Jack Hao Yang

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Scientists are capturing atoms and slowing them down

Imagine the United States is under attack. An enemy plane, loaded with warheads, is heading towards the coast, entering and exiting the radar. The fighter planes have been scrambled and there is a frantic effort to locate the target.

But the nation’s best defense is not an aircraft carrier or a missile system. It’s a box of incredibly cold atoms.

“Use the quantum computer,” shouts a general. The atoms inside the computer can solve complex problems and, almost instantly, spit out instructions on how to reconfigure a radar array so that the enemy aircraft can be tracked and targeted.

A company already grappling with a scenario like this is ColdQuanta. It recently signed a contract with US defense research agency Darpa to build a quantum computer that can quickly work out the best way to reposition radar equipment in the event of a partial failure of a defense system.

The project is based on the ability to collect a sufficient number of atoms as qubits, the building blocks of a quantum computer, which allow it to perform calculations.

To do this, the atoms must be extremely cold, making such computers the coldest in the world.

Quantum computing is highly publicized, but the technology is in its infancy. Companies are just starting to build systems that claim they will someday surpass traditional digital computers in certain useful tasks.

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Quantum computing is still in its experimental stage

“What we are being asked to do in the next 40 months is to have a machine with thousands of qubits to solve a real defense problem and what we are working on is a version of this radar coverage problem,” explains Bo Ewald. , chief executive officer of ColdQuanta, based in Colorado.

The example above is an optimization problem, a scenario for which there may be thousands or millions of possible solutions. The key is to choose the best.

In addition to military applications, quantum computers could have uses in drug design, investment strategies, cryptographic cracking, and complex planning problems for large fleets of vehicles.

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Mr. Ewald says this is where quantum computers will have their initial impact: finding optimal solutions to problems that would take existing computers, even the fastest supercomputers, many hours or days to fix.

There are various types of quantum computers under development, but the approach using ultra-cold neutral atoms such as qubits is unusual: it is different from superconducting quantum computers developed by large companies like IBM and Google, or other projects that also use charged atoms. . known as ions instead.

Superconducting quantum computers do not use single atoms as qubits, and although these systems rely on low temperatures, they are not as low as those needed for ColdQuanta’s neutral atoms.

“The superconductors are running to millikelvin … we are down to microkelvin,” he explains proudly.

Kelvin is a measure of temperature. Zero kelvin, absolute zero (-273.15 ° C) is as cold as it can ever be.

And while millikelvin is cold, at 0.001 kelvin, ColdQuanta’s microkelvin atoms are much cooler – at around 0.000001 kelvins. Both are significantly colder, in fact, than anywhere else in the natural universe.

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The atoms are trapped in a glass box by the lasers

In the case of ColdQuanta the rubidium atoms are gathered together inside a vacuum inside a tiny hexagonal or rectangular glass box, about one inch wide, one inch deep and two inches high. The atoms are held aloft exclusively by lasers.

But why is temperature so important? Prof Andrew Daley of the University of Strathclyde says it is crucial to be able to manipulate atoms and hold them in place.

Shining lasers on atoms prompts them to release some energy and slow down. This makes it possible to keep them almost perfectly still, which is the real point here. They are not cold in the sense that you or I would conceive of cold – rather, they are just noticeably slowed down.

Once you have your ducks – atoms – lined up, you can arrange them however you want, says Prof Daley. This fine-grained control over atoms means they can be placed in two-dimensional or three-dimensional formations, clustered next to each other in the heart of a quantum computer. This is important because with each additional atom, the computer’s capabilities are doubled.

Hitting each neutral atom with another laser excites them, greatly increasing their size. These adjustments encode information or connect atoms through a strange phenomenon called entanglement. You now have a collection of qubits that work together as a system that you can modify to represent a mathematical model or problem of some kind.

Surprisingly, the user of a quantum computer could theoretically program this system to simulate a huge number of possibilities at once. It’s not quite like a traditional computer processing a lot of calculations in parallel, it’s stranger and less predictable than that, and getting a useful answer in the end is tricky.

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Andrew Daley

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Professor Daley is waiting for quantum computers to perform a “useful” task

“What you want is that the quantum state ultimately represents the answer to the problem you are trying to solve,” says Jonathan Pritchard, a colleague of Prof Daley at Strathclyde. The quantum computer should end up favoring a particular state, or a particular answer to a problem.

For the right problem, it could bring us much closer to an optimal response, both more quickly and efficiently, than a traditional computer.

“We are still waiting for a demonstration of a compute business where we can demonstrate that these machines have done something beyond what is possible on a classic computer, for something that is actually useful,” says Prof Daley.

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Bamdad Norouzian

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Quantum computing takes advantage of the strange interaction of atoms

The French company Pasqal is building a prototype system, based on principles similar to ColdQuanta.

Pasqal’s system is for energy giant EDF, which, if it works, will provide super-efficient programs for charging electric vehicles. Specifically, the goal is to minimize the total time it takes to complete recharging for all vehicles, while also prioritizing some more important vehicles over others.

This type of problem could be addressed by a traditional computer, admits Christophe Jurczak, president, but argues that a quantum system will end up being significantly faster, say in one hour rather than 24 hours.

“It doesn’t look that big, but if you want to update your strategy every hour, it’s a big difference,” he says. And it could use 100 times less electricity than a supercomputer in the process.

At the moment, this all remains to be demonstrated for real. But there are signs that in the next few years – faster than some expected – we will discover just how useful this incredibly cold breed of computers is.

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