Quantum computing is the kind of technology that is hard to beat, with the potential to perform calculations in a single step that would take a traditional computer hundreds of thousands of years.

The problem is that the same loophole in physics that gives quantum computing its incredible power also makes it nearly impossible to control reliably — but researchers say this is about to change, and large-scale quantum chips that could finally deliver on the promise of quantum computing. could be here much earlier than we expected.

New research published in scientific progress on Aug. 13, claims a new technique could provide quantum computing engineers with a way to control not just tens or a few hundred qubits, but millions, removing one of the biggest hurdles that prevented quantum computing from being commercially practical.

Credit: Walden Kirsch/Intel Corporation
The problem with qubits is that they depend on a phenomenon in quantum mechanics known as: superposition , which allows a subatomic particle to have two mutually exclusive properties at the same time (such as the spin of an electron).

Quantum computing engineers use this superposition to represent the ones and zeros that are the foundation of digital technology — the bit — but because of superposition, a qubit can be both one and zero at the same time (making it a quantum bit, or qubit for short). ).

This allows a quantum computer to perform unfathomably complex calculations that would take an Intel Rocket Lake processor a billion years to perform in one go by calculating all possible results. at the same time .

The problem is that the moment you “look” at a qubit, the superposition collapses to a defined state and it just becomes a plain old bit and the incredible computing power of qubits is lost.

This makes effective control over them to perform calculations incredibly difficult, requiring all sorts of equipment to block out outside interference and keep the qubits as close to absolute zero as possible, keeping them mostly still and not crashing into each other, which all counts as “looking” in terms of quantum mechanics.

(Image credit: Quantum Motion)
This has paralyzed engineers who have struggled to reliably control tens, hundreds, or at most a few thousand qubits, but now researchers at the University of New South Wales (UNSW) say they have solved the problem of qubit control. potentially unlocking the power of quantum computing for our most pressing real-world problems, such as medical research, climate forecasting, and more.

“Until now, the control of electron spin qubits relied on providing microwave magnetic fields by passing a current through a wire right next to the qubit,” said Dr. Jarryd Pla, a faculty member at the UNSW School of Electrical Engineering and Telecommunications. “This poses some real challenges if we are to scale to the millions of qubits a quantum computer needs to solve important problems worldwide, such as the design of new vaccines.”

The problem is that to add more qubits, you have to add more wires to generate the magnetic field needed to control them. However, wires generate heat, and too much heat can cause qubits to collapse into pieces, so throwing more wires into a quantum processor just won’t work.

The researcher’s solution to this problem was to completely remove the wires and apply the magnetic control fields from above the quantum chip using a crystal prism called a dielectric resonator, which allows you to control all qubits simultaneously.

“First we removed the wire next to the qubits and then devised a new way to deliver microwave-frequency magnetic control fields across the entire system,” said Dr. Pla. “So basically we could provide control fields up to four million qubits.”

Making large-scale quantum computing a reality
“I was completely blown away when [Dr. Pla] came to me with his new idea,” said Prof. Andrew Dzurak, a technical colleague of Dr. Pla’s at UNSW, who had spent years implementing quantum logic on silicon chips. “We immediately got to work to see how we could integrate it with the qubit chips my team has developed.”

“We were overjoyed when the experiment turned out to be successful,” he added. “This problem of how to control millions of qubits has worried me for a long time, because it was a major roadblock to building a full quantum computer.”

While this research may prove to be a crucial step towards widespread, large-scale quantum computing, there is still a lot of work to be done. One of the challenges to overcome is that while a quantum computer can calculate as many results as the number of qubits allows, actually reading the desired response from those same qubits causes the same quantum decoherence as heat or other interference. So even though a quantum computer has calculated every possible result, in the end you only have one access to it.

“The trick is to design your algorithm so smartly that the correct answer you’re looking for shows up at the end of the calculation, still using the parallelism,” Dr. Placing via email to Ditching. “That’s why a quantum computer can only perform certain tasks faster [than classical computers] (such as factoring large composite primes, searching unsorted databases, etc.), because it is difficult to design such smart algorithms – although people are getting better at this and more useful examples appear almost daily.”

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Other technical challenges also need to be addressed, such as refining error correction so that it doesn’t take as many qubits to build quantum circuits.

“It’s very important to tell the difference between a ‘physical qubit’ (ie, in our case, a single electron spin) and a ‘logical qubit,'” Dr. Place us. “If all your physical qubits could be monitored and measured with infinite precision (no errors at all), you’d have a quantum computer of 4 million qubits that could solve just about any problem we can think of right now.

“However, qubits have errors and these errors grow very quickly in a quantum circuit. So you have to implement some form of error correction where qubits are encoded into groups of qubits (this is called quantum error correction). The error protected qubit groups become logical called qubits How many qubits you need in the groups depends a lot on the system, ie how well the qubits are interconnected and the actual error rates.

“So, for example, we need somewhere on the order of 1000 physical qubits to produce a usable logical qubit that can be used in calculations. This brings the count down from 4 million to 4000 – which is still very useful. level, you can break 2048-bit number encodings and simulate complicated chemical processes, elucidate protein structures, etc.”

Well, it’s a start, and we wouldn’t have the modern information age without producing the room size first ENIAC , but hopefully we won’t have to wait long to see the potential of quantum computers become a reality.