A research team with Denmark's University of Copenhagen has designed the world's first quantum computing system (opens in new tab) that allows for simultaneous operation of all its qubits without threatening quantum coherence. The research is being hailed as a breakthrough, clearing one of the remaining key obstacles for quantum scaling and its eventual mainstream deployment.
As quantum computing is still in its nascent stages, there are a number of technologies — and qubit types — concurrently being explored. The Danish team achieved its breakthrough in one particular type of qubit, spin qubits. You may remember these from our recent article on quantum benchmarks, where a company that is also employing the spin qubit approach, IonQ, achieved remarkable results compared to other systems.
"To get more powerful quantum processors, we have to not only increase the number of qubits, but also the number of simultaneous operations, which is exactly what we did," states Professor Kuemmeth, who directed the research.
As it stands, two important elements on the road to quantum computing are scaling, as in, adding more and more qubits (think computer cores) so that the system's processing capabilities increase; and coherence, as in, how stable the system is during workload processing, and how accurate its results are. With quantum scaling well on its way already, this research focuses on the coherence part of the equation. The scaling part of the problem has already seen incredible progress, but the same hasn't been true about the coherence part of the equation — until now.
"Now that we have some pretty good qubits, the name of the game is connecting them in circuits which can operate numerous qubits, while also being complex enough to be able to correct quantum calculation errors," says Anasua Chatterjee, a member of the research team. "Thus far, research in spin qubits has gotten to the point where circuits contain arrays of 2x2 or 3x3 qubits. The problem is that their qubits are only dealt with one at a time."
Think of it this way: you can't read the content of a letter until you actually manipulate the envelope they're in, opening it to scan what's inside. However, much in the same way that you change the state of the envelope in reaching the letter proper, qubits are changed when you try to read them. With quantum physics, manipulating a single qubit has up to now resulted in (essentially) catastrophic decoherence of the surrounding system. Basically, the results stop being accurate. This research now proves there is a way to operate and measure the entire qubit subsystem without that fall to chaos.
Chaterjee states, "The new and truly significant thing about our chip is that we can simultaneously operate and measure all qubits. This has never been demonstrated before with spin qubits — nor with many other types of qubits."
Of course, the breakthrough won't be able to stand on its own; research work is never done. As such, the researchers have identified the most pressing limitations on their approach. While the control mechanism employed by the scientists has been proven to maintain quantum coherence, its current design requires sustained, manual tuning of the 48 control electrodes that actually make the system work. The team is now looking to AI control systems that could automatically keep the system tuned with no human intervention. Perhaps this breakthrough will bring renewed focus on spin qubits as the fastest way to achieve a scalable, coherent, and efficient quantum computer. Time will tell.