There’s a new quantum computing record: control of a 6-qubit processor in silicon

Another record was broken on the way to fully functional and powerful quantum computers: full control over a 6-qubit quantum processor in silicon.

Researchers call it “an important stepping stone” for the technology.

Qubits (or quantum bits) are the quantum equivalent of classical computational bits, only they can potentially handle much more information. Thanks to quantum physics, they can be in two states at once, rather than just a single 1 or 0.

The difficulty is getting many qubits to behave the way we need them to, which is why this jump to six is ​​important. The ability to operate them in silicon – the same material used in today’s electronic devices – makes the technology potentially more viable.

“The quantum computing challenge today consists of two parts,” says quantum computing researcher Stephan Philips of Delft University of Technology in the Netherlands. “To develop qubits that are of sufficiently good quality and to develop an architecture that makes it possible to build large systems of qubits.”

“Our work fits into both categories. And since the overall goal of building a quantum computer is an enormous effort, I think we can rightly say that we have made a contribution in the right direction.”

The qubits consist of individual electrons fixed in a row, 90 nanometers apart (a human hair is about 75,000 nanometers in diameter). This array of “quantum dots” is placed in silicon using a structure similar to the transistors used in standard processors.

By making careful improvements to the way the electrons were prepared, managed and monitored, the team was able to successfully control their spin – the quantum mechanical property that enables the qubit state.

Researchers were also able to create logic gates on demand and entangle two- or three-electron systems with low error rates.

Researchers used microwave radiation, magnetic fields, and electric potentials to control and read electron spins, operate them as qubits, and make them interact with each other as needed.

“In this research we push the limits of the number of qubits in silicon and achieve high initialization fidelity, high read fidelity, high single-qubit gate fidelity and high two-qubit state fidelity,” says electrical engineer Lieven Vandersypen from Delft University of Technology.

“What’s really striking is that we’re demonstrating all of these properties together in a single experiment on a record number of qubits.”

Up to this point, only 3-qubit processors have been successfully built in silicon and controlled to the required level of quality – so we’re talking about a major advance in terms of what’s possible with this type of qubit.

There are several ways to build qubits — including on superconductors, where many more qubits have been run together — and scientists are still figuring out which method might be the best way forward.

The benefit of silicon is that the manufacturing and supply chains are already in place, meaning the transition from a science lab to an actual machine should be easier. Work continues to push the qubit record even higher.

“With careful design, it is possible to increase the number of silicon spin qubits while maintaining the same precision as single qubits,” says electrical engineer Mateusz Madzik from Delft University of Technology.

“The key building block developed in this research could be used to add even more qubits in the next iterations of the study.”

The research was published in Nature.