Another record has been broken on the way to fully operational and capable quantum computers: complete control of a 6-qubit silicon quantum processor.
The researchers call it “a major stepping stone” for the technology.
Qubits (or quantum bits) are the quantum equivalents of classical computer bits, alone they can potentially process much more information. Thanks to quantum physics, they can be in two states at once, rather than a single 1 or 0.
The difficulty is getting a lot of qubits to behave the way we need them to, which is why this jump to six is important. Being able to run them in silicon – the same material used in today’s electronic devices – makes the technology potentially more viable.
“The challenge of quantum computing today consists of two parts,” explains Stephan Philips, a quantum computing researcher at Delft University of Technology in the Netherlands. “Develop qubits of sufficient quality and develop an architecture to build large qubit systems.”
“Our work falls into both categories. And since the overall goal of building a quantum computer is a massive effort, I think it’s fair to say we’ve made a contribution in the right direction.”
Qubits are made up of individual electrons fixed in a row, 90 nanometers apart (a human hair is about 75,000 nanometers in diameter). This line 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 electrons were prepared, managed and monitored, the team was able to successfully control their spin – the quantum mechanical property that enables the qubit state.
The researchers were also able to create logic gates and entanglement systems of two or three electrons, on demand, with low error rates.
The researchers used microwave radiation, magnetic fields and electric potentials to control and read the spin of electrons, harnessing them like qubits and causing them to interact with each other as needed.
“In this research, we push the limits of the number of qubits in silicon and achieve high initialization fidelities, high read fidelities, high single-qubit gate fidelities, and high two-qubit state fidelities. “says electrical engineer Lieven Vandersypen, also from Delft University of Technology.
“What really stands out is that we’re demonstrating all of these features together in a single experiment on a record number of qubits.”
So far only 3-qubit processors have been successfully built in silicon and tested to the necessary level of quality – so we are talking about a big step forward in terms of what is possible in this type of qubit .
There are different ways to build qubits — including on superconductors, where many other qubits have been mined together — and scientists are still figuring out which method might be the best way forward.
The advantage of silicon is that the manufacturing and supply chains are already in place, which means the transition from a science lab to an actual machine should be easier. The work continues to push the qubit record even higher.
“With careful engineering, it is possible to increase the number of silicon spin qubits while maintaining the same precision as for single qubits,” says electrical engineer Mateusz Madzik of Delft University of Technology.
“The key building block developed in this research could be used to add even more qubits in future iterations of the study.”
The research has been published in Nature.