Researchers hit crucial milestone for scalable quantum technology

25 Mar 2021

Schematic of the four-qubit quantum processor. Image: QuTech

Researchers used semiconductor technology to build a two-dimensional array of qubits to function as a quantum processor.

A computer’s central processing unit is built using semiconductor technology, which can put billions of transistors on a single chip. Now, researchers have found a way to use this process to advance the scalability of quantum technology.

Researchers at QuTech, a collaboration between TU Delft and TNO in the Netherlands, have demonstrated how semiconductor technology can be used to build a two-dimensional array of qubits to function as a quantum processor.

The team said that this work, which is published in Nature, marks an important step towards a scalable approach to quantum computation.

While current quantum devices hold tens of qubits, a future universal quantum computer capable of running any quantum algorithm will likely consist of millions or even billions of qubits.

Electrons trapped in quantum dots, which are tiny semiconductor structures, have been studied for years as a platform for quantum information. Scaling beyond two-qubit logic has remained elusive, however this new research demonstrates a four-qubit quantum processor.

The team worked with holes (missing electrons) in germanium, a highly versatile material used in quantum technologies. Using this approach, the same electrodes needed to define the qubits could also be used to control and entangle them.

“By putting four such qubits in a two-by-two grid, demonstrating universal control over all qubits, and operating a quantum circuit that entangles all qubits, we have made an important step forward in realising a scalable approach for quantum computation,” said Menno Veldhorst, who leads the team of researchers at QuTech.

“Four qubits by no means makes a universal quantum computer, of course. But by putting the qubits in a two-by-two grid we now know how to control and couple qubits along different directions.

“Now that we know how to manufacture germanium and operate an array of qubits, the germanium quantum information route can truly begin.”

The research was supported by NWO, the Dutch organisation for scientific research.

In December 2020, another quantum computing breakthrough occurred when a team of researchers demonstrated sustained long-distance teleportation of qubits of photons.

Jenny Darmody is the editor of Silicon Republic