Paul van Gerven
25 March

Qutech researchers have successfully obtained two-dimensional control and coupling over a two-by-two array of germanium quantum dot qubits. This is a crucial step toward scalable quantum processors, they claim.

A future universal quantum computer will likely need millions, or even billions, of qubits to complete sophisticated tasks. To reach these numbers, a scalable technology is required. Since no technology is more scalable than semiconductor technology, it’s a prime candidate. Instead of transistors, however, quantum dots are used to define qubits.

Schematic of the 4-qubit quantum processor made using semiconductor manufacturing technology. Credit: Nico Hendrickx/Qutech

Electrons trapped in quantum dots have been studied for more than two decades as a platform for quantum information. Despite all promises, scaling beyond 2-qubit logic has remained elusive. To break this barrier, the Qutech groups of Menno Veldhorst and Giordano Scappucci decided to take an entirely different approach and started to work with holes (ie missing electrons) in germanium.

After successfully creating the first germanium quantum dot qubit in 2019, the researchers have now put four qubits in a two-by-two grid, which they can control and couple along different directions. This interconnection along two dimensions is required for integrating large numbers of qubits into a quantum processor.