The era of quantum computers is coming soon. The sheer power of these machines is in direct proportion to the number of qubits. However, a probable break in the development is the difficulty in controlling a large number of qubits simultaneously.

This is a big challenge. Nowadays experimental quantum computers consist of a small number of qubits. The biggest problem for researchers and developers is how to achieve scalability to millions of qubits in order to execute complex algorithms. The main problem is the lack of techniques to control the big number of qubits and at the same time to perform error-checking on each qubit.

Solutions have been tried in many research centers, to no big success. Now, scientists at TU Delft in collaboration with scientists at the Netherlands Organization for Applied Scientific Research (TNO in Dutch) discovered a solution to this problem.

Richard Versluis at TNO and Leo DiCarlo and Stefano Poleto at TU Delft with support from colleagues at Intel developed a control strategy for fault-tolerant quantum computing based on a building block of eight qubits using a fixed set of control hardware.

Control arrangement. Source: TNOThe team claims that this basic block can be reproduced on a very large grid of qubits, from 8 to 8 million or more, without any increase in the complexity of the control algorithm or hardware. To control a basic block of eight qubits, the researchers used a control hardware the size of a small bookcase. This will allow programmers to control and to execute computing algorithms on individual qubits on machines with any number of qubits.

The next step for researchers is to expand the testing platform to 17-qubit processors to control each qubit and to perform error-checking on each qubit. This constitutes a world first.

The results of the research are published in the journal Physical Review Applied. An abstract is found here: https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.8.034021