Quantum state of single electrons controlled by ‘surfing’ on sound waves


14-10-2019
  3D render of the semiconductor nanostructure  Credit: Hermann Edlbauer

Researchers have successfully used sound waves to control quantum information in a single electron, a significant step towards efficient, robust quantum computers made from semiconductors.

The international team, including researchers from the University of Cambridge, sent high-frequency sound waves across a modified semiconductor device to direct the behaviour of a single electron, with efficiencies in excess of 99%. The results are reported in the journal Nature Communications.

A quantum computer would be able to solve previously unsolvable computational problems by taking advantage of the strange behaviour of particles at the subatomic scale, and quantum phenomena such as entanglement and superposition. However, precisely controlling the behaviour of quantum particles is a mammoth task.

“What would make a quantum computer so powerful is its ability to scale exponentially,” said co-author Hugo Lepage, a PhD candidate in Cambridge’s Cavendish Laboratory, who performed the theoretical work for the current study. “In a classical computer, to double the amount of information you have to double the number of bits. But in a quantum computer, you’d only need to add one more quantum bit, or qubit, to double the information.”

Last month, researchers from Google claimed to have reached ‘quantum supremacy’, the point at which a quantum computer can perform calculations beyond the capacity of the most powerful supercomputers. However, the quantum computers which Google, IBM and others are developing are based on superconducting loops, which are complex circuits and, like all quantum systems, are highly fragile.

“The smallest fluctuation or deviation will corrupt the quantum information contained in the phases and currents of the loops,” said Lepage. “This is still very new technology and expansion beyond the intermediate scale may require us to go down to the single particle level.”

Instead of superconducting loops, the quantum information in the quantum computer Lepage and his colleagues are devising use the ‘spin’ of an electron – its inherent angular momentum, which can be up or down – to store quantum information.

“Harnessing spin to power a functioning quantum computer is a more scalable approach than using superconductivity, and we believe that using spin could lead to a quantum computer which is far more robust, since spin interactions are set by the laws of nature,” said Lepage.

Using spin allows the quantum information to be more easily integrated with existing systems. The device developed in the current work is based on widely-used semiconductors with some minor modifications.

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Image:  3D render of the semiconductor nanostructure

Credit: Hermann Edlbauer

Reproduced courtesy of the University of Cambridge

 

The University of Cambridge is acknowledged as one of the world's leading higher education and research institutions. The University was instrumental in the formation of the Cambridge Network and its Vice- Chancellor, Professor Stephen Toope, is also the President of the Cambridge Network.

University of Cambridge (cam.ac.uk)