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Successful experiment with microwaves could result in better quantum computers

Photo of two researchers holding a brass component with microwave circuits.
Physics researchers Peter Samuelsson, on the left, and Ville Maisi show the small brass component that contains connectors, microwave circuits and nanowires. Photo: Simon Wosny

In a pioneering nano experiment, a research team in Lund has successfully constructed a new and very efficient microwave photon detector. The discovery could accelerate the development of future quantum computers.

Microwaves are a collective term for electromagnetic radiation in the higher radio frequency bands; they can be used for everything from warming up fish dishes to searching for extraterrestrial life in the universe. Above all, microwaves are used to transfer signals in telecommunication. However, in recent years, researchers have increasingly focused on the potential of microwaves in quantum technology – a field that uses quantum mechanical properties to solve measurement and computational problems beyond the scope of traditional technologies. Now, a research team at Lund University in Sweden has made a discovery that could accelerate quantum development. In an article published in the research journal Nature Communications, the researchers describe how their experiment enabled them to develop a detector for microwave photons.

“For communication between the parts of a quantum computer to be possible, you have to be able to detect individual microwave photons very efficiently. Our experiment shows a completely new way of achieving this”, says Peter Samuelsson, a physics researcher at Lund University and a principal investigator at NanoLund.

Close-up of a detector.
Close-up of the new detector. The nanowire used is so small that it is not even visible in a light microscope. Photo: Waqar Khan

In the study, researchers created a detector using semiconducting nanowires. A major advantage of these nanowires is their ability to connect to existing technology. Their properties also form the basis for the major breakthrough.

“It is thanks to the nanowires that we succeeded in detecting photons continuously, by converting them into a measurable flow of electrons. This means that the detector does not need to know when the photon arrives, which is often required in the microwave detectors that are currently available”, says Ville Maisi, a physics researcher at Lund University and a principal investigator at NanoLund.

More progress within reach

Detectors of individual photons of visible light have existed for a long time and are used in many areas of technology. Now the Lund researchers can establish that the basic principles also work for microwave photons, despite the latter having only one ten-thousandth of the energy. In the experiment, the researchers were able to show that six percent of all photons were converted into electrons. That is around a thousand times better than the results measured in previous experiments. The work now continues in the nanolab.

“Our theoretical analyses show that we can achieve close to one hundred percent efficiency by refining the experiment. We hope that our results will be the starting point for the development of ultrasensitive detectors for use in a number of technological fields”, says Peter Samuelsson.

The study has been published in the research journal Nature Communications:
“Efficient and continuous microwave photoconversion in hybrid cavity-semiconductor nanowire double quantum dot diodes”