In the race to create practical quantum computers, researchers have been focusing on optical systems. For instance, researchers from MIT recently made an important step towards quantum computing by developing a prototype chip that can trap ions in an electric field, and using built-in optics, direct laser light towards each of them.

But what if there was another way to build quantum computers without focusing on optical systems?

A team of researchers at Aalto University in Finland came up with a new answer: microwave signals.

“Today the basic architecture of future quantum computers is being developed very intensively around the world. By utilizing the multi-frequency microwave signals, an alternative approach can be pursued which realizes the logical gates by sequences of quantum measurements. Moreover, if we use the photons created in our resonator, the physical quantum bits or qubits become needless,” said Professor Pertti Hakonen from the Low Temperature Laboratory of Aalto University.


Artistic depiction of the generation of three correlated photons from quantum vacuum. (Credit: Antti Paraoanu)

For the study, published in journal Nature Communications, the team chilled a microwave resonator to nearly absolute zero temperature—freezing any thermal motion. This state, called a quantum vacuum, is akin to perfect darkness, but has fluctuations that can bring photons in and out of existence, albeit for just a very short time.

After turning these flickering photons into real ones, the researchers discovered that there is a “magic connection” between each of the photons.

“This all hints at the possibility of using the different frequencies for quantum computing. The photons at different frequencies will play a similar role to the registers in classical computers, and logical gate operations can be performed between them,” said Dr. Sorin Paraoanu, senior university lecturer and one of the co-authors of the work.

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