A device that uses supersized rubidium atoms could make it possible to transmit outputs from quantum computers through standard optical fibres. That in turn could make it easier to build networks of quantum computers.
Supersized atoms can convert the output of quantum computers into light signals that can travel through optical fibres. This could be crucial for connecting quantum computers into a network.
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| The device could enable quantum computers to transmit signals through optical fibres Shutterstock/Valentyn Volkov |
Multiple quantum computers networked together may be able to handle more complex computations than just one computer. However, while conventional computer networks use optical fibres for fast and accurate connections, many quantum computers output their results as signals that can’t travel through fibres. Consequently, quantum computers have been linked to each other only in a few specific instances and there is no universal recipe for how to build the best connection between any two quantum computers.
Aziza Suleymanzade at Harvard University and her colleagues wanted to build a device that could remedy the incompatibility between quantum computers and optical fibres. They focused on superconducting quantum computers that output photons, or particles associated with electromagnetic radiation, that had wavelengths of a few millimetres. Millimetre-wave photons are too big to travel through fibres, but photons with the smaller wavelengths of light can. So, the researchers’ device had to convert between the two.
The researchers started with a 2-centimetre-long rectangular piece of niobium metal, a material that conducts electricity perfectly when sufficiently cooled. They bored three narrow tunnels into the metal that intersected in the middle. The researchers turned on the niobium’s superconductivity by placing it in a powerful fridge that maintained -268°C (-450°F). Then, they ran a beam of millimetre-waves through one tunnel – the equivalent of having a quantum computer output signals within the metal.
They filled the second tunnel with thousands of very cold, giant rubidium atoms that were capable of absorbing these millimetre-wave photons and responding by emitting light photons – the signal the researchers wanted to end up with. The rubidium atoms, which were supersized because some of their electrons were unusually far from the nucleus, could achieve this conversion only when these faraway electrons had specific levels of energy. The researchers could ensure the electrons had the right energy by hitting the atoms with a blue and an ultraviolet laser. They shined this laser down the third tunnel in the metal.
Johannes Fink at the Institute of Science and Technology Austria says that the new device could also be used to connect superconducting quantum computers to other types of quantum computers, like those built from charged atoms. This would create new, hybrid computers that haven’t been tested on many problems before, says Fink.
Similar devices have been built before, but they were either hundreds of times less efficient or produced more meaningless photons alongside those that were a translation of millimetre-wave signals. Suleymanzade says that the team expects the device to reach nearly perfect efficiency in the future when they will put it in an even colder fridge, at -272°C.
Journal reference
Nature: DOI: 10.1038/s41586-023-05740-2