Physicists at ETH Zurich have demonstrated a five-metre-long microwave quantum link, the longest of its kind to date. It can be used both for future quantum computer networks and for experiments in basic quantum physics research.
Collaboration is everything – also in the quantum world. To build powerful quantum computers in the future, it will be necessary to connect several smaller computers to form a kind of cluster or local network (LAN). Since those computers work with quantum mechanical superposition states, which contain the logical values “0” and “1” at the same time, the links between them should also be “quantum links”.
The longest such link to date based on microwaves, at five metres long, was recently built in the laboratory of Andreas Wallraff, professor at the Quantum Device Lab at ETH Zurich. The researchers were scheduled to present their results on it at the annual meeting of the American Physical Society in Denver. Because of the current epidemic situation this conference was cancelled at short notice. Instead, the scientists now report their results at a virtual substitute conference.
“That’s really a milestone for us”, Wallraff explains, “since now we can show that quantum-LANs are possible in principle. In the next 10 to 20 years, quantum computers will probably increasingly rely on them.” Currently there are computers with a few dozen quantum bits or qubits, but several hundreds of thousands of them are almost impossible to accommodate in existing devices. One reason for this is that qubits based on superconducting electrical oscillators, such as those used in the quantum chips in Wallraff’s lab (and also by IBM and Google), need to be cooled down to temperatures close to the absolute zero of -273,15 degrees Celsius. This supresses thermal perturbations that would cause the quantum states to lose their superposition property – this is known as decoherence – and hence errors in the quantum calculations to occur.
Source: “Longest microwave quantum link”, Oliver Morsch, Zurich ETH News