ETH scientists create longest microwave quantum link

The Swiss Federal Institute of Technology in Zurich (ETH) explains in a press release that in order to build powerful quantum computers, several smaller quantum calculators must be connected to create a type of cluster or local network (LAN). The links between them must also be quantum links.

Physicists from the ETH have created the longest quantum link based on microwaves to date. It is five meters long and was created in the laboratory of Andreas Wallraff, professor at the Quantum Device Lab of the ETH. In the press release, Wallraff says that the quantum link is a milestone for the team since they can now “show that quantum-​LANs are possible in principle.”

Philipp Kurpiers, a former PhD student from Wallraff’s group explains: “The challenge was to connect two […] superconducting quantum chips in such a way as to be able to exchange superposition states between them with minimal decoherence.” This occurs by microwave photons being emitted by one superconducting oscillator and received by another. It is important to cool the waveguide needed for this sufficiently, which the scientists were able to do in their model.

The ETH scientists were not only able to prove that the quantum link can be cooled to the extent required, but also that quantum information can actually be transmitted reliably between two quantum chips using it.

The statement states that in addition to uses in future quantum computers, the ETH researchers’ link is also suited for experiments in the area of basic quantum physics research. The physicists had planned to present their results at the annual meeting of the American Physical Society in Denver, but this has been called off due to coronavirus. Instead, the scientists reported their results recently at a virtual substitute conference.