A team of scientists at the U.S. Department of Energy's Argonne National Laboratory, have achieved efficient quantum coupling between two distant magnetic devices, which can host a certain type of magnetic excitations called magnons. These excitations happen when an electric current generates a magnetic field. Coupling allows magnons to exchange energy and information. This kind of coupling may be useful for creating new quantum information technology devices.

This instant communication does not require sending a message between magnons limited by the speed of light. It is analogous to what physicists call quantum entanglement. Following on from a 2019 study, the researchers sought to create a system that would allow magnetic excitations to talk to one another at a distance in a superconducting circuit. This would allow the magnons to potentially form the basis of a type of quantum computer. For the basic underpinnings of a viable quantum computer, researchers need the particles to be coupled and stay coupled for a long time.

To achieve a strong coupling effect, researchers built a superconducting circuit and used two small yttrium iron garnet (YIG) magnetic spheres embedded on the circuit. This material, which supports magnonic excitations, ensures efficient and low-loss coupling for the magnetic spheres.

The two spheres are both magnetically coupled to a shared superconducting resonator in the circuit, which acts like a telephone line to create strong coupling between the two spheres even when they are almost a centimeter away from each other — 30 times the distance of their diameters.

One additional improvement over the 2019 study involved the longer coherence of the magnons in the magnetic resonator. According to the team, because the magnetic spins are highly concentrated in the device, the study could point to miniaturizable quantum devices.

The magnonic devices were fabricated at Argonne's Center for Nanoscale Materials, a DOE Office of Science user facility. A paper based on the study, “Coherent coupling of two remote magnonic resonators mediated by superconducting circuits,” was published in the Physical Review Letters.

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