Tiny magnets could hold the secret to new quantum computers

Magnetic interactions could point to miniaturizable quantum devices.

From MRI machines to computer hard drive storage, magnetism has played a role in pivotal discoveries that are reshaping our society. In the new field of quantum computing, magnetic interactions could play a role in relaying quantum information.

In new research from the US Department of Energy’s (DOE) Argonne National Laboratory, scientists have obtained an efficient quantum coupling between two distant magnetic devices, which may harbor a certain type of magnetic excitations called magnons. These excitations occur when an electric current generates a magnetic field. The coupling allows the magnons to exchange energy and information. This type of coupling can be useful for creating new quantum information technology devices.

“Remote coupling of magnons is the first step, or almost a prerequisite, to doing quantum work with magnetic systems,” said Argonne senior scientist Valentine Novosad, author of the study. “We show the ability of these magnons to instantly communicate with each other remotely.”

This instantaneous communication does not require sending a message between magnons limited by the speed of light. It’s analogous to what physicists call quantum entanglement.

Following a 2019 study, researchers sought to create a system that would allow magnetic excitations to talk to each other remotely in a superconducting circuit. This would allow magnons to potentially form the basis of a type of quantum computer. For the foundations of a viable quantum computer, researchers need particles to be coupled and to remain coupled for a long time.

In order to achieve a strong coupling effect, the researchers constructed a superconducting circuit and used two small magnetic yttrium iron garnet (YIG) spheres embedded in the circuit. This material, which supports magnonic excitations, ensures efficient and low-loss coupling of 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 a strong coupling between the two spheres even when they are nearly a centimeter apart – 30 times the distance of their diameters.

“This is a significant achievement,” said Argonne materials scientist Yi Li, lead author of the study. “Similar effects can also be observed between magnons and superconducting resonators, but this time we did it between two magnon resonators without direct interaction. The coupling comes from the indirect interaction between the two spheres and the shared superconducting resonator. “

An additional improvement over the 2019 study was the longer coherence of the magnons in the magnetic resonator. “If you speak in a cave, you can hear an echo,” Novosad said. “The longer the echo lasts, the longer the coherence.”

“Before, we have certainly seen a relationship between magnons and a superconducting resonator, but in this study their coherence times are much longer due to the use of spheres, which is why we can see evidence of magnons separated talking to each other,” Li added.

According to Li, since the magnetic spins are highly concentrated in the device, the study could indicate miniaturizable quantum devices. “It’s possible that tiny magnets hold the secret to new quantum computers,” he said.

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Material provided by DOE/Argonne National Laboratory. Original written by Jared Sagoff. Note: Content may be edited for style and length.