Tiny magnets could hold the secret to new quantum computers

Date:
March 21, 2022
Source:
DOE/Argonne National Laboratory
Summary:
Scientists have discovered a type of magnetic behavior that could
help enable magnetically based quantum devices.



FULL STORY ========================================================================== Magnetic interactions could point to miniaturizable quantum devices.


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

In new research from the U.S. Department of Energy's (DOE) Argonne
National Laboratory, scientists 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.

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

In order to achieve a strong coupling effect, researchers have 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.

"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 indirect interaction between the two spheres and
the shared superconducting resonator." One additional improvement
over the 2019 study involved the longer coherence of the magnons in
the magnetic resonator. ​"If you speak in a cave, you may hear an
echo," said Novosad. ​"The longer that echo lasts, the longer the coherence." "Before, we definitely saw a relationship between magnons
and a superconducting resonator, but in this study their coherence times
are much longer because of the use of the spheres, which is why we can
see evidence of separated magnons talking to each other," Li added.

According to Li, because the magnetic spins are highly concentrated
in the device, the study could point to miniaturizable quantum
devices. ​"It's possible that tiny magnets could hold the secret
to new quantum computers," he said.


========================================================================== Story Source: Materials provided by
DOE/Argonne_National_Laboratory. Original written by Jared Sagoff. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Yi Li, Volodymyr G. Yefremenko, Marharyta Lisovenko, Cody
Trevillian,
Tomas Polakovic, Thomas W. Cecil, Peter S. Barry, John Pearson,
Ralu Divan, Vasyl Tyberkevych, Clarence L. Chang, Ulrich Welp,
Wai-Kwong Kwok, Valentine Novosad. Coherent Coupling of Two Remote
Magnonic Resonators Mediated by Superconducting Circuits. Physical
Review Letters, 2022; 128 (4) DOI: 10.1103/PhysRevLett.128.047701 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220321115840.htm

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