Longer-lived magnons point to smaller quantum computing hardware

A University of Vienna-led physics team has kept magnons alive far longer than earlier experiments, removing a key barrier to using the magnetic waves in quantum devices. The finding matters because magnons could help carry or store quantum information in hardware small enough for highly compact chips, according to the university.

The researchers increased magnon lifetimes from a few hundred nanoseconds to as much as 18 microseconds, the University of Vienna said. The work, published in Science Advances, was led by Andrii Chumak and involved collaborators from the University of Colorado Colorado Springs and institutions in Germany, the United States and Ukraine.

Magnetic waves with quantum potential

Magnons are waves of magnetization that travel through magnetic solids, according to the University of Vienna. The university compares them to ripples moving across water, while noting that magnons stay inside magnetic material rather than traveling through open space or optical fiber as photons can.

Their short wavelengths can reach only a few nanometers, the university said. That property has made them candidates for dense circuits on chips comparable in size to those used in smartphones, and for systems that combine different quantum components.

According to the University of Vienna, magnons also couple naturally with other quasiparticles, including phonons and photons. That makes them useful candidates for hybrid quantum systems and quantum measurement technologies, the university said.

Cooling and cleaner crystals

The main technical problem has been lifetime, according to the research team. Earlier magnons vanished after only a few hundred nanoseconds, too quickly for dependable quantum information storage or transfer, the university said.

The team used short-wavelength magnons instead of conventional uniform magnons, according to the University of Vienna. The university said those shorter waves are less affected by small surface defects in the crystal, a problem that had reduced lifetimes in earlier work.

The researchers also used very pure spheres of yttrium iron garnet, or YIG, and cooled them to 30 millikelvin in a mixed-phase cryostat, according to the university. At that temperature, close to absolute zero, thermal effects that normally destroy magnons are largely suppressed, the university said.

Material quality sets the ceiling

The team tested three YIG spheres with different purity levels, according to the University of Vienna. The university said the cleaner samples produced longer-lived magnons, while even the least pure sample exceeded previous experimental results.

That pattern led the researchers to conclude that magnon lifetime is now limited mainly by material quality rather than by a fundamental physical boundary, according to the university. If manufacturers can produce purer magnetic materials, the university said, magnon lifetimes may be extended further.

With lifetimes up to 18 microseconds, magnons are approaching timescales relevant to practical quantum technologies and are comparable with superconducting qubits used in leading quantum processors, according to the University of Vienna. The researchers say the waves could serve as quantum memory elements or low-loss routes for moving quantum information across a chip.

The university said magnons may eventually connect many qubits through a shared channel, sometimes called a quantum bus. Because they can interact with several types of quantum systems, the research team also sees them as possible links between technologies that otherwise do not easily exchange information.

The experiments were carried out by Rostyslav O. Serha during doctoral work, according to the University of Vienna. Kaitlin H. McAllister, Fabian Majcen, Sebastian Knauer, Timmy Reimann, Carsten Dubs, Gennadii A. Melkov, Alexander A. Serga, Vasyl S. Tyberkevych, Chumak and Dmytro A. Bozhko are listed as co-authors in Science Advances.

This story draws on original reporting from ScienceDaily.