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For years, magnons looked like a dead end for quantum technology, interesting in theory but gone before anyone could use them. A team led by Andrii Chumak at the University of Vienna has changed that. Working with collaborators at the University of Colorado Colorado Springs and institutions in Germany, the United States, and Ukraine, the physicists stretched magnon lifetimes from a few hundred nanoseconds to as long as 18 microseconds, an increase of nearly a hundredfold. The results, published in the journal Science Advances, suggest a practical path toward quantum computers small enough to fit on a coin.
A magnon is a wave of magnetization that ripples through a solid magnetic material, similar to how a stone thrown into a pond sends ripples across the surface. Unlike photons, which can travel through open space or fiber optic cable, magnons only exist inside magnetic solids. That might sound limiting, but it is actually the appeal. Because their wavelengths can shrink down to a few nanometers, circuits built from magnons could fit on chips no bigger than the ones already inside a smartphone. Magnons also interact naturally with other quantum particles such as phonons and photons, which makes them attractive as connectors between different kinds of quantum hardware rather than just another way to store a bit of information.
The catch has always been survival time. A magnon that lasts only a few hundred nanoseconds decays before it can reliably carry or store quantum information, ruling it out for real computation. Reaching 18 microseconds changes the calculus entirely. At that duration, magnons start to approach the timescales used by superconducting qubits, the technology behind most of today’s leading quantum processors, according to the University of Vienna team. A magnon that survives that long stops being a fleeting signal and starts behaving like usable quantum memory.
The team got there by combining two techniques. Instead of exciting ordinary uniform magnons, they generated short wavelength magnons, which are naturally less bothered by tiny defects on the surface of the crystal, the very defects that had capped lifetimes in earlier experiments. Then they cooled ultra pure spheres of yttrium iron garnet, a synthetic magnetic material widely used in this kind of research, down to just 30 millikelvin inside a specialized cryostat, a fraction of a degree above absolute zero. At that temperature, the thermal noise that normally scrambles magnons is essentially switched off.
What happened next is arguably the more important finding. The researchers tested three yttrium iron garnet spheres of varying purity and found a direct relationship: the cleaner the crystal, the longer its magnons survived, and even the least pure sample beat every prior record. That tells the team the remaining ceiling on magnon lifetime is not a law of physics standing in the way, but a materials engineering problem that better manufacturing can keep chipping away at. Rostyslav Serha, the doctoral researcher whose thesis work forms the basis of the study, led the hands on experiments under Chumak’s supervision.
The practical payoff, if the approach scales, is significant. Long lived magnons could act as a kind of quantum bus, a shared pathway able to link hundreds of qubits together on a single chip, something quantum computing has lacked as it tries to grow beyond small demonstration systems. Because magnons couple so readily to other quantum particles, they could also serve as translators between otherwise incompatible quantum technologies, letting different hardware approaches talk to each other instead of existing in isolation.
None of this puts a magnon based quantum computer on a lab bench next year. Cooling a crystal to 30 millikelvin and exciting short wavelength magnons with precision is still delicate, specialized work. But the message from Vienna is that the biggest obstacle just moved from the realm of fundamental physics into the realm of materials science, where progress tends to be steadier and more predictable. If purer crystals keep pushing lifetimes higher, magnons may go from a scientific curiosity to a genuine building block sitting inside future quantum machines.
Source: University of Vienna and the study in Science Advances (DOI 10.1126/sciadv.aee2344). Credit: University of Vienna.