Magnons are tiny waves in the magnetization of solid magnetic materials that stay inside magnetic solids and can have extremely short wavelengths down to the nanometer scale. This property makes them promising for building very small circuits on chips. Magnons can also connect easily with other quantum particles such as phonons, which are vibrations in a crystal, making them useful for hybrid quantum systems that combine different technologies and for quantum metrology, which is ultra-precise measurement using quantum rules.
Until recently, magnons had a serious limitation. Their lifetime, the time they can carry quantum information reliably, was at most a few hundred nanoseconds. Researchers have now extended this lifetime a hundred times, reaching up to 18 microseconds. This change turns magnons from short-lived signals into stable carriers suitable for quantum information processing, similar to the superconducting qubits used in current quantum processors.
The advance came from two main changes. Scientists used short-wavelength magnons, which are less affected by tiny defects on the surface of the material. They also worked with ultra-pure spheres of yttrium iron garnet, a magnetic crystal known as YIG, and cooled them to 30 millikelvin in a special refrigerator. Millikelvin is a temperature only a fraction of a degree above absolute zero, where almost all heat-related disturbances stop.
Implications for quantum technology
This work shows that the lifetime of magnons is not set by any basic law of physics but depends on the purity of the materials. Tests with spheres of different purity levels confirmed that cleaner crystals allow magnons to last longer. Even the least pure sample in the study beat all earlier records. With lifetimes now at 18 microseconds, magnons can act as reliable quantum memories and low-loss links on a chip. They could connect many qubits, the basic units of quantum computers, along a shared pathway known as a quantum bus. Because magnons exist in solid materials and interact with various other quantum systems, they may serve as connectors in future hybrid quantum devices. This progress brings closer the possibility of quantum computers small enough to fit in the space of a one-cent coin.
This research is published in Science Advances.