The spin of an electron is nature’s perfect quantum bit, which can expand the range of information storage beyond “one” or “zero.” Exploiting the electron’s spin degrees of freedom (possible spin states) is one of the main goals of quantum information science.

Recent advances by Lawrence Berkeley Laboratory researchers Joseph Orenstein, Yue Sun, Jie Yao, and Fanhao Meng have demonstrated the potential of magnon wave packets (collective excitations of electron spin) to transport quantum information over significant distances in a class of materials known as antiferromagnets.

Their work overturns the traditional understanding of how such excitations propagate in antiferromagnets. The future era of quantum technologies (computers, sensors and other devices) depends on the precise transmission of quantum information over long distances.

Thanks to his discovery published in the journal Natural PhysicsOrenstein and his colleagues hope to get one step closer to these goals. Their research is part of Berkeley Lab’s broader effort to advance quantum knowledge across the quantum research ecosystem by working from theory to application, producing and testing quantum-based devices, and developing software and algorithms.

Electron spins are responsible for magnetism in materials and can be thought of as small bar magnets. When adjacent spins are oriented in different directions, the result is an antiferromagnetic arrangement and the arrangement produces no net magnetization.

To understand how magnon wave packets propagate through an antiferromagnetic material, Orenstein’s group created snapshots of their propagation using pairs of laser pulses that disrupt the antiferromagnetic pattern at one location and probe another. These images showed that the magnon wave packets were spreading in all directions, like the ripples created by a pebble falling into a pond.

The Berkeley Lab team also showed that magnon wave packets in the antiferromagnet CrSBr (chromium bromide sulfide) propagate faster and over greater distances than current models predict. The models assume that each electron spin binds only to its neighbors. An analogy is a system of spheres connected to their nearest neighbors by springs; Moving a sphere from its desired position creates a shear wave that propagates over time.

Surprisingly, such interactions predict diffusion rates that are much slower than what the team actually observed.

“But remember that each spinning electron is like a small bar magnet. If we imagine that the spheres are replaced by small bar magnets representing spinning electrons, the picture changes completely,” Orenstein said. “Now, instead of a local interaction, each bar magnet is connected to each other in the entire system through the same long-range interaction that pulls the refrigerator magnet towards the refrigerator door. “