Reviewed by Lexie CornerApr 29 2024
According to a study published in the journal Physical Review Research, researchers Kazuaki Takasan and Kyogo Kawaguchi of the University of Tokyo, along with Kyosuke Adachi of RIKEN, Japan’s largest comprehensive research institution, have demonstrated that increasing particle motility can induce ferromagnetism (an ordered state of atoms) and that repulsive forces between atoms are sufficient to maintain it.
Schematic picture of activity-induced ferromagnetism in quantum active matter. Here, moving atoms with spins exhibit the ferromagnetic order (that is, aligning in one direction) like a flock of birds depicted above. Image Credit: The University of Tokyo
The finding not only extends the idea of active matter to quantum systems but also adds to the creation of new technologies based on particle magnetic characteristics, such as magnetic memory and quantum computing.
Flocking birds, swarming bacteria, and cellular flows are all instances of active matter, which is the condition in which individual agents, such as birds, bacteria, or cells, arrange themselves. During a “phase transition,” the agents go from disordered to ordered. As a result, they move in an organized way without using an external controller.
Previous studies have shown that the concept of active matter can apply to a wide range of scales, from nanometers (biomolecules) to meters (animals). However, it has not been known whether the physics of active matter can be applied usefully in the quantum regime. We wanted to fill in that gap.
Kazuaki Takasan, Assistant Professor, Department of Physics, University of Tokyo
To close the gap, the scientists had to present a potential mechanism for inducing a quantum system and maintaining it in an ordered state. It was a joint effort between biophysics and physics. The researchers were inspired by the phenomenon of flocking birds because, due to the activity of each agent, the ordered state is more easily created than in other forms of active matter.
They developed a theoretical model in which atoms mimicked the behavior of birds. In this concept, increasing atom motility caused the repulsive interactions between atoms to reorganize themselves into an ordered state known as ferromagnetism. Spins, or angular momentum of subatomic particles and nuclei, align in one direction in the ferromagnetic state, exactly as flocking birds do while flying.
“It was surprising at first to find that the ordering can appear without elaborate interactions between the agents in the quantum model. It was different from what was expected based on biophysical models,” Takasan added.
The researcher used a multifaceted method to guarantee their discovery was not a fluke. Fortunately, the findings of computer simulations (mean-field theory, a statistical theory of particles, and mathematical proofs based on linear algebra) were consistent. This increased the credibility of their discovery, the first step in a new line of investigation.
Takasan concluded, “The extension of active matter to the quantum world has only recently begun, and many aspects are still open. We would like to further develop the theory of quantum active matter and reveal its universal properties.”
Journal Reference:
Takasan, K., et. al. (2024) Activity-induced ferromagnetism in one-dimensional quantum many-body systems. Physical Review Research. doi:10.1103/PhysRevResearch.6.023096