March 13, 2025
The University of Tokyo
Keio University
Japan Science and Technology Agency (JST)
Key Points of the Announcement
◆ Proposed a new method for measuring the noise of a magnet's strength (magnetization) using light.
◆ Enables observation of the quantization of spin in magnets, which has been difficult to observe until now.
◆ Contributes to the technological development of new quantum information devices using the spin of magnets.
A research group—comprising Tetsuya Sato, a graduate student (in the Doctoral Program of the Graduate School of Science), and Associate Professor Takeo Kato from the Institute for Solid State Physics at The University of Tokyo; Professor Shinichi Watanabe from Keio University; and Associate Professor Mamoru Matsuo from the Kavli Institute for Theoretical Sciences, University of Chinese Academy of Sciences—has theoretically proposed a new method for measuring magnetization noise using the optical pump-probe method. By formulating the noise, they also revealed that the noise intensity contains information about the "quantization of magnetization." This shows that the quantization of magnetization, which has been difficult to observe until now, can be directly observed from noise.
Noise is generally considered a nuisance in measurements, but it can sometimes contain important information. A prime example of this is the "quantization of magnetization." The magnitude of magnetization is thought to take discrete values, and a method involving the creation of a magnet-metal junction to measure the resulting current noise in the metal has been discussed. However, this has not been realized due to the technical difficulties of observing current noise.
Meanwhile, recent advances in optical measurement technology have been remarkable, and techniques for efficiently and rapidly measuring magnetization are being developed. This research focuses on such optical measurement technologies and presents a new proposal for measuring magnetization noise using light. This is expected to contribute to the development of quantum information devices that use quantized magnetization in magnets.
This research was published in the online edition of the American scientific journal "Physical Review Letters" on March 12 (local time).
For the full press release, please see below.