Frontier Research Institute for Interdisciplinary Sciences
Tohoku University

A precision measurement of a magnetic field and its change has an important role in not only the fundamental physics but also the medical science. In the fundamental physics, since the change of the magnetic field induces a change in a spin precession frequency of an elementary particle, which constitutes a matter, the observable related to the spin can be understood through its precision measurement. For example, an experimental search for a permanent electric dipole moment of the particle, which is a suitable observable for the discovery of the physics beyond the standard model of elementary particles, requires the precision measurement of the change in the magnetic field. In the medical science, on the other hand, biomagnetism measuring apparatus, such as a magnetoencephalography (MEG), are active. The MEG measure the magnetic field and its change induced from the electrical activity of the brain and get the information about functional disorders of the brain. The MEG utilizes the superconducting quantum interference device (SQUID) as the magnetic sensor. Although the SQUID can measure the low magnetic field and its tiny change, its operation and maintenance entail enormous costs due to the production of the superconductive state. Thus, the highly sensitive magnetic sensor with the lower cost will have wide application area from the fundamental physics to the medical science.

Recently, an optical magnetic sensor based on the nonlinear magneto-optical rotation (NMOR) effects, which utilizes the interaction between atoms and coherence lights, is noticed. The features of the optical sensor are as follows. 1) The sensor has the potential to measure the magnetic field with the high sensitivity more than the SQUID. 2) The sensor can be operated at the room temperature. 3) Many sensors can be operated by one laser. 4) The sensor can be miniaturized by confining the atomic vapor in a glass cell. Thus, the optical magnetic sensor based on the NMOR would be useful tool for the study of the fundamental physics and medical science.