2026 Recipients of C&C Prize
Group A
Dr. Hidetoshi Katori Professor, Department of Applied Physics, Graduate School of Engineering, The University of Tokyo |
Citation
Pioneering Contributions to the Realization of the Optical Lattice Clock
Achievements
Precise time measurement is a fundamental technology that underpins modern information and communications technology (ICT) society, including information and communications networks, global navigation satellite systems (GNSS), electronic transactions, and scientific measurements. The current definition of the “second” is based on the cesium atomic clock, which uses the frequency of microwaves absorbed and emitted by cesium-133 atoms as its standard. On the other hand, by utilizing optical transitions in atoms—which have frequencies approximately 100,000 times higher than those of microwaves—time can be divided into finer intervals, offering the potential to significantly improve the accuracy of clocks. Against this backdrop, research and development of optical atomic clocks has been advancing. Dr. Hidetoshi Katori proposed the concept of the optical lattice clock and, by actually realizing it, established an ultra-high-precision time standard that far surpasses conventional atomic clocks. Furthermore, he extended these results to relativistic geodesy and spacetime sensing, paving the way for applications in next-generation information and communications, quantum technology, and precision positioning.
In conventional optical atomic clocks using a single ion, it was difficult to achieve both high precision and short-duration measurements. To improve statistical precision, repeated measurements were necessary, requiring a single charged atom—cooled to near absolute zero—to be trapped between electrodes and measured multiple times. To overcome this limitation, Dr. Katori proposed the concept of the optical lattice clock in 2001 and successfully conducted fundamental experiments in 2003. In an optical lattice clock, a large number of strontium atoms are trapped within an optical lattice—a periodic structure formed by standing waves of light created by the interference of opposing laser beams. The optical lattice suppresses the Doppler effect caused by the thermal motion of the atoms and allows for the simultaneous observation of a large number of atoms. However, optical atomic clocks faced the challenge that the laser light used to trap the atoms could alter the frequency of the clock transition. Dr. Katori proposed and demonstrated that this effect could be counteracted by forming the optical lattice at a specific wavelength—the “magic wavelength”—at which the electric polarizabilities of the ground state and excited state are equal. Furthermore, by observing a large number of atoms simultaneously using this method, he established a technique to reduce quantum noise. In 2015, he reported in Nature Photonics the achievement of 10-18-level precision in optical lattice clocks, approximately three orders of magnitude better than the 10-15-level precision of conventional cesium atomic clocks. This level of precision corresponds to a timing error of only about one second over more than 10 billion years. These achievements made it possible to simultaneously achieve high precision and short-time measurements in atomic clocks, laying the foundation for the advancement of optical lattice clock research and development around the world. Optical lattice clocks have been established as a new time standard technology in the fields of atomic physics and quantum metrology. Furthermore, in 2006, the International Committee for Weights and Measures (CIPM) adopted the optical transition of the strontium-87 atom as one of the secondary representations of the “second,” and the strontium optical lattice clock has become one of the leading candidates for the redefinition of the “second,” which is currently under international discussion for a possible redefinition of the second around 2030.
Dr. Katori has developed optical lattice clocks not merely as time standards, but as a new measurement technology. According to the general theory of relativity, clocks run at different rates in locations with different gravitational potentials. Optical lattice clocks with 10-18-level precision can detect these extremely small differences. Dr. Katori and his team installed two optical lattice clocks—one on the ground floor of Tokyo Skytree and the other at the observation deck, approximately 450 meters above ground—and compared their clock frequencies. They demonstrated that the clock at the observation deck ran slightly faster than the one on the ground and published their findings in 2020. This achievement marked a significant step toward the practical application of relativistic geodesy, which measures differences in altitude and gravitational potential based on variations in clock frequency. It also demonstrated that optical lattice clocks can serve as high-performance sensors for measuring height differences and gravitational potential differences, paving the way for spacetime sensing to monitor crustal movements and volcanic activity.
Furthermore, Dr. Katori promoted research and development toward practical deployment of optical lattice clocks. Dr. Katori’s research group miniaturized and made more robust the physical package for spectroscopically analyzing atomic clock transitions and the laser control system, reducing the size of the apparatus—which had been approximately 920 liters in the Tokyo Skytree experiment—to about 250 liters. In 2025, based on these achievements, Shimadzu Corporation commercialized the world’s first optical lattice clock. Furthermore, in 2026, the International Bureau of Weights and Measures (BIPM), RIKEN, and Shimadzu Corporation signed a memorandum of understanding to explore the role of transportable optical frequency standards. As a result, optical lattice clocks are being implemented in society not only as time standards but also as infrastructure utilized in a wide range of fields, including information and communications, precision measurement, and geodesy.
Dr. Katori’s achievements span the proposal and demonstration of the principles behind ultra-high-precision optical lattice clocks, their application to relativistic geodesy and spacetime sensing, and their practical implementation for societal deployment. These contributions significantly advance the information and communications technologies that underpin precise control, positioning, and synchronization, and serve as a prime example of C&C technology—a highly integrated fusion of high-stability lasers, photonics, electronic control, and vacuum and cooling technologies. These achievements can be highly regarded as outstanding accomplishments worthy of the C&C Prize.