【Young Faculty:033】Ichiro Ushijima, Lecturer : Katori・Ushizima lab, Department of Applied Physics.

2009: B.S., Department of Physics, The University of Tokyo
2011: M.S., Department of Applied Physics, The University of Tokyo
2014: Dr. Eng., Department of Applied Physics, The University of Tokyo
2014: Postdoctoral Fellow, Quantum Metrology Laboratory, RIKEN
2016: Postdoctoral fellow, RIKEN Center for Advanced Photonics, RIKEN
2017: Assistant Professor, Department of Applied Physics, The University of Tokyo
2020: Lecturer, Department of Applied Physics, The University of Tokyo

【About the Research】
Clocks play a major role in social infrastructure, such as GNSS (Global Navigation Satellite System) including GPS, synchronizations of high-speed communications as 5G (5th Generation), and the calibration of precision equipment. We study “optical lattice clocks”, which is proposed by Prof. Katori as a new atomic clock scheme in 2001. Our research has allowed optical lattice clocks to reach an accuracy within a second at the age of the universe (about 13.8 billion years).
As long as we live normally, I think that such high accuracy of clock may be needed. In recent years, we use the ultra-high accuracy clock as a tool to measure a changing value around me for practical use. For example, according to Einstein's theory of relativity, a clock at a high place advances time faster than a clock at a low place. Optical lattice clocks can measure the time lag due to the height difference of only 1 cm. This relativistic geodesy measures the difference in gravitational potential as the difference in time advance.
We have developed optical lattice clocks at the University of Tokyo and RIKEN respectively, and demonstrated the relativistic geodesy to measure the time difference between the two clocks induced by a height difference of about 15 m. In addition, two clocks have set on the 450 m observatory floor and on the ground in TOKYO SKYTREE, and we have tested the gravitational redshift for the verification of the theory of relativity.
By using the optical lattice clock as a precise gravitational potential meter, it is expected that the precursors of an earthquake, the eruption of a volcano and the arrival of a tsunami can be observed. The optical lattice clock is not just a high-precision clock, but an interesting clock that has the potential to create new lifestyles.

Figure: Optical lattice clocks

(1) M. Takamoto, I. Ushijima, N. Ohmae, T. Yahagi, K. Kokado, H. Shinkai and H. Katori, Nature Photonics 14, 411-415 (2020).
(2) I. Ushijima, M. Takamoto and H. Katori, Phys. Rev. Lett. 121, 263202 (2018).
(3) T. Takano, M. Takamoto, I. Ushijima, N. Ohmae, T. Akatsuka, A. Yamaguchi, Y. Kuroishi, H. Munekane, B. Miyahara and H. Katori, Nature Photonics 10, 662-666 (2016).
(4) I. Ushijima, M. Takamoto, M. Das, T. Ohkubo and H. Katori, Nature Photonics 9, 185-189 (2015).

【Future aspirations】
Higher precision atomic clocks are expected to contribute not only to engineering applications but also to fundamental physics. A number of theoretical studies, that a dark matter can be detected by using atomic clocks, have recently been published. I would like to work with students and collaborators on new research that can contribute to such progress in physics using the techniques learned from the development of atomic clocks.

Lab :

【Press Release】