Department of Applied Physics, Graduate School of Engineering, The University of Tokyo / RIKEN
“Making optical lattice clocks compact and useful for real-world applications”
Hidetoshi Katori is a Professor in the Department of Applied Physics, Graduate School of Engineering, The University of Tokyo, a Chief scientist, Quantum Metrology Laboratory, RIKEN, and a Team Leader of Space-Time Engineering Research Team, RIKEN Center for Advanced Photonics. His research interests cover Atom Molecular and Optical Physics and Quantum Metrology. He proposed an optical lattice clock in 2001 and demonstrated the clocks with a fractional uncertainty of 10^-18 in 2014. He is exploring novel applications enabled by such highly accurate atomic clocks. He is the recipient of a European Time and Frequency Award (2005), Rabi Award (2008), Japan Academy Award (2015), Leo Esaki Prize (2017), Micius Quantum Prizes (2020), and Breakthrough Prize in Fundamental Physics (2022).
An “optical lattice clock” proposed in 2001 benefits from a low quantum-projection noise by simultaneously interrogating many atoms trapped in an optical lattice. The essence of the proposal was an engineered perturbation based on the “magic wavelength” protocol, which has been proven successful up to 10-18 uncertainty. About a thousand atoms enable such clocks to achieve 10-18 stability in a few hours of operation. This superb stability is especially beneficial for chronometric leveling, which enables determining the height difference of far-distant clocks connected by telecom fiber with an uncertainty of 1 cm by the gravitational redshift of the clocks. We overview the progress of optical lattice clocks and address recent topics to explore real-world applications of the 18-digit-accurate clocks, including 1) compact optical lattice clocks under development in collaboration with industry partners, 2) demonstration of an on-vehicle optical clock, and 3) our challenge to further improve the stability of the clocks by “longitudinal Ramsey spectroscopy” that allows continuous interrogation of the clock transition.
Department of Physics & Astronomy, Seoul National University
Kyungwon An received his BS and MS in physics from Seoul National University, and his PhD from Massachusetts Institute of Technology working with Michael S. Feld on realizing the first single-atom laser. He stayed at MIT as a postdoc and then a research scientist until 1998. He then moved to Korea Advanced Institute of Science and Technology and stayed there as a physics professor until 2001. Since then, he has been a physics professor at Seoul National University, where he has been performing various experiments on nonclassical field generation in an atom-cavity system as well as quantum chaos and non-Hermitian physics in microcavity lasers. He received Vinci d’Excellence Award in 1995, Outstanding Young Researcher Award from the Association of Korean Physicists in America in 1996 and Young Scientist Award from the Korean Ministry of Science and Technology in 1999 for the development of the first single-atom laser. He received Education Award of Seoul National University in 2011 for implementing technology-enabled active learning in undergraduate physics courses. He received Atomic and Molecular Physics Award from the Korean Physical Society in 2018, Sung-Do Optical Science Award from the Korean Optical Society as well as National Academy of Sciences Award in 2021 for his work on coherent single-atom superradiance.
A superradiant state is a phase-correlated quantum state of atoms capable of undergoing superradiance immediately without a time delay. We can prepare a superradiant state in an optical cavity by exciting N atoms in the same superposition state of the ground and excited states with the same phase angle by using a nanohole array aperture. These correlated atoms generate superradiance in the cavity even when the mean number of intracavity atoms is much less than unity. As an application, the superradiant state can be used to realize the long-sought superabsorption, the opposite of superradiance, by reversing the superradiance process in time through the phase control of the superradiant state. As another application, we can also realize a photonic quantum engine, where the atoms entering the cavity act as a heat reservoir and the photons are an engine medium exerting radiation pressure on the cavity mirrors. Our engine operates between a thermal state and a superradiant state of reservoir at the same reservoir temperature. In our experiment, the effective engine temperature rose up to 150,000K because of the large ergotropy transfer from the reservoir through superradiance, resulting in the engine efficiency as high as 98%, the highest ever achieved in quantum engines.
Earthquake Research Institute in the University of Tokyo / National Research Institute for Earth Science and Disaster Resilience
“Pioneering seafloor seismic observations using distributed acoustic sensing technology”
Masanao Shinohara is a professor of marine seismology at the Earthquake Research Institute in the University of Tokyo, and a technical director in National Research Institute for Earth Science and Disaster Resilience as a cross appointment. He is also the chair of Japan chapter, Institute of Electrical and Electronic Engineers (IEEE) Oceanic Engineering Society at the present. He has over 30 years of research and development experience in the areas of the marine seismology and geophysics. His research into earthquake generation and the structure of the Earth has contributed to the development of new observation apparatuses at the marine environment. He was the recipient of Honorable Mention for Best Paper in Geophysics in 2018 for his pioneering research at development of an underwater gravity measurement system that uses an autonomous underwater vehicle. Free-fall pop-up type long-term ocean bottom seismometers developed by his team are one of the most successful seafloor seismic observation system in the world. His current research interests include application of optical fiber sensing technology to seafloor seismic observation. He attempts to perform a seismic observation using the Distributed Acoustic Sensing technology with phase measurement by interferometry on a seafloor optical cable system.
A seismic observation using Distributed Acoustic Sensing measurement (DAS) is attractive because spatially high-density data along a fiber can be obtained for a long distance. DAS measurement with interferometry of scattering waves becomes increasingly accurate. Because there are still fewer seismic stations in marine area, DAS measurement using seafloor cables is effective to increase the number of seismic stations. The University of Tokyo deployed a seafloor seismic tsunami observation system using an optical fiber cable off Sanriku in 1996. We have performed nine temporary DAS measurements since February 2019 using spare fibers of the Sanriku system. Each observation periods were from a few days to more than a month. A total length of the measurement reached 100 km with observational interval of less than 10 m. As a result of the observations, many earthquakes including micro-earthquakes and teleseismic events could be observed. The noise levels of the DAS measurement were comparable to those of conventional seismometers. In this presentation, observations using DAS technology on an actual seafloor cable and scientific results from the DAS data will be introduced and a performance of DAS measurement will be discussed from a point of view of earthquake observation.