Quantum Metrology Laboratory

Chief Scientist

Hidetoshi Katori

  • D. Eng.
  • Hidetoshi Katori
  • Brief resume
    Research Associate, Department of Applied Physics, University of Tokyo
    D.Eng., University of Tokyo
    Visiting Scientist, Max Planck Institute for Quantum Optics, Germany
    Associate Professor, Engineering Research Institute, University of Tokyo
    Professor, Department of Applied Physics, Graduate School of Engineering, University of Tokyo (-current)
    Research Director, ERATO Katori Innovative Space-Time Project, Japan Science and Technology Agency (-current)
    Chief Scientist, Quantum Metrology Laboratory, RIKEN (-current)


Quantum Metrology Laboratory

The quest for superb precision in atomic spectroscopy contributed to the birth of quantum mechanics and the progress of modern physics. Highly precise atomic clocks, which are one outcome of such research, are a key technology that supports our modern society, such as navigation with GPS and synchronization of high-speed communications networks. In 2001, we proposed a new atomic clock scheme, the “optical lattice clock,” which may allow us access to 18-digit-precision time/frequency in a measurement time of seconds. Armed with such high-precision atomic clocks, we investigate fundamental physics such as the constancy of fundamental constants and their coupling to gravity, as well as the application of such clocks to relativistic geodesy. In parallel, we explore quantum information technology and quantum metrology using “optical lattice clocks” as platforms to investigate the quantum feedback scheme and quantum simulator/computation.

Recent Research Topic

Investigation of new physics employing “optical lattice clocks” operated at the quantum limit.

Laser cooled and trapped strontium atoms
Fig. 1 Laser cooled and trapped strontium atoms

One second in the International System of Units (SI second) has been defined by the microwave transition frequency of a cesium atom since 1967. The SI second shares the 15-digit-uncertainty through the international atomic time. Seeking better time and frequency references, researchers began to develop “optical clocks” based on optical transitions of atoms in around 1980. A single ion confined in a Paul trap has been considered to be a promising candidate for an optical clock. However, in the 1990s, it became a practical concern that the quantum projection noise of a single ion would require a long averaging time to achieve its projected uncertainty.

In 2001, we proposed a new atomic clock scheme using optical lattices tuned to the “magic wavelength” that avoids a frequency shift caused by the optical trap (Fig. 2). This "optical lattice clock" allows the observation of 1 million atoms simultaneously, while the lattice potentials reduce Doppler shifts and atomic interactions by confining atoms in a three-dimensional lattice. As a consequence of employing a large number N of atoms, the quantum projection noise, the drawback of the single ion clock, is drastically reduced. In theory, the transition frequency of atoms can be measured with 10-18 uncertainty in an averaging time of seconds. In 2006, the clock using strontium atoms was adopted as one of the “secondary representations of a second,” which is a list of promising candidates for next-generation atomic clocks. The CIPM (Comité International des Poids et Mesures) recommended the transition frequency to be 429,228,004,229,873.7 Hz, whose uncertainty is limited solely by that of the SI second.

While significant reduction of the averaging time in clock operation was the prime motivation for developing optical lattice clocks, it had been left untouched so far. The frequency noise of lasers can be low enough to operate a single ion clock that has large quantum projection noise. In optical lattice clocks, however, because of their very low quantum projection noise of 1/√N, the fluctuation of excitation probability introduced by existing lasers becomes visible and significantly limits the clocks' performance. We have developed a technique to reject the influence of the frequency noise of the lasers by simultaneously interrogating the two clocks using a single laser. We demonstrated 17-digit frequency comparisons in the average time of 1,600 seconds (Fig. 3), achieving quantum projection noise limit stability corresponding to N ≈ ,000 atoms. This experiment, for the first time, demonstrated the design concept of the clock to increase stability by using a large number of atoms.

In timekeeping at the 10-18 uncertainty that optical lattice clocks will provide in the near future, clocks will read out the advance of time by placing them 1 cm higher on the Earth's surface. When such relativistic effects intervene in our daily motional scale and are detected in the time scale of seconds, a world reminiscent of the “melting clocks” in Dali's painting “The Persistence of Memory” will become a reality. Then the role of the atomic clock can be a probe for the curved space-time due to the gravity, rather than a tool for determining accurate time. Such sensitivities to gravitational potentials will find new applications in relativistic geodesy, to observe crustal movements and to search for resources underground.

The foundations of physics and atomic clocks implicitly assume the time- and space-invariance of fundamental constants. Among these is the dimensionless quantity known as the fine structure constant α (= e2/hc). Atomic clocks should keep the same time regardless of their constituent elements if α is constant, but the constancy of α is still a controversial issue. An interesting question is whether these clocks tick the same way as the others throughout the year as the gravitational potential from the sun changes. Precise comparisons of atomic clocks support such a challenge — that is, testing the coupling between electromagnetic constants (such as α) and gravity and the constancy of the fundamental constants — which may contribute to the experimental foundations toward a unified theory.

Schematic of an optical lattice clock
Fig. 2 Schematic of an optical lattice clock
(a) Atoms are separately trapped in optical lattice to prevent them from the Doppler effects and collisions. (b) This light shift perturbation does not alter the atomic transition frequency by giving the equal light shift for the two electronic states.
Stability of the optical lattice clocks
Fig. 3 Stability of the optical lattice clocks
(a) Frequency difference δν between two optical clocks operated at ν ≈ 29 THz. (b) Fractional frequency uncertainty δν/ν of the two clocks measured for asynchronous (open circles) and synchronous interrogations (filled circles).

Selected Publications

  1. H. Katori, Optical lattice clocks and quantum metrology, Nature Photon. 2011, 5, 203.
  2. M. Takamoto, T. Takano, H. Katori, Frequency comparison of optical lattice clocks beyond the Dick limit, Nature Photon. 2011, 5, 288.
  3. T. Akatsuka, M. Takamoto, H. Katori, Three-dimensional optical lattice clock with bosonic 88Sr atoms, Phys. Rev. A 2010, 81, 023402.
  4. H. Katori, K. Hashiguchi, E. Y. Il'inova, V. D. Ovsiannikov, Magic Wavelength to Make Optical Lattice Clocks Insensitive to Atomic Motion, Phys. Rev. Lett. 2009, 103, 153004.
  5. T. Akatsuka, M. Takamoto, H. Katori, Optical lattice clocks with non-interacting bosons and fermions, Nature Phys. 2008, 4, 954.
  6. H. Hachisu, et al. Trapping of Neutral Mercury Atoms and Prospects for Optical Lattice Clocks, Phys. Rev. Lett. 2008, 100, 053001.
  7. M. Takamoto, et al. Improved frequency measurement of a one-dimensional optical lattice clock with a spin-polarized fermionic 87Sr isotope, J. Phys. Soc. Jpn. 2006, 75, 104302.
  8. T. Kishimoto, et al. Electrodynamic trapping of spinless neutral atoms with an atom chip, Phys. Rev. Lett. 2006, 96, 123001.
  9. M. Takamoto, F. L. Hong, R. Higashi, H. Katori, An optical lattice clock, Nature 2005, 435, 321.
  10. H. Katori, M. Takamoto, V. G. Pal'chikov, V. D. Ovsiannikov, Ultrastable optical clock with neutral atoms in an engineered light shift trap, Phys. Rev. Lett. 2003, 91, 173005.

Core Members

Principal Investigator add delete
Hidetoshi Katori Chief Scientist    
Staff Scientist add delete
Masao Takamoto Research Scientist    
Postdoctoral Fellow add delete
Pierre Antoine Somnuck Thoumany Postdoctoral Researcher    
Manoj Das Postdoctoral Researcher    
Tomoya Akatsuka Postdoctoral Researcher    
Student Trainee add delete
Technical Assistant add delete
Administrative Assistant add delete
Visiting Research Staff add delete
Other Staff add delete
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