Ryoichi Higashi

An optical lattice clock.

The precision measurement of time and frequency is a prerequisite not only for fundamental science but also for technologies that support broadband communication networks and navigation with global positioning systems (GPS). The SI second is currently realized by the microwave transition of Cs atoms with a fractional uncertainty of 10-15 (ref. 1). Thanks to the optical frequency comb technique, which established a coherent link between optical and radio frequencies, optical clocks have attracted increasing interest as regards future atomic clocks with superior precision. To date, single trapped ions and ultracold neutral atoms in free fall have shown record high performance that is approaching that of the best Cs fountain clocks. Here we report a different approach, in which atoms trapped in an optical lattice serve as quantum references. The ‘optical lattice clock’ demonstrates a linewidth one order of magnitude narrower than that observed for neutral-atom optical clocks, and its stability is better than that of single-ion clocks. The transition frequency for the Sr lattice clock is 429,228,004,229,952(15) Hz, as determined by an optical frequency comb referenced to the SI second.

Improved Frequency Measurement of a One-Dimensional Optical Lattice Clock with a Spin-Polarized Fermionic 87Sr Isotope

We demonstrate a one-dimensional optical lattice clock with a spin-polarized fermionic isotope designed to realize a collision-shift-free atomic clock with neutral atom ensembles. To reduce systema...

Frequency measurement of a Sr lattice clock using an SI-second-referenced optical frequency comb linked by a global positioning system (GPS)

We have established a transportable frequency measurement system using an optical frequency comb linked to a commercial Cs atomic clock, which is in turn linked to international atomic time (TAI) through global positioning system (GPS) time. An iodine-stabilized Nd:YAG laser is used as a flywheel in the frequency measurement system. This system is used to measure the absolute frequency of the clock transition of (87)Sr in an optical lattice. We obtained a fractional uncertainty of 2x10(-14) in the frequency measurement with a total averaging time of ~ 10(5) s over 9 days.

Engineering Stark Potentials for Precision Measurements: Optical Lattice Clock and Electrodynamic Surface Trap

Employing the engineered electric fields, we demonstrate novel platforms for precision measurements with neutral atoms. (1) Applying the light shift cancellation technique, atoms trapped in an optical lattice reveal 50‐Hz‐narrow optical spectrum, yielding nearly an order of magnitude improvement over existing neutral‐atom‐based clocks. (2) Surface Stark trap has been developed to manipulate scalar atoms that are intrinsically robust to decoherence.

A NOx and SO2 gas analyzer using deep-UV and violet light-emitting diodes for continuous emissions monitoring systems

A nitrogen oxides (NOx) and sulfur dioxide (SO2) gas analyzer using deep ultraviolet (DUV) and violet light- emitting diodes (LEDs) is developed. The LEDs with wavelengths of 280 nm and 400 nm were alternately turned on to detect SO2 and nitrogen dioxide (NO2) absorption. Nitric oxide (NO) was converted to NO2 with an ozonizer. In order to reduce water interference caused by water adsorption onto an inner surface of a gas ow cell, collimating optics reducing re ected lights were designed. As a result, less than 1% by full scale (%F.S.) of uctuation, 2%F.S. of drift and 0.5%F.S. of water interference were achieved in 0-50 ppm concentration range. Conversion efficiency from NO to NO2 was over 95%.

Frequency Measurement of an Optical Lattice Clock

A frequency measurement system is developed away from a National Metrological Institute with a frequency link to International Atomic Time (TAI). The absolute frequency of the ¹S₀ -³P₀ clock transition of the ⁸⁷Sr lattice clock is determined to be 429,228,004,229,875(4) Hz. The frequency measurement system is being further improved by introducing an optical fiber link and by upgrading the GPS link.

Precise time and frequency transfer link used for the uncertainty evaluation of Sr. optical lattice clock

The recent development of optical frequency standards has been performed quite rapid and the better uncertainty than that of microwave frequency standards will be realized in very near future. We are evaluating a one-dimensional 87Sr optical lattice clock developed and located at the University of Tokyo, Tokyo, by using UTC(NMIJ) generated at NMIJ, Tsukuba. The baseline length between those two sites is about 50 km. We constructed a time and frequency transfer link using GPS carrier phase method for this link. We use GIPSY software and a newly developed one for data analysis. Our developed one works in real time using carrier phase data and broadcast navigation data which are obtained from the carrier phase receivers.