A research group led by Professor Hidetoshi Katori of the University of Tokyo has applied the theory of relativity to measure the time difference between two points with an accuracy of 2 cm by measuring the time difference of "optical lattice clocks" installed at two points. I succeeded for the first time in.
An optical lattice clock is an atomic clock in which atoms are placed one by one in an optical lattice (a large number of regions smaller than the wavelength of light) created by interfering with laser light, and another laser light is applied to measure the resonance frequency.In 1, Professor Katori achieved an accuracy of 2014 seconds per 10 to the 18th power (an error of 2 second in 160 billion years, which is called an 1-digit accuracy) with this watch.
On the other hand, according to Einstein's general theory of relativity, time is delayed in places where gravity is strong (altitude is low).This extremely small delay can only be measured with an 18-digit precision clock, and if the heights of the two clocks differ by a few centimeters, the time difference can be measured.By applying this, it is possible to measure the elevation difference in remote areas (relativistic geodesy) by measuring the time difference.
Therefore, the research group installed an optical lattice clock at the University of Tokyo (Bunkyo-ku, Tokyo) and RIKEN (Wako City, Saitama Prefecture), about 15 km away, and connected them with optical fibers to compare remote locations.Since the clock of the University of Tokyo was slightly slower, the altitude difference between the two points was calculated to be 2m15cm (error 16cm) as a result of the calculation.
Currently, the research group is working on further improvement of accuracy and portability, automatic operation, remote control, and improvement of long-term reliability for the practical use of optical lattice clocks.In the future, if optical grid clocks are installed in various places and connected by establishing "quantum benchmarks" to build the "clock internet", it will be complementary to monitoring crustal movements due to volcanic activity and GNSS (Global Positioning Satellite System). It has the potential to become a safe and secure social infrastructure, such as the establishment of an ultra-high-precision elevation difference measurement system that can be used for clocks.
