Precise Optical Atomic Clock Starts Ticking

“Standards. Readings from the two standards enable us to fine-tune the 'ticking' of the clock as a whole with significantly greater precision," Dr. Michal Zawada from the University of Warsaw said.

Both atomic standards in Poland’s National Laboratory (KL FAMO) system operate with strontium 88 atoms, but in order to exclude repetitive errors, in one of them strontium 87 atoms can be used as well. The strontium atoms in each standard are isolated from the environment and from one another: cooled to a temperature below 10 microkelvins, they are situated inside an ultrahigh vacuum chamber and immobilized in a specially constructed optical trap generated by the beam of a supplementary laser.

To read the passage of time off the strontium atoms, they are exposed to the red light of the main, ultra-stable laser, with a frequency of approx. 429 terahertz. After the energy of the laser light is fine-tuned to match the transition in the atoms, the frequency of the laser beam is translated by means of the optical frequency comb into radio frequencies, at around 250 megahertz. At this stage the individual "ticks" of the clock are counted by the corresponding electronic apparatus.

"The stability of such a clock is one thing, whereas its precision is something else. To ascertain the latter, in other words to be able to compare our readings to those of the existing time standards, we have started a collaboration with the Central Office of Measures in Warsaw and the Borowiec Astrogeodynamic Observatory," Prof. Czeslaw Radzewicz from the UW Faculty of Physics said.

Time signals are transmitted between the laboratories in Toruń, Warsaw, and Borowiec via fiber-optic cables made available by the PIONIER academic network and the telecoms company Orange, under the OPTIME project financed by the National Centre for Research and Development. The network consists of telecommunications fiber-optic cables and dedicated transmission and amplification equipment developed by engineers from the Department of Electronics at University of Science and Technology in Cracow.

High-precision time measurements play an important role in many fields of science and technology.

The most advanced clocks can help physicists to test such fundamental aspects of reality as the time variability of physical constants, to very precisely verify the predictions of the general theory of relativity, and also to search for dark matter in the Universe. Atomic clocks of the previous generation, with significantly lower precision, are currently being used in applications including satellite navigation systems, high-capacity wireless networks (wi-fi), ensuring the security of bank communications, and also taking measurements of the Earth's gravitational field, yielding insight into its internal geological structure.