A Chinese team of scientists has developed an extremely precise optical clock that loses or gains one second every 7 billion years. Using ultra-cold strontium atoms and powerful laser beams, the team at the University of Science and Technology of China created a clock with stability and uncertainty under 5 quintillionths. The achievement makes China only the second country in the world after the U.S. to achieve such precise timekeeping. It also lays an important foundation for the establishment of a global optical clock network, the team, led by physicist Pan Jianwei, wrote in the peer-reviewed journal Metrologia earlier this month. In addition, they said it opened up new pathways to test fundamental physics theories, detect gravitational waves and search for dark matter.
The current most precise strontium-based optical clock is housed at the University of Colorado in Boulder, developed by a group led by Chinese-American physicist Jun Ye. It remains slightly more accurate than its Chinese competitor and its operation is more stable. Other players in the race include the University of Tokyo and the Institute of Physical and Chemical Research in Japan, and the National Metrology Institute of Germany. Optical clocks hold great potential for applications in critical infrastructure in the future. They could significantly enhance the precision of global navigation satellite systems, and help build highly secure communication networks based on quantum key distribution. They could also improve the synchronization and efficiency of power grids, and play a vital role in national defense and security.
Today, the definition of a second is based on the microwave fountain clock, a type of atomic clock. It works by releasing cesium atoms upwards, which then fall under gravity in a fountain-like motion while they are excited with microwave pulses. Their electrons then absorb and emit light particles to jump between different energy levels. By counting such cycles as “ticks” that mark fractions of a second, scientists can achieve high-precision timekeeping with stabilities of several quadrillionths. But the precision of a microwave clock is limited by the microwave frequency standard. In recent years, researchers have built optical clocks which use laser light to drive electronic transitions and achieve performances two orders of magnitude better than their microwave counterparts. However, if microwave clocks are to be replaced by optical ones for the future definition of time, at least three laboratories in the world will need to have an optical clock with stability below 5 quintillionths and uncertainty below 2 quintillionths, the South China Morning Post reports.
