First generation atomic clock
Atoms are composed of nuclei and electrons. The electrons revolve around the nucleus at high speed and have different rotation orbits. Electrons have different energies on different rotating orbits. These energies are discontinuous and are called energy levels. Electrons can transition between different energy levels. When an electron transitions from a high "energy state" to a low "energy state", it will release electromagnetic waves. The frequency of this electromagnetic wave is what people call the resonance frequency. The resonance frequency of the same transition of the same atom is fixed, for example, a resonance frequency of cesium 133 is 9192631770 Hz. Since the resonance frequency is very stable, timing instruments made with it can be very accurate. The emergence of the atomic clock is a revolution in the history of human timekeeping. It makes the time measurement standard transition from the traditional macroscopic field of astronomy to a brand-new microscopic field. Since then, human time measurement and timing work has entered a new historical stage.
The elements currently used in the yard include hydrogen, cesium, and rubidium. The atomic clocks they make are named after these elements, such as cesium atomic clocks. For different purposes, different atomic clocks have been developed with different elements. Now the smallest atomic clock is only the size of a grain of rice, while the largest atomic clock is more than 5 meters in length; the cheapest atomic clock is about 10,000 yuan, and the most expensive atomic clock is worth more than 1 million yuan. These atomic clocks play a huge role in all walks of life.
In 1967, the 13th International Conference on Weights and Measures passed the definition that the duration of 9192631770 cycles of the transition radiation between the two hyperfine energy levels of the ground state of the cesium 133 atom without interference is 1 second, which is the atomic second.
my country began to study atomic frequency standards in the late 1950s. After 1960, the Shanghai Astronomical Observatory of the Chinese Academy of Sciences and the Beijing Institute of Electronics successively began to develop the ammonia molecular clock optically pumped sodium vapor chamber frequency standards. In the autumn of 1963, under the auspices of Professor Wang Yiqiu, Peking University cooperated with the 17th Institute of the Ministry of Electronics Industry to develop optically pumped cesium vapor chamber frequency standards, and completed three prototypes in 1965. After pairwise comparison, the stability is 5×10-11. This is my country's first atomic clock, and it has made important contributions to my country's national defense, aerospace, communications, and metrology.
Professor Wang Yiqiu also presided over the development of my country's first batch of mass-produced "optically pumped rubidium atomic clocks". This high-tech achievement played an important role in a number of national defense scientific research experiments. In 1978, it was awarded the Major Achievement Award by the National Science Conference. Professor Wang Yiqiu was awarded the 1993 Rao Yutai Physics Prize of the Chinese Physical Society for his pioneering long-term stability of the laser-pumped cesium beam frequency standard.
Development in the 1970s
In 1972, at the request of the Ministry of Electronics Industry, Peking University Hanzhong Branch resumed research on quantum frequency standards. In early 1973, under the organization of the Ministry of Electronics Industry, Peking University and the Ministry of Electronics Industry Beijing Dahua Radio Instrument Factory and State-owned 707 Factory jointly developed a mass-produced rubidium vapor chamber frequency standard. In the same year, Peking University resumed the major of spectroscopy and quantum science. Due to the urgent need of frequency standard talents at that time, the major was named "frequency standard major".
In 1973, the Shanghai Institute of Optics and Precision Instrument, Chinese Academy of Sciences, in cooperation with Guorong Lamp Factory, successfully developed the first domestic optically pumped rubidium vapor chamber frequency standard for desktop instruments. This is the first time that my country has put a domestic atomic clock into practice. At the same time, Chengdu Xinghua Instrument Factory cooperated with Peking University to produce rubidium atomic clocks in small batches. During this period, the cesium beam frequency standard prototype of the 17th and 12th Institute of the Ministry of Electronics Industry also achieved success. Prototypes of hydrogen masers developed by Shanghai Astronomical Observatory and Shanghai Metrology Bureau have also been successful. The Wuhan Institute of Physics, Chinese Academy of Sciences has also successfully developed a hydrogen maser and produced it in small batches.
On this basis, the National Atomic Clock Conference held in Beijing in 1976, led by the Chinese Academy of Sciences, made a comprehensive deployment for the development and production of national atomic clocks, and implemented the urgently needed frequency standard development and production tasks for various projects. The research tasks and production units identified at that time were: (1) Cesium beam frequency standard. The research and development units are the 12th and 17th Institute of the Ministry of Electronics Industry, Peking University, State-owned 4404 Factory and State-owned 768 Factory (under the Ministry of Electronics Industry). (2) Rubidium vapor chamber frequency standard. The production units are the State-owned 768 Factory and Peking University Hanzhong Branch, Shanghai Guorong Lamp Factory and the Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, State-owned 867 Factory, and the 27th Institute of the Ministry of Electronics Industry. (3) Hydrogen maser. Produced by the State-owned 4404 Factory and Wuhan Institute of Physics, Chinese Academy of Sciences.