The generation and maintenance of time and the transmission of time information through certain ways are called "time service". Since the 1960s, generations of time givers in China have been rooted in the northwest, willing to sit on the bench, making innovations and self-improvement, creating an accurate "Chinese time"—— Inscription In Lintong District, Xi'an, where the world-famous terracotta warriors and horses of Qin Shihuang are located, the subway from the main urban area of Xi'an from west to East turns northward at an almost right angle after arriving at HuaQingChi station. Part of the reason is to avoid the national time service center of the Chinese Academy of Sciences about two kilometers away from the East, so as not to affect China's national standard time - Beijing time, which is generated and maintained here. At the beginning of the establishment of its predecessor, Shaanxi Observatory, the national time service center of the Chinese Academy of Sciences was mainly established to meet the urgent needs of national defense and economic construction. Today, Zhang Shougang, director and chief scientist of the national time service center of the Chinese Academy of Sciences, and his "time team" have achieved a number of key core technological breakthroughs, reducing the deviation between China's standard time and the international standard time from 100 nanoseconds to 5 nanoseconds, making its overall performance in the forefront of the world and engraved the national interests into the "sea of stars". Strive to build a "Chinese clock" Under the mezzanine of Zhang Shougang's desk, there is a white T-shirt printed with the pattern of a barrel shaped precision device. "The T-shirt was customized by my colleagues when I graduated from the Paris Observatory in France. The device on the picture is the world's first cesium atomic fountain clock I participated in the transformation." He said. Among the seven basic physical quantities in the international system of units, time is the most accurate and widely used one. In 1967, in order to improve the accuracy of time measurement, the 13th International Conference on Metrology revised the definition of time unit "second" to change the astronomical time "second" reflecting the earth's rotation state to the atomic time "second" timed by the electromagnetic oscillation cycle inside the atom. Since then, some physicists have worked hard to develop an atomic clock related to the generation and maintenance of time, that is, the atomic frequency standard (frequency standard), which is not only a strategic resource for a country's scientific advancement of time and frequency, but also a manifestation of national sovereignty. Physicist Wang Yiqiu, a former executive vice president of Peking University, said: "in the era of precision strike, the role of atomic clock is no less than that of atomic bomb." "In 1998, a well-known physicist from western countries visited China and said that the experimental research of China's atomic clock depends on 'taking a chance'. I learned this sentence in a chat with other researchers in the laboratory. I was deeply stimulated and determined to make a primitive clock with long Chinese ambition." Zhang Shougang said. In 2005, Zhang Shougang left Beijing after returning home from overseas study and came to the national time service center in Lintong District, Xi'an to preside over the research and development of atomic clock and standard time. "At that time, the small cesium clock used by the national time service center for punctuality completely depended on imports, and there was no benchmark cesium atomic fountain clock, even relevant research equipment and researchers." According to Guo Wenge, a researcher of the national time service center who returned from Zhang Shougang's University Alumni almost at the same time, it is under such conditions that Zhang Shougang started from a person, a basement of his unit and a screwdriver to build a platform and recruit talents. Now, the quantum frequency standard laboratory of the national time service center established by him has nearly 100 young and middle-aged researchers, and has developed into a Key Laboratory of the Chinese Academy of Sciences; It has not only independently developed the internationally advanced benchmark cesium atomic fountain clock, but also realized the commercialization of the punctual optically pumped small cesium clock in 2018. The widely used portable small cesium clock products were monopolized by the United States for more than 50 years. In 2017, small cesium clock products were successively banned from sale to China. Today, this domestic small cesium clock has not only been used in Beidou satellite navigation system, changhe-2 navigation system, 5g communication system and Arctic scientific research, but also equipped in the national standard time generation and maintenance system. In November 2021, three domestic small cesium clocks obtained the contribution weight in the calculation of international standard time, and were recommended by the International Bureau of weights to countries for the generation of standard time. "The foreign scientist who said that China depends on 'chance' expressed his admiration for China's achievements in time-frequency field when he met me at an annual academic conference in 2019." Zhang Shougang said. The responsibility and responsibility of consecrating the red blood Like Zhang Shougang's T-shirt, it has been in his office for several years, and there are four bottles of champagne. He brought it back from France. At first, he was ready to celebrate with everyone after a major breakthrough. But until now, even if they have made more scientific research breakthroughs, the celebration wine has not been opened. Zhang Shougang said that it is not that there is no work to celebrate, but that there is a dial in the heart of the time giver: in the endless pursuit of accuracy and stability performance, the end point of each payment will become a new starting point again and again. In modern China, the generation and transmission of standard time was dominated and controlled by foreigners for a long time. After the founding of new China, with the start of large-scale national defense and economic construction, there is an urgent need to build a time desk in a hidden place in the inland hinterland. Under the care of Premier Zhou Enlai, the Shaanxi Observatory, located in Pucheng County, Shaanxi Province, was built in 1966 and started short wave time service in 1971. Many scientists and young college students from big cities such as Beijing, Shanghai and Nanjing participated in the establishment of Shaanxi observatory. Qi Guanrong, a former director of the Shaanxi Observatory, recalled that when he just graduated from Nanjing University, he got off the train with the first batch of more than a dozen other young people and turned to the car. After getting off the car and walking, he arrived at the foot of Jinqi mountain in Pucheng County, which is far away from the crowd. Recalling the barren and grassy construction site in front of us at that time, Qi Guanrong said: "even if you are carrying stones, you should build the observatory with your hands!" The completion of short wave time service station has enabled China to have land-based radio time service capability covering the whole territory, turning a new page in China's time service. On this basis, the low-power test-bed of long wave time service station was trial broadcast in July 1976. Four months later, the signal was officially transmitted regularly every day. "Building a national clock... Is important not only for cutting-edge technology, but also for the development of China's natural science and even the whole science." Qian Xuesen once described the significance of long wave time service. The completion of the long wave time service system has enabled China to catch up with the world. This achievement also won the first prize of the national science and Technology Progress Award in 1988. In the construction of an independent time service system, a number of young and middle-aged scientific and technological workers have taken root in the West and serve the country through science and technology. In order to further meet the national requirements for time service, Shaanxi Observatory moved to Lintong in 1980 and changed its name to the national time service center of the Chinese Academy of Sciences in 2001. Although the address and name have changed, the original intention has not changed. The time givers of the new era continue to have red blood and are persistent in research and dedication. Atomic clock is the crystallization of cutting-edge theory and technology. It is normal to build an atomic clock in ten years or more. Sometimes it's not just physical pain that people suffer from: some are sedentary, suffer from lumbar disc herniation and don't have time to have surgery, some have ankle fractures in plaster and jump into the laboratory on crutches during the Spring Festival holiday; But more, it is the pain of "staying together" with hundreds of parts and instruments. The optical clock is a forward-looking atomic clock. Chang Hong, a researcher at the national time service center, is responsible for the development of strontium atomic optical clock. In the key stage of scientific research, as the only child in his family, he has experienced his parents' death due to illness, of which his father had been paralyzed for six years before his death. "In the past, I was most afraid of receiving a phone call at night and saying that there was something wrong with the elderly at home." But he said that in this strategic highland that the whole world is staring at, if you want to seize it, the time window is only one or two years. The national plan cannot be delayed here. No matter how difficult it is, we have to bite our teeth and push the research down. "Clock making is a career worth a lifetime, because it is the strategic demand of the country; clock making is also a career that can't be done in a lifetime, because the development and progress of all walks of life have endless requirements for the performance of atomic clock, including the convenience of use." Zhang Shougang said. He has been working on this new type of atomic clock for 31 years. Innovate and constantly climb the world's scientific and technological peak The effective operation of communication, electric power, finance, navigation and other systems with pulsating economic and social development depends on high-precision time synchronization. With the development of society and the progress of science and technology, the time service system is not only a public welfare project related to the national economy and the people's livelihood, but also a strategic instrument related to national security. In 2003, in order to meet the major needs of the country, relying on the accumulation of time-frequency technology and astronomical science theory, the national time service center and relevant research institutes developed and built the demonstration and verification system of China's regional positioning system (CAPS) in less than three years, with an accuracy no less than that of the US GPS satellite navigation system. "The construction of caps system reflects the spirit of 'being brave in innovation' and is still encouraging people to move forward in the new era." Dou Zhong, Party Secretary of the national time service center of the Chinese Academy of Sciences, said that innovation is the first driving force leading scientific and technological progress. Since the 18th National Congress of the Communist Party of China, the national time service center has adhered to continuous and rapid innovation, and strengthened the layout, strength and expansion in the areas of national strategy. Sending an optical clock with higher precision than a microwave atomic clock into space and realizing a high-precision space-time benchmark is the forefront of the current development of science and technology in the world. Zhang Shougang and more than a dozen young and middle-aged "Clockmakers" in his team have built the first ground optical clock in the center in ten years. Now, their work is to plug this optical clock with more than 20 square meters into the experimental cabinet of the space station with less than 1 cubic meter. The difficulty is not only the reduction of the size of the components, but also the reconstruction of the system and process, which needs to break through a series of key technologies. At present, this "striving clock" is stepping up its development in the national time service center. "The national time service center has made great progress in time and frequency research and time service. It is because of these lovely colleagues." Zhang Shougang said that "National People" do "national affairs" and "national teams" assume "national responsibilities". The national time service center always puts national interests first and is committed to filling one domestic gap after another: —— Restart the independent measurement of the strategic resource of world time, get rid of the dependence of previous world time data on foreign countries, and ensure the smooth progress of China's space mission. —— Start the construction of high-precision ground-based time service system, combine optical fiber time service with improved long wave time service to form ground-based time service, and integrate with satellite time service to build a time service system integrating heaven and earth. —— Develop new technologies for network time transmission and application, establish nodes in the cloud and establish a network time service system to fill the vacancy of high-precision "Beijing time" in cyberspace. …… "Where national interests expand, our time service will follow." Zhang Shougang said that timekeepers will continue to be red blooded, carry forward the spirit of "two bombs and one satellite" and the spirit of older generation scientists, adhere to independent innovation, lead high-quality development, and make greater achievements in time service in the new era. (Xinhua News Agency)