The Global Positioning System (GPS), which provides location information by transmitting signals from satellites, is used in vehicle navigation, aircraft, and ship operations. It is now widely used in civilian applications, but in the early 1990s, it was primarily utilized by the military for operating fighter jets and missiles. GPS is a Global Navigation Satellite System (GNSS) provided by the United States. Currently, in addition to the U.S. (GPS), Russia (GLONASS), Europe (Galileo), and China (Beidou) are establishing their own GNSS.

The heart of GPS is the clock. GPS calculates distance and position based on the time it takes for signals to reach a location. The accuracy of the measurement depends on how precisely time is provided. GPS satellites are equipped with atomic clocks that deliver precise time. In military operations that guide missiles and involve time-sensitive cyber warfare, time is gold. Recently, China announced the development of a precise atomic clock that could fundamentally change the landscape of future warfare. The United Kingdom also disclosed that its previously secret defense research agency developed a military-grade atomic clock using quantum technology. Competition to secure accurate and precise time in the defense sector is spreading.

◇Outdoor atomic clocks loaded onto military trucks

High-precision timekeeping systems, including atomic clocks, have emerged as the center of modern warfare. Accurate time information is essential to efficiently operate radars that detect stealth fighters thousands of kilometers away. During the China International Aviation and Aerospace Exhibition held in Zhuhai last November, visitors examine the displays of the J-20S (right) and J-35A (left) fighters at the booth of Aviation Industry Corporation of China (AVIC). /EPA Yonhap

On the 18th (local time), researchers from China's Institute of Measurement and Testing Technology and Advanced Tracking Technology Innovation Center announced the development of a small cesium atomic clock (NIM-TF3) the size of a compact refrigerator, measuring 1.5 meters.

Countries around the world have precise atomic clocks to maintain a consistent standard of time. An atomic clock operates based on the vibrations of electrons in an atomic shell. It measures time by counting the number of vibrations of the electrons. Most atomic clocks use the stable isotope cesium. The internationally recognized length of one second is defined by cesium atomic clocks.

Atomic clocks are usually operated in specially designed research facilities that are insulated from environmental influences. Researchers explained that the newly developed clock is compact enough to be loaded onto a truck and robust enough to function normally during long-distance transport. It maintains precision of less than 1 in 5 quadrillion seconds even after traversing bumpy roads, a figure over ten times higher than that of portable atomic clocks operated in the United States.

The new atomic clock developed by the Institute of Measurement and Testing Technology operates similarly to a fountain. The clock cools cesium atoms using lasers and then shoots them vertically. During the process of the atoms falling back down due to gravity, they emit light. Counting the flashes provides accurate time information.

◇China competes with the U.S. for precision clocks

Atomic clocks are not only very complex and expensive but also require thorough maintenance. They are highly vulnerable to external factors such as vibrations and magnetic fields. In addition to atomic clocks, laser and microwave clocks also provide precise time information. However, these technologies require a lot of energy and can malfunction with even slight mishandling. Researchers stated that "the new atomic clock requires minimal maintenance and oversight and operates autonomously over long periods," calling it "ideal for military applications."

Researchers redesigned the ion pump of the clock and moved it to a central position, among other efforts. This ultimately contributed to drastically reducing the volume of the atomic clock. They revived a computer language that is now rarely used to enhance the overall efficiency and stability of the system. The program running the atomic clock was rewritten in assembly language, a programming language used by developers in the 1980s and 1990s.

Researchers from the China Academy of Metrology and the Research Institute of Measurement Science, as well as the Advanced Tracking Technology Innovation Center, revealed on the 18th (local time) that they have developed a small cesium atomic clock (NIM-TF3) the size of a 1.5m mini-refrigerator. The NIM-TF3 is small and sturdy enough not to waste time even if loaded onto a truck. /National Institute of Metrology

China is engaged in fierce competition with the United States to secure precise time information. The most accurate atomic clock on Earth still belongs to the United States, but a team led by Chinese researchers has created one. The Hong Kong South China Morning Post reported that as relations between the two countries have soured, some of these scientists are considering returning to China.

China is rapidly narrowing the technological gap by successively introducing innovative atomic clocks like the NIM-TF3. There are analyses suggesting that the atomic clocks used in China's Beidou satellites, which are referred to as the Chinese version of GPS, outperform those used in American GPS satellites. The hydrogen atomic clock mounted on China's Tiangong-2 space station broke the world record for time maintenance accuracy in space. Last year, China also started operating the world's longest and most accurate time synchronization optical fiber network.

In the scientific community, there are forecasts that under this trend, China could catch up to the United States within a few years. This suggests that the People's Liberation Army (PLA) could surpass the United States in electronic warfare, laser weaponry, and unmanned technologies.

◇Core of electronic warfare and cyber warfare

A strontium atomic clock in a laboratory at the University of Colorado Boulder. /NIST

High-precision time-maintenance systems, including atomic clocks, have emerged as the core of modern warfare. Accurate time information is essential for effectively operating radars that detect stealth fighters thousands of kilometers away. Precise time information is also needed to harness lasers or microwaves as powerful energy weapons to destroy enemies.

Encrypted secure communication systems rely on highly synchronized time. Precise time information is also necessary for calculating trajectories and coordinating attacks to enhance the accuracy of sophisticated weapon systems such as guided missiles. In operations like cyber warfare, where every millisecond (ms) counts, accurate time is crucial.

The United States is responding with a ‘nuclear clock’ that surpasses atomic clocks. The National Institute of Standards and Technology (NIST) and the University of Colorado Boulder are developing a ‘nuclear clock’ that will exhibit no more than a second of error over billions of years, using the rare isotope thorium-229. Unlike atomic clocks that depend on electronic transitions, nuclear clocks utilize frequencies based on the transitions of atomic nuclei, which are less influenced by external forces.

In September, researchers announced in the international journal Nature their discovery of the first high-resolution spectrum of nuclear transitions and reported the development of a nuclear clock device using thorium-229 crystals in collaboration with a research team from Vienna, Austria. They secured a method to reduce radioactivity to one-thousandth using thorium tetrafluoride (ThF4) thin films, significantly lowering costs as well. Scientists expect that within 2 to 3 years, nuclear clocks will surpass atomic clocks in accuracy.

Separately, the U.S. Department of Defense is advancing a project to develop improved atomic clocks for national key infrastructure, including defense, banking, and power systems. The Defense Advanced Research Projects Agency (DARPA) is developing a chip-scale atomic clock (CSAC) that is the size of a small chip but has performance increased by a factor of 1,000.

◇Nuclear clocks and quantum clocks are also in development

The Ministry of National Defense of the United Kingdom announced that it is developing a quantum clock that does not deviate by a second for billions of years through experimental quantum technology. /Ministry of National Defense

Movements to secure precise time systems in the defense sector are expanding. On the 2nd, the UK Ministry of Defense unexpectedly announced that it is developing a quantum clock to enhance the information and reconnaissance capabilities of the British military. The clock, which has been under wraps, is being developed by the Defense Science and Technology Laboratory (DSTL) and is precise enough to ensure no more than one second of error over billions of years through experimental quantum technology. The first experiments have been completed, incorporating feedback from the British Army and Navy.

The UK Ministry of Defense stated that it expects the quantum clock to reduce reliance on GPS, which can be disrupted or blocked by hostile countries, protect communication networks, and enhance the accuracy of advanced weaponry, adding that it plans to deploy it in military operations within the next five years. DSTL assessed that "the quantum clock is a significant achievement for the UK's quantum technology and will enhance navigation and operational capabilities while promoting advancements in industry and science, creating highly skilled jobs."

The Australian Department of Defense and QuantX Labs, based in Adelaide, announced that they have developed a quantum clock with an error of 30 billionths of a second. Quantum technology is one of the eight key technologies shared by the trilateral security partnership AUKUS, which includes the U.S., UK, and Australia. The Australian military has already acquired quantum optical atomic clocks to support its communication and navigation systems and plans to introduce additional atomic clocks for testing in mobile environments within this year. The Australian military aims to ensure normal operations of various weapon systems even in situations where GPS signals are jammed, utilizing quantum clocks.

Reference materials

Acta Metrologica Sinica (2024), http://jlxb.china-csm.org:81/Jwk_jlxb/EN/10.3969/j.issn.1000-1158.2024.12.19

Nature (2024), DOI: https://doi.org/10.1038/s41586-024-07839-6