I. Quantum Mechanical Basis of Atomic Energy Level Transitions

Energy Level Transition Mechanism

When electrons inside an atom transition between different energy states (the ground state and excited states), they will absorb or emit electromagnetic 

waves of specific frequencies. Such transition frequencies are determined by the laws of quantum mechanics and possess extremely high stability. For 

example, the cesium atomic clock uses the transition frequency (9,192,631,770 Hz) between two hyperfine energy levels of the cesium-133 atom as a 

reference.

Resonance Detection Principle

By adjusting the frequency of the external electromagnetic field (such as microwaves or lasers) to match the inherent transition frequency of the atom. 

When resonance is achieved, the atom will absorb a large amount of energy and undergo an energy level transition. At this time, the detection system 

locks onto this frequency as a time reference.

II. Implementation Paths of Key Technologies

Differences between Microwave Clocks and Optical Clocks

Microwave Clocks (such as cesium atomic clocks) use the microwave band (about 9 GHz) to stimulate atomic transitions, with an accuracy reaching an 

error of 1 second in every 20 million years.

Optical Clocks (such as strontium optical lattice clocks) utilize optical frequencies (about 429 THz), improving the accuracy to an error of 1 second in 30 

billion years. They convert high-frequency optical signals into countable low-frequency signals through optical frequency comb technology.

Feedback Control System

Atomic clocks contain a closed-loop adjustment system: the oscillator generates the initial frequency → the atomic resonance cavity detects the 

absorption peak → the feedback circuit corrects the oscillator frequency → finally, a stable signal is output. For example, the NIST-F2 cesium fountain

 clock achieves a stability on the order of E-16 through microwave resonance technology.

III. Scientific Breakthroughs in Performance Improvement

Material Selection

Cesium (Cs) and rubidium (Rb) have become the top choices due to their clear energy level structures and stable transition frequencies. In 2025, 

China's new rubidium clock has improved the second-level stability to E-14 (one part in a quadrillion), and the strontium optical lattice clock can even 

achieve an error of 1 second in billions of years.

Technological Evolution

From the first atomic clock in 1948 to the space cold atomic clock carried by Tiangong-2 in 2016, and then to the quantum clock developed by the UK 

in 2025, the technological path has developed from macroscopic devices to chip-level integration.

IV. Application Scenarios and Strategic Significance

The high precision of atomic clocks makes them the core components of satellite navigation systems (such as GPS and Beidou), enabling positioning 

through time ranging. In addition, fields such as deep space exploration, synchronization of financial transactions, and synchronization of 5G networks 

all rely on the nanosecond-level time reference provided by atomic clocks.