Share how CPT atomic clocks work and their key technologies

CPT atomic clock, the full name of coherent population trapping atomic clock, is a major innovation in the field of modern science and technology. Based on the basic principles of atomic physics, it shows great potential and application prospects in the fields of precision timing, scientific research and navigation and positioning. This article will elaborate on how CPT atomic clocks work and their key technologies.

1.Basic overview of CPT atomic clocks
CPT is an atomic clock that works on the principle of coherent cloth and imprisonment, and excites a specific kind of atom through laser to put it in a special quantum state. Unlike traditional cesium atomic clocks, CPT atomic clocks eliminate the need for microwave resonant cavities, achieving miniaturization and low power consumption. This feature allows CPT atomic clocks to be integrated into a single chip, so they are also known as "chip-scale atomic clocks" or CSAC(Chip Scale Atomic Clocks).

2.How it works
The core of the working principle of CPT atomic clocks lies in the Zeeman effect of the resonant absorption spectral line. When atoms are placed under magneto-optical resonance conditions, the atoms are excited by lasers to make the atoms transition from the ground state to the excited state. When there is a resonance between the excited state energy level and other energy levels, the atom will absorb the energy of the laser and produce an absorption peak. By accurately measuring the frequency of the absorption peak, a very precise time reference can be obtained.

Specifically, the working process of CPT atomic clocks is as follows:

(1)Laser Source Preparation: First, a highly stable laser is needed to provide a specific frequency of light to excite atoms.

(2)Atomic sample preparation: rubidium or other alkali metal atoms are usually used as the working medium, which are placed in a specially designed miniature cavity, such as glass bubbles or MEMS bubbles.

(3)Magnetic field modulation: A weak magnetic field is applied around the atomic sample, which changes periodically over time, causing the Zeeman splitting of the atomic energy level.

(4)Laser scanning: The light frequency emitted by the laser is scanned to cover multiple absorption peaks due to the Zeeman effect.

(5)Signal detection: When the laser frequency matches a certain ultra-fine energy level difference of the atom, resonant absorption will occur, forming an absorption peak. The position and intensity of the absorption peak are detected by a photodetector.

(6)Frequency Locking: Finally, a feedback control system is used to lock the laser frequency at the center of the absorption peak, resulting in a stable frequency output.

3.Key technologies

The performance of CPT atomic clocks is highly dependent on the following key technologies:
(1)Optical system: Includes high-stability light source, high-precision optical components, and optical tuning technology. The stability of these components directly impacts the accuracy and precision of the clock.
(2)Atomic cavities: The design and preparation of atomic cavities need to account for the interaction of atoms with the light field to achieve efficient atomic excitation and enhanced laser absorption peaks.

(3)Magnetic Field Control: Precise magnetic field control technology is key to ensuring the stability and accuracy of the bell. By finely adjusting the magnitude and direction of the magnetic field, optimal resonance conditions can be achieved.

(4)Frequency Counting and Control: The frequency of the absorption peak needs to be accurately measured and compared and corrected with the reference frequency. The design and optimization of frequency counters and feedback control systems are crucial for enhancing the accuracy and stability of the clock.

4.Application prospects
With its high precision, low power consumption, and miniaturization, CPT atomic clocks have shown broad application prospects in many fields:

(1)Scientific research: It has become an important tool for precision physics experiments, fundamental physics research and particle accelerator experiments, and can be used to verify physical laws, measure fundamental constants, and study quantum mechanics.

(2)Navigation and positioning: CPT atomic clocks with ultra-high time stability can provide high-precision time references and are used in areas such as GNSS, wireless communication network synchronization, and seismic monitoring.

(3)Time-Frequency Standards: High accuracy and stability make them strong candidates for time-frequency standards, which can be used for the measurement and transmission of national standard time, as well as in areas requiring high-precision time reference, such as financial transactions and power system synchronization.

(4)Inertial navigation and gravitational measurement: Provide high-precision time reference in inertial navigation systems to achieve precise positioning of aerospace vehicles; It is also used in the fields of gravitational measurement and gravitational wave detection.
CPT atomic clocks represent the latest development direction of atomic clock technology, and will play an increasingly important role in scientific research, navigation and positioning, time-frequency standards, and inertial navigation. With the continuous improvement of key technologies and the improvement of performance, the application prospects of CPT atomic clocks will be broader.