Chinese Academy of Sciences Develops Compact Optical Clock with Breakthrough Stability
Recently, the atomic clock research team at the National Time Service Center (NTSC) of the Chinese Academy of Sciences (CAS) has successfully developed a compact optical clock based on quantum-interference-enhanced absorption spectroscopy. This innovation is expected to play a crucial role in micro-positioning, navigation, and timing (μPNT) systems, marking a significant leap forward in precision timekeeping technology.
In the advancement of modern technology, high-precision time measurement and frequency standards are indispensable. From global satellite navigation systems to high-speed communication networks and scientific experiments, ultra-accurate time and frequency references are fundamental. Optical clocks, as one of the most precise time-frequency standards, have become a focal point for researchers worldwide.
The NTSC team has long been dedicated to advancing atomic clock technology. Their previous success in developing a chip-scale microwave atomic clock based on coherent population trapping (CPT) laid a solid foundation for this research. Meanwhile, progress in optical frequency comb technology has opened new avenues for optical clock development.
Inspired by these achievements, the team proposed and demonstrated a chip-scale optical clock utilizing two-photon transitions in a rubidium atomic ensemble. Compared to conventional optical clocks, this design significantly improves frequency stability and accuracy. However, traditional approaches face critical limitations—such as requiring high vapor cell temperatures (100°C) and substantial laser power (10 mW)—which hinder miniaturization and energy efficiency.
For real-world applications like μPNT systems, compact size and low power consumption are non-negotiable. Thus, the demand for fully miniaturized, low-power optical clocks has become urgent.
To overcome these constraints, the researchers explored an innovative approach focusing on the rubidium D₁ line. Their breakthrough came from exploiting sub-Doppler enhanced absorption resonances in this transition.
By using monochromatic light and precisely adjusting the polarization of counter-propagating pump and probe beams, the team observed a unique phenomenon: constructive and destructive interference between two dark states prepared by the pump and probe lights. This interference led to absorption enhancement, producing Doppler-free resonance signals with a high signal-to-linewidth ratio—ideal for high-performance optical clocks.
Compared to traditional methods, this approach drastically reduces requirements:
✔ Laser power: Only ~100 µW (vs. 10 mW)
✔ Operating temperature: ~40°C (vs. 100°C)
The team also developed a theoretical model to explain the underlying physics, highlighting the critical role of Zeeman dark states. Experimental results aligned perfectly with simulations, validating the model and guiding further optimizations.
After prototyping the compact optical clock, the team rigorously tested its frequency stability. By locking two identical semiconductor lasers to the enhanced sub-Doppler resonance, they achieved remarkable results:
This represents a 100-fold improvement over free-running lasers, demonstrating the clock's exceptional precision and practicality.
With its outstanding performance, this compact optical clock holds vast potential across multiple fields:
🔹 Instrumentation: Serves as an ultra-precise frequency reference, enhancing measurement accuracy in research and industry.
🔹 Navigation: Improves positioning accuracy for satellite and indoor navigation systems.
🔹 Metrology: Advances precision in physical quantity measurements.
🔹 Communications & Finance: Supports secure, high-speed data transmission and timestamping.
As the technology matures, this innovation could become a cornerstone for next-generation timing systems, driving progress across science and industry.
Key Technical Terms
(Note: The translation preserves technical accuracy while adapting phrasing for international readability. Institutional names (e.g., 中国科学院) retain official English designations.)
