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arXiv:2608.06169

Dual-Faraday-laser-pumped cesium beam clock with $7.7\times 10^{-13}/\sqrtτ$ frequency stability

Xiaomin Qin, Suyang Wei, Haijun Chen, Yufei Yan, Qiang Wei, Hangbo Shi, Zhiyang Wang, Zheng Xiao, Zijie Liu, Tiantian Shi, Jingbiao Chen

physics.atom-phquant-phSubmitted Aug 6, 2026• Announced Aug 7, 2026
arXivHTMLPDF

Abstract

Compact cesium beam clocks are major frequency references for deployable timing systems. However, further improvement of their short-term frequency stability is limited by the clock signal-to-noise ratio (SNR). Although two-laser optical pumping can increase the effective atomic utilization, the achievable clock SNR has long been limited by laser-induced frequency-to-amplitude noise conversion. Here, we demonstrate a compact dual-Faraday-laser-pumped (DFP) Cs beam clock enabled by a low-frequency-noise atom-referenced laser architecture. The intracavity Faraday anomalous dispersion optical filter provides inherent alignment to the Cs D$_2$ resonances, while modulation transfer spectroscopy offers suppressed frequency noise and drift. The resulting laser system supports robust turnkey operation with a Lorentzian linewidth of 2.12 kHz. The DFP Cs clock achieves a clock SNR of 46,365 in a 1-Hz bandwidth and a fractional Allan deviation of $7.7\times 10^{-13}/\sqrtτ$ , with Hadamard deviation reaching $7.7\times 10^{-15}$ at 10,000 s. This work pushes the fractional frequency stability of a compact Cs beam clock into the $10^{-13}/\sqrtτ$ regime, providing a pathway toward high-performance Cs frequency references for field-deployable precision timing, navigation, and synchronization.

Comments
12 pages, 5 figures

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Dual-Faraday-laser-pumped cesium beam clock with 7.7×10−13/τ7.7\times 10^{-13}/\sqrtτ7.7×10−13/τ​ frequency stability
Compact cesium beam clocks are major frequency references for deployable timing systems. However, further improvement of their short-term frequency stability is limited by the clock signal-to-noise ratio (SNR). Although two-laser optical pumping can increase the effective atomic utilization, the achievable clock SNR has long been limited by laser-induced frequency-to-amplitude noise conversion. Here, we demonstrate a compact dual-Faraday-laser-pumped (DFP) Cs beam clock enabled by a low-frequency-noise atom-referenced laser architecture. The intracavity Faraday anomalous dispersion optical filter provides inherent alignment to the Cs D2_22​ resonances, while modulation transfer spectroscopy offers suppressed frequency noise and drift. The resulting laser system supports robust turnkey operation with a Lorentzian linewidth of 2.12 kHz. The DFP Cs clock achieves a clock SNR of 46,365 in a 1-Hz bandwidth and a fractional Allan deviation of 7.7×10−13/τ7.7\times 10^{-13}/\sqrtτ7.7×10−13/τ​ , with Hadamard deviation reaching 7.7×10−157.7\times 10^{-15}7.7×10−15 at 10,000 s. This work pushes the fractional frequency stability of a compact Cs beam clock into the 10−13/τ10^{-13}/\sqrtτ10−13/τ​ regime, providing a pathway toward high-performance Cs frequency references for field-deployable precision timing, navigation, and synchronization.
Distributed Bragg reflector (DBR) lasers have found promising prospects in quantum sensing, cold atom physics, and precision spectroscopy. However, a broader implementation is challenged by their MHz-scale linewidths and the absence of autonomous atomic resonance alignment. Here, we demonstrate a turnkey 795 nm DBR laser system locked to the Rb 85 D 1 hyperfine transition. Our approach employs a dual-stage architecture: stage 1 utilizes the Faraday anomalous dispersion optical filter (FADOF) with optical feedback, achieving automatic frequency resonance and confinement to the vicinity of the Rb 85 D 1 line, while reducing the 1/ π integral linewidth from 461.8 kHz to 28.8 kHz, and the Lorentzian linewidth from 25.8 kHz to 426.9 Hz. This mechanism is quantitatively investigated using Lang–Kobayashi equations. Stage 2 applies modulation transfer spectroscopy (MTS) to further stabilize the frequency of the optically locked laser, which yields an Allan deviation of 3.29×10 −13 / τ . Our system unlocks DBR lasers’ potential in quantum precision measurements, offering a convenient, compact, low-noise light source for atomic clocks, magnetometers, and gyroscopes.
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Optical clocks with high precision are practical and necessary in atomic physics, geodesy, gravitational wave measurement, etc. Transportability and environmental adaptability are two key indicators to measure the performance of frequency standards. Here, we utilized a highly robust atomic-filter-based Faraday laser as the local oscillator, and achieved two compact Faraday optical frequency standards based on 133Cs6S1/2|F=3⟩→6P3/2|F′=2⟩ and 6S1/2|F=4⟩→6P3/2|F′=5⟩ transitions at 852 nm, leveraging modulation transfer spectroscopy for laser frequency stabilization. The Faraday laser automatically aligns atomic transition spectral lines, due to the use of atomic filters as frequency selective elements. Therefore, the laser wavelength has strong robustness against environmental changes. This setup not only simplifies the operational complexity but also ensures frequency stability. By heterodyne beating between two such compact optical frequency standards, the beatnote achieved a short-term frequency stability of 1.68 × 10−13 at 3 s, remained at the 10−13 level for up to 400 s, and stayed below 2.7 × 10−12 for up to 1600 s, predominantly exhibiting white frequency noise. This underscores the potential of atomic-filter-based Faraday laser in realizing compact and stable frequency standards, mitigating coherent communication error rates, and enhancing the precision of quantum interferometric measurements. Moreover, this approach eliminates the continuous need for external monitoring and adjustments, thereby, offering a practical and robust solution for out of laboratory applications demanding high frequency stability.
The Faraday laser, with Faraday anomalous dispersion optical filter (FADOF) as frequency-selection element, is a natural narrow-bandwidth light source for laser physic experiments. In this work, a dual-frequency (DF) Faraday laser is demonstrated for the first time on Cs D2 line at 852 nm. The frequencies of the two modes of DF Faraday laser hinge on the peak transition frequencies of 852 nm FADOF transmittance spectrum corresponding to the ground state F=4 and F=3. The frequency difference between the two modes is tunable over a range of 1.4 GHz with the temperature of Cs vapor cell inside the FADOF. The linewidth of each laser mode is less than 33 kHz. Furthermore, the most probable linewidth of the beat-note spectra between the two modes is 902.95 Hz at different vapor-cell temperatures. Such a DF Faraday laser has many potential applications in atomic physics, such as sub-Doppler spectroscopy and coherent population trapping atomic clocks.