Direct Laser Cooling Al^＋ Ion Optical Clocks

• Published in: Chinese physics letters 2017-05, Vol.34 (5), p.31-35
• Main Author: 张洁 邓科 罗俊 陆泽晃
• Format: Article
• Language: English
• Subjects: 光学钟; 光稳定性; 多普勒冷却; 多普勒频移; 激光冷却; 量子逻辑; 铝离子; 黑体辐射
• ISSN: 0256-307X; 1741-3540
• DOI: 10.1088/0256-307X/34/5/050601

The Al^＋ ion optical clock is a very promising optical frequency standard candidate due to its extremely small black-body radiation shift. It has been successfully demonstrated with the indirect cooled, quantum-logic-based spectroscopy technique. Its accuracy is limited by second-order Doppler shift, and its stability is limited by the number of ions that can be probed in quantum logic processing. We propose a direct laser cooling scheme of AI＋ ion optical clocks where both the stability and accuracy of the clocks are greatly improved. In the proposed scheme, two Al^＋ traps are utilized. The first trap is used to trap a large number of Al^＋ ions to improve the stability of the clock laser, while the second trap is used to trap a single Al^＋ ion to provide the ultimate accuracy. Both traps are cooled with a continuous wave 167nm laser. The expected clock laser stability can reach 9.0 × 10^-17/√τ. For the second trap, in addition to 167nm laser Doppler cooling, a second stage pulsed 234nm two-photon cooling laser is utilized to further improve the accuracy of the clock laser. The total systematic uncertainty can be reduced to about 1 × 10^-18. The proposed Al^＋ ion optical clock has the potential to become the most accurate and stable optical clock.