Design of a fiber cavity ion trap for a high-efficiency and high-rate quantum network node
Authors: Bao Xing-Yu , Cui Jin-Ming , Fang Ding , Chen Wei-Bin , Wang Jian , Huang Yun-Feng , Li Chuan-Feng , Guo Guang-Can ,   CAS Key Laboratory of Quantum Information, University of Science and Technology of China, Hefei 230026, China,   CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, China,   Hefei National Laboratory, University of Science and Technology of China, Hefei 230088, China
Published: June 2023

The main purpose of this paper is to design a novel coupled system of an ion trap and a fiber cavity. This integrated solution is achieved by fabricating a fiber cavity with a metal mask on the side and end faces of the fiber. The fiber cavity with the metal mask can transmit light and electric charges, and the metal mask on the fiber end-face can shield electric charges on the dielectric high-reflection film. This system is designed to trap a single <inline-formula><tex-math id="M1">\begin{document}$ ^{138}\text{Ba}^{+} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="JUSTC-2023-0005_M1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="JUSTC-2023-0005_M1.png"/></alternatives></inline-formula> ion and realize coupling of the fiber cavity to the fluorescence at a 493 nm wavelength of <inline-formula><tex-math id="M2">\begin{document}$ ^{138}\text{Ba}^{+} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="JUSTC-2023-0005_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="JUSTC-2023-0005_M2.png"/></alternatives></inline-formula>. To efficiently collect fluorescent photons, we perform a theoretical analysis of the overall system to achieve optimal coupling of each individual part. The cavity length is designed to be <inline-formula><tex-math id="M3">\begin{document}$ 250 $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="JUSTC-2023-0005_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="JUSTC-2023-0005_M3.png"/></alternatives></inline-formula> μm, and the optimized coupling parameters are <inline-formula><tex-math id="M5">\begin{document}$(g,\kappa,\gamma)/2{\text{π}}=(55,\;105,\;20)$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="JUSTC-2023-0005_M5.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="JUSTC-2023-0005_M5.png"/></alternatives></inline-formula> MHz. We also improve the stability and reliability of the system by analyzing the vibration, performance of the ion trap, and thermal stability. The core of the system is composed of materials with similar thermal expansion coefficients to improve thermal stability. The system uses spring connections to isolate vibrations inside and outside the vacuum chamber. We theoretically solve the difficulties of manufacturing the coupled system and have completed the experimental verification of some key technologies. The whole system is expected to be extended into a complex quantum network system to realize quantum computation and communication.