Speaker
Description
Precision spectroscopy of few-electron systems, such as hydrogen and helium, has significantly advanced modern physics. By comparing high-precision spectroscopy measurements in these simple atomic systems with theoretical calculations, we can test quantum electrodynamics (QED), determine fundamental physical constants, and impose constraints on physics beyond the Standard Model. Over the past decade, our group has performed precision spectroscopy measurements of the $2^3P$ fine structure and the $2^3S−2^3P$ transition in $^4\mathrm{He}$ [1,2]. Subsequently, we upgraded our beam apparatus by incorporating a zeeman slower, enabling the production of a metastable helium beam with tunable velocities [3]. Additionally, we enhanced the detection scheme by switching between counter-propagating traveling waves, rather than using a standing wave for spectroscopy [4]. These advancements enabled us to uncover the influence of the postselection effect on precision spectroscopy [5]. This effect can introduce deviations exceeding 20 times the statistical uncertainty, and we validated this finding through both theory and simulations [6]. Combining our results with the existing $^3\mathrm{He}$ result, we obtained an isotope shift of 1.0733(21) $\mathrm{fm}^2$. Unfortunately, the postselection effect also impacted the $^3\mathrm{He}$ measurement, prompting us to refine the detection method accordingly. Validation of this detection scheme and further spectroscopy of $^3\mathrm{He}$ are currently underway.
[1] X. Zheng, Y. R. Sun, J. -J. Chen, W. Jiang, K. Pachucki and S. -M. Hu, Phys. Rev. Lett. 118, 063001 (2017).
[2] X. Zheng, Y. R. Sun, J. -J. Chen, W. Jiang, K. Pachucki and S. -M. Hu, Phys. Rev. Lett. 119, 263002 (2017).
[3] J. -J. Chen, Y. R. Sun, J. -L. Wen and S. -M. Hu, Phys. Rev. A 101, 053824 (2020).
[4] J. -L. Wen, J. -D. Tang, J. -F. Dong, X. -J. Du, S. -M. Hu and Y. R. Sun, Phys. Rev. A 107, 042811 (2023).
[5] J. -L. Wen, J. -D. Tang, Y. -N. Lv, Y. R. Sun, C. -L. Zou, J. -F. Dong, and S. -M. Hu, Sci. Adv. 11, eadu9796 (2025).
[6] J. -D. Tang, J. -L. Wen, J. -F. Dong, Y. R. Sun, Y. -N. Lv and S. -M. Hu, Phys. Rev. A 112, 052814 (2025).