Magnetic-Field-Calibration-Free Determination of the Hyperfine Constant A in Ultracold Fermi gases of ⁴⁰K

@misc{yang2026magneticfieldcalibrationfree,
  title = {{Magnetic-Field-Calibration-Free Determination of the Hyperfine Constant $A$ in Ultracold Fermi gases of $^40$K}},
  author = {Yajing Yang and Biao Shan and Yuhang Zhao and Jiahui Shen and Zhuxiong Ye and Liangchao Chen and Zengming Meng and Pengjun Wang and Wei Han and Jing Zhang and Lianghui Huang},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.02572},
  eprint = {2609.02572},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.02572},
}

TY  - UNPB
TI  - Magnetic-Field-Calibration-Free Determination of the Hyperfine Constant A in Ultracold Fermi gases of ^40K
AU  - Yajing Yang
AU  - Biao Shan
AU  - Yuhang Zhao
AU  - Jiahui Shen
AU  - Zhuxiong Ye
AU  - Liangchao Chen
AU  - Zengming Meng
AU  - Pengjun Wang
AU  - Wei Han
AU  - Jing Zhang
AU  - Lianghui Huang
PY  - 2026
DA  - 2026/09/02
PB  - arXiv
DO  - 10.48550/arxiv.2609.02572
UR  - https://arxiv.org/abs/2609.02572
AB  - Hyperfine constant A is a key parameter of the hyperfine structure and underpins precision spectroscopy and metrology. In this Letter, we develop a magnetic-field-calibration-free method for determining the ground-state hyperfine constant A in an ultracold ^40K Fermi gas by utilizing a pair of magnetically insensitive ("clock") transitions. This overcomes the stringent magnetic-field calibration requirements of conventional methods. We measure the transition frequency between these two magnetically insensitive transitions with Hz-level resolution over a range of magnetic fields, and obtain the ground-state hyperfine constant A = −h× 285.730536(2) MHz, corresponding to an absolute uncertainty of about 2 Hz. Our value reduces the uncertainty by nearly three orders of magnitude compared with previous determinations, providing a substantially improved reference for high-precision spectroscopy and metrology with ^40K.
ER  -