1 National Time Service Center, Chinese Academy of Sciences, Xi'an 710600, China; 2 Key Laboratory of Time Reference and Applications, Chinese Academy of Sciences, Xi'an 710600, China; 3 State Key Laboratory of Photonics and Communications, Institute of Quantum Electronics, School of Electronics, Peking University, Beijing 100871, China; 4 University of Chinese Academy of Sciences, Beijing 100049, China; 5 School of Integrated Circuits, Peking University, Beijing 100871, China; 6 National Key Laboratory of Advanced Micro and Nano Manufacture Technology, Beijing 100871, China; 7 Hefei National Laboratory, Hefei 230088, China
Abstract The phenomenon that a clock at a higher gravitational potential ticks faster than one at a lower potential, also known as gravitational redshift, is one of the classical tests of Einstein's theory of general relativity. Owing to their ultra-high accuracy and stability, state-of-the-art optical lattice clocks have enabled resolving the gravitational redshift with a millimeter-scale height difference. Further reducing the vertical inter-clock separation down to the sub-millimeter level and especially shortening the required measurement time may be achieved by employing spin squeezing. Here, we theoretically investigate the spin-squeezing-enhanced differential frequency comparison between two optical clocks within a lattice-trapped cloud of Yb atoms. The numerical results illustrate that for a sample of atoms, the atomic-collision-limited resolution of the vertical separation between two clocks can reach 0.48 mm, corresponding to a fractional gravitational redshift at the level. In addition, the required averaging time may be reduced to less than one hundredth of that of conventional clocks with independent atoms. Our work opens a door to the future spin-squeezing-enhanced test of general relativity.
Fund: in Basic Research (Grant No. YSBR-085), the National Time Service Center (Grant No. E239SC1101), Innovation Program for Quantum Science and Technology (Grant No. 2021ZD0303200), and China Postdoctoral Science Foundation (Grant No. BX2021020).
Corresponding Authors:
Tiantian Shi
E-mail: tts@pku.edu.cn
Cite this article:
Deshui Yu(于得水), Jia Zhang(张佳), Shougang Zhang(张首刚), Tiantian Shi(史田田), and Jingbiao Chen(陈景标) Resolving gravitational redshift with sub-millimeter height differences using spin-squeezed optical clocks 2025 Chin. Phys. B 34 054208
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