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arXiv · 2507.19449

A continuous-wave vacuum ultraviolet laser for the nuclear clock

Qi Xiao·Gleb Penyazkov·Xiangliang Li·Beichen Huang·Wenhao Bu·Juanlang Shi·Haoyu Shi·Tangyin Liao·Gaowei Yan·Haochen Tian·Yixuan Li·Jiatong Li·Bingkun Lu·Li You·Yige Lin·Yuxiang Mo·Shiqian Ding
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Abstract

The exceptionally low-energy isomeric transition in $^{229}$Th at around 148.4 nm offers a unique opportunity for coherent nuclear control and the realisation of a nuclear clock. Recent advances, most notably the incorporation of large ensembles of $^{229}$Th nuclei in transparent crystals and the development of pulsed vacuum-ultraviolet (VUV) lasers, have enabled initial laser spectroscopy of this transition. However, the lack of an intense, narrow-linewidth VUV laser has precluded coherent nuclear manipulation. Here we introduce and demonstrate the first continuous-wave laser at 148.4 nm, generated via four-wave mixing (FWM) in cadmium vapor. The source delivers 100 nW of power with a linewidth well below 100 Hz and supports broad wavelength tunability. This represents a five-orders-of-magnitude improvement in linewidth over all previous single-frequency lasers below 190 nm, marking a major advance in laser technology. We develop a spatially resolved homodyne technique to place a stringent upper bound on the phase noise induced by the FWM process and demonstrate sub-hertz linewidth capability. These results eliminate the final technical hurdle to a $^{229}$Th-based nuclear clock, opening new directions in quantum metrology, nuclear quantum optics and precision tests of the Standard Model. More broadly, they establish a widely tunable, ultranarrow-linewidth laser platform for applications across quantum information science, condensed matter physics, and high-resolution VUV spectroscopy.

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Qi Xiao, Gleb Penyazkov, Xiangliang Li, Beichen Huang, Wenhao Bu, Juanlang Shi, Haoyu Shi, Tangyin Liao, Gaowei Yan, Haochen Tian, Yixuan Li, Jiatong Li, Bingkun Lu, Li You, Yige Lin, Yuxiang Mo, Shiqian Ding. 2025-07-25. A continuous-wave vacuum ultraviolet laser for the nuclear clock. https://doi.org/10.1038/s41586-026-10107-4

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