Laser excitation of the $^{229}$Th nuclear isomeric transition in a solid-state host

Abstract: LiSrAlF$6$ crystals doped with $^{229}$Th are used in a laser-based search for the nuclear isomeric transition. Two spectroscopic features near the nuclear transition energy are observed. The first is a broad excitation feature that produces red-shifted fluorescence that decays with a timescale of a few seconds. The second is a narrow, laser-linewidth-limited spectral feature at $148.38219(4){\textrm{stat}}(20){\textrm{sys}}$ nm ($2020407.3(5){\textrm{stat}}(30){\textrm{sys}}$ GHz) that decays with a lifetime of $568(13){\textrm{stat}}(20){\textrm{sys}}$ s. This feature is assigned to the excitation of the $^{229}$Th nuclear isomeric state, whose energy is found to be $8.355733(2){\textrm{stat}}(10)_{\textrm{sys}}$ eV in $^{229}$Th:\thor:LiSrAlF$_6$.

Laser Excitation of the 229Th Nuclear Isomeric Transition in a Solid-State Host: Insights and Implications

Overview

The paper presents a significant study on the laser excitation of the notable low-energy nuclear isomeric state in the 229Th nucleus, using LiSrAlF₆ crystals doped with 229Th. This research delves deeply into the spectroscopic features around the nuclear transition energy and provides critical observations that advance our understanding and application possibilities of this unique nuclear state.

Key Findings

The researchers identified two distinct spectroscopic features near the nuclear transition energy through laser-based experimentation:
- A broad excitation feature associated with fluorescence that decays over a few seconds.
- A sharp, laser-linewidth-limited spectral peak at 148.38219 nm (statistical uncertainty: 4 pm; systematic uncertainty: 20 pm), correlating to the excitation of the 229Th nuclear isomeric state. This particular feature decays with a lifetime measured as 568 seconds, offering valuable data about the stability of the excited nuclear state in the crystal matrix.

The exact energy of the nuclear isomeric state in 229Th:LiSrAlF₆ was determined to be approximately 8.355733 eV, which affirms earlier theoretical predictions and refines current measurements with laser spectroscopic precision.

Implications and Future Developments

The identification of the nuclear transition with high precision opens significant pathways for research and application:
- Optical Nuclear Clock: The 229Th nuclear isomeric transition is potentially key to developing optical nuclear clocks, which would outperform current standards, especially in terms of robustness and accuracy.
- Testing Fundamental Constants: The precision achieved in measuring the isomeric transition makes this system an excellent candidate for exacting tests of fundamental physical constants, aiding in potential discoveries of variances over time or under different physical conditions.
- Nuclear and Material Physics: The insights provided by observing the interactions between thorium nuclei and the host crystal's electronic structure could deepen our understanding of nuclear decay processes and their interference with host structures.

The paper not only lays a foundation for further theoretical inquiries about isomeric transitions in other solid-state environments but also encourages the exploration of differing lattice structures and impurity incorporations to optimize the sensitivity and selectivity of these phenomena.

Conclusion

This research offers a meticulous examination of the 229Th isomeric state, achieving remarkable spectral precision and confirming theoretical predictions with empirical data. As such, it can lead to extensive advancements in clock technology, fundamental physics testing, and offers a path to expand our comprehension of nuclear behaviors within solid-state systems. The applications and scientific inquiries informed by this work have the potential to not only redefine aspects of timekeeping but also extend into broader domains of quantum and materials science.