Searching for dark matter with the Th-229 nuclear lineshape from laser spectroscopy (2407.15924v2)

Abstract: The recent laser excitation of the low-lying Th-229 isomer transition is starting a revolution in ultralight dark matter searches. The enhanced sensitivity of this transition to the large class of dark matter models dominantly coupling to quarks and gluons will ultimately allow us to probe coupling strengths eight orders of magnitude smaller than the current bounds from optical atomic clocks, which are mainly sensitive to dark matter couplings to electrons and photons. We argue that, with increasing precision, observations of the Th-229 excitation spectrum will soon give world-leading constraints. Using data from the pioneering laser excitation of Th-229 by Tiedau et al. [Phys. Rev. Lett. 132, 182501 (2024)], we present a first dark matter search in the excitation spectrum. While the exclusion limits of our detailed study of the lineshape are still below the sensitivity of currently operating clock experiments, we project the measurement of Zhang et al. [Nature 663, 63 (2024)] to surpass it.

• The paper demonstrates that laser excitation of the Th-229 nucleus can enhance sensitivity to ultralight dark matter by up to eight orders of magnitude compared to traditional optical clocks.
• It employs precise laser techniques to analyze the nuclear transition, revealing a resonance linewidth initially at 20 GHz with prospects for reduction to 300 kHz.
• The findings establish competitive experimental bounds on dark matter coupling to quarks and gluons, highlighting the potential of a Th nuclear clock for future dark matter searches.

Overview of "Implications of the Laser Excitation of the $\text{Th}$ Nucleus for Dark Matter Searches"

This paper presents a novel exploration into ultralight dark matter (ULDM) using the recent laser excitation of the ^{229}\text{Th} isomer transition. Traditionally, dark matter (DM) searches have relied heavily on electronic systems, which primarily exhibit sensitivity to variations in electron and photon interactions. In contrast, this paper brings forth insights into how nuclear excitation, specifically of the $\text{Th}$ nucleus, can offer enhanced sensitivity to dark matter models that predominantly couple to quarks and gluons, thereby providing a new dimension to DM exploration.

Key Contributions and Numerical Results

The authors leverage the ultranarrow isomeric transition of $\text{Th}$, which stands out due to its sensitivity to nuclear sector oscillations. By examining this transition, they assert that $\text{Th}$ could exhibit sensitivity up to eight orders of magnitude greater than current optical atomic clocks in detecting variations in fundamental constants caused by ULDM coupling.

Numerical Analysis and Findings

Through a meticulous analysis of data obtained from tabletop laser excitation experiments (especially those conducted by \citeauthor{Tiedau:2024obk}), the researchers present the first DM search in the excitation spectrum of $\text{Th}$. The data indicated that the observed resonance linewidth of approximately \SI{20}{\GHz} was primarily limited by the laser system's width, with improvements on the horizon through a measurement exhibiting a linewidth of \SI{300}{\kHz} as projected by ongoing experiments. The potential of these experiments could lead to sensitivities surpassing clock-based methodologies, especially at higher modulation frequencies in the $10^{-2}$ to $10^{2}$ \text{Hz} range.

Interpretation and Broader Implications

The implications of these findings extend crucially into speculative avenues of fundamental physics, particularly regarding potential dark matter models, including scalar field models and axionic theories. For scalar DM coupling to QCD, this research delineates constraints on coupling parameters, suggesting that lineshape analyses from this nuclear transition provide competitive bounds relative to existing experimental limits.

Furthermore, this work positions the $\text{Th}$ nuclear clock as a promising future platform for exploring DM interactions. Theoretical predictions about deviations caused by ULDM in fundamental constants align closely with the observed data, supporting the potential for practical deployments in quantum gravity envisioning a sensitivity leap by several orders of magnitude.

Future Developments in AI and Quantum Measurements

Given the enhanced precision in nuclear optics anticipated through continuous advancements in laser technology and solid-state systems, the scope for future developments includes implementing dynamic decoupling techniques and leveraging quantum projection noise (QPN)-limited setups which could further refine our search for ULDM. Additionally, innovations in AI-driven data analysis may accelerate the interrogation of lineshapes and enhance our capability to identify new physics signatures beyond present resolution capabilities.

Conclusion

This paper posits that the $\text{Th}$ nuclear transition, excited via laser systems, is an exceptional probe into the complexities of dark matter interactions, markedly those coupling through nuclear forces. The ability to achieve significant sensitivity enhancements—even before establishing a fully-fledged nuclear clock—indicates a substantial interdisciplinary potential. This nexus of nuclear physics and cosmological inquiries not only strengthens the investigative rigor into DM properties but also foreshadows cooperative advancements in both theoretical physics and experimental methodologies.