Direct detection of the 229Th nuclear clock transition (1710.11398v1)

Abstract: Today's most precise time and frequency measurements are performed with optical atomic clocks. However, it has been proposed that they could potentially be outperformed by a nuclear clock, which employs a nuclear transition instead of the atomic shell transitions used so far. By today there is only one nuclear state known which could serve for a nuclear clock using currently available technology, which is the isomeric first excited state in $^{229}$Th. Here we report the direct detection of this nuclear state, which is a further confirmation of the isomer's existence and lays the foundation for precise studies of the isomer's decay parameters. Based on this direct detection the isomeric energy is constrained to lie between 6.3 and 18.3 eV, and the half-life is found to be longer than 60 s for $^{229\mathrm{m}}$Th$^{2+}$. More precise determinations appear in reach and will pave the way for the development of a nuclear frequency standard.

• The paper reports the first direct detection of the 229Th nuclear isomeric state, finding an energy range of 6.3–18.3 eV and a half-life exceeding 60 seconds.
• The experimental setup combined a radio-frequency funnel, quadrupole mass separator, and micro-channel plate detector to overcome limits of previous indirect methods.
• The results pave the way for nuclear clock development, promising enhanced precision in timekeeping and impactful advances in fundamental physics research.

Direct Detection of the $^{229}$Th Nuclear Clock Transition

The paper presents a significant advancement in the paper of the isomeric state of thorium-229 ($^{229}$Th), specifically focusing on its potential use for developing nuclear-based frequency standards. Unlike traditional atomic clocks that employ atomic shell transitions, a nuclear clock based on $^{229}$Th utilizes nuclear transitions, which theoretically could deliver superior performance in terms of precision and stability. This work reports the first direct detection of the $^{229}$Th isomeric state, a crucial step towards achieving a functioning nuclear clock.

Key results from the paper include the characterization of the isomeric energy level and half-life. The isomeric energy was precisely constrained between 6.3 and 18.3 eV. This range is consistent with prior theoretical predictions and aligns with the need for optical excitability, which would allow laser-based manipulation akin to processes used in atomic physics. The experiments also determined a half-life greater than 60 seconds for $^{229\mathrm{m}$Th in the 2+ charge state, which indicates the possibility of storing these states for practical applications.

The rigorous experimental setup employed in this paper is noteworthy. The researchers utilized a nuanced combination of a radio-frequency and direct-current funnel system, mass separation through a quadrupole mass-separator, and a micro-channel plate detector to achieve the direct detection of the $^{229}$Th isomer. The detection mechanism involves collecting thorium ions on the detector's surface and observing the ensuing decay signals, which are attributed to the isomeric state's internal conversion (IC) electron emissions. This approach overcomes the limitations of previous indirect observation methods and provides a robust framework for further investigations.

Several implications arise from this research, both practical and theoretical. A nuclear clock based on $^{229}$Th could substantially outperform current atomic clocks in terms of resistance to environmental perturbations and compactness, offering potential breakthroughs in precision measurement technologies. Such advancements could significantly impact fields ranging from global positioning systems to fundamental physics investigations, including exploring variations in fundamental constants over time.

The direct detection of the $^{229}$Th isomer opens new pathways for research. Future work could focus on refining the measurement of the isomeric state's parameters and exploring different mechanisms for population and de-excitation, such as electronic bridge processes or direct laser excitation. Using cryogenic traps and high-resolution electron spectroscopy could provide deeper insights into the decay mechanisms and allow precise determination of the nuclear transition energy, facilitating the direct optical control of nuclear states.

In conclusion, the direct detection of the $^{229}$Th nuclear clock transition represents a pivotal step forward. By bridging the domains of nuclear and atomic physics, it lays the groundwork for developing a nuclear clock with wide-ranging applications, from enhancing the precision of time-keeping to probing the fundamentals of our physical universe. Continued efforts in this domain promise to unlock new dimensions of temporal measurement and nuclear state manipulation.