Time and frequency currently stand as the most precisely measurable physical parameters, with atomic optical clocks representing the pinnacle of accuracy. Yet, clocks based on the nuclear properties of thorium-229 (229Th) could potentially redefine these standards.
What sets 229Th apart is its remarkable suitability for laser-based manipulation of nuclear quantum states, a trait not found in other nuclides. This unique feature paves the way for a next-generation nuclear optical clock, promising a quantum leap in timekeeping precision. Because a nucleus is far smaller than an entire atom, it is intrinsically less affected by external environmental fluctuations. Moreover, the well-separated energy levels of nuclear quantum states, shielded by extranuclear electrons, further enhance its potential stability.
The pursuit of a nuclear clock using 229Th traces back nearly 50 years, originating with the identification of its unusually low-lying excited nuclear state. This landmark discovery laid the conceptual foundation for nuclear timekeeping. Breakthroughs continued to accumulate, culminating in 2024 with the first successful laser excitation of the 229Th nuclear transition. Experimental advances have since been achieved across global research institutions, including TU Wien, UCLA, and JILA, where scientists employed diverse platforms such as doped crystal matrices and ultra-thin films to probe the nuclear transition dynamics.
Despite this progress, formidable technical barriers persist. The behavior of nuclear transitions in solid-state systems can fluctuate significantly with temperature. Additional complications stem from the rarity of the 229Th isotope, the absence of a dedicated laser with both high power and narrow linewidth, and unresolved complexities in nuclear-electronic interaction mechanisms. The inability to implement closed-loop feedback systems also limits the clock's development.
Nevertheless, overcoming these challenges could herald a new era in chronometry. A fully operational thorium nuclear optical clock would not only surpass current atomic standards but also catalyze breakthroughs in fundamental physics. By shifting the operational principle from electronic to nuclear transitions, it could reveal deeper truths about the universe's underlying framework.
Research Report:The ticking of thorium nuclear optical clocks: a developmental perspective
Related Links
Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences
Understanding Time and Space
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