The era of nuclear timekeeping approaches.
For the first time, researchers utilize a compact laser to elevate an atomic nucleus. This accomplishment propels scientists closer to developing the inaugural nuclear clock, relying on atomic nuclei for timekeeping precision.
This progress represents an "extraordinary advancement," remarks Olga Kocharovskaya, a Texas A&M University physicist, unaffiliated with the study.
In comparison to atomic timepieces — presently scientists' most exact chronometers — nuclear clocks might offer simplicity and increased portability. Moreover, they could facilitate novel assessments of fundamental physics principles. With this recent development, the realization of a nuclear clock appears more feasible than ever: “We now comprehend its conceptual viability,” remarks physicist Peter Thirolf from Ludwig-Maximilians-Universität München in Germany, who wasn't involved in the study.
Established atomic clocks rely on the behavior of the electrons enveloping atoms. Within these atoms, electrons occupy distinct energy tiers. Inducing an electron to transition to a higher energy level necessitates precisely calibrated laser energy. This energy aligns with a specific light frequency emitted by the laser. Scientists direct a laser at an atom cluster and adjust its frequency until the electrons transition (SN: 10/5/17). This frequency serves as a temporal benchmark, akin to an atomic pendulum, governing time.
Nuclear clocks would utilize atomic nuclei transitions instead of electrons to define time intervals. Though most atomic nuclei possess energy gaps too wide for laser-triggered transitions, an exceptional nucleus stands apart. Thorium-229, a thorium variant, exhibits an exceptionally minute energy transition, within laser accessibility.
Up until recently, the magnitude of this leap remained uncertain. Nonetheless, in 2023, researchers refined its measurement to unprecedented accuracy (SN: 6/1/23).
This breakthrough paved the way for the subsequent phase. Employing a laser, scientists elevated thorium-229 nuclei to a heightened energy state, observing the resultant emitted light upon their descent. The study precisely determined the energy of this transition: 8.35574 electron volts, as detailed in a forthcoming paper in Physical Review Letters. While aligning with the 2023 assessment, this figure exhibits a precision approximately 800 times greater. Achieving a nuclear clock necessitates further refinement of this measurement's precision.
Upon observing the signal, "we naturally felt a surge of excitement," remarks physicist Ekkehard Peik from the National Metrology Institute of Germany in Braunschweig. "It marked the end of a lengthy quest." Peik initially introduced the notion of constructing nuclear clocks using thorium-229 in a 2003 publication he coauthored.
In the experiment, thorium-229 was integrated into a calcium fluoride crystal, a departure from the vacuum chamber containment typical in atomic clocks. The prospect of crafting future nuclear clocks from solid materials adds to their allure: "Conceivably, one could envision a significantly simplified, portable setup, liberating this clock from laboratory confines," suggests physicist Jun Ye from JILA in Boulder, Colorado, unaffiliated with the recent research.
As nuclear clocks operate on distinct principles from atomic counterparts, juxtaposing the two could facilitate fresh inquiries into fundamental physics (SN: 6/4/21). For instance, researchers could probe for fluctuations in the fundamental constants of the universe, presumed constants that regulate cosmic phenomena (SN: 11/2/16). Nuclear clocks might also inaugurate novel investigations into dark matter, enigmatic massive particles ubiquitous in the cosmos.
Constructing a nuclear clock entails substantial further research. Even upon completion, Ye asserts, "It will require years, if not decades, of effort to match the precision of atomic clocks." Nonetheless, "merely witnessing the transition represents a significant step forward."
