The world's first working nuclear clock, powered by thorium-229, has been developed, marking a significant milestone in the field of timekeeping and fundamental physics. This groundbreaking achievement not only showcases the potential of nuclear transitions in atomic clocks but also opens up new avenues for exploring the fundamental forces that shape our universe.
What makes this clock truly remarkable is its ability to detect tiny changes in the forces that govern the universe. By utilizing a nuclear transition in thorium-229, the clock offers a unique sensitivity to fluctuations in fundamental constants, such as the fine-structure constant and quark masses. This sensitivity is crucial for searching for dark matter, as it can detect periodic oscillations or slow drifts in these constants, which are predicted by certain theories.
The clock's performance is impressive, demonstrating shot-noise-limited fractional frequency instability of 3 × 10^-12/√(τ/s) over one day of continuous operation. This level of stability is achieved through a combination of continuous absorption spectroscopy and the use of a subharmonic of the 148 nm radiation, which allows for precise measurements and tracking of any drift.
One of the key challenges in building atomic clocks is noise control. The researchers addressed this by adjusting the frequency of the laser corrections to the thorium resonance, ensuring a stable and reliable clock. Additionally, the use of continuous absorption spectroscopy provided a practical solution by allowing continuous probing without waiting for the thorium isomer's long lifetime, resulting in three orders of magnitude more signal photons per second.
The clock's performance is further enhanced by its ability to operate for an extended period without intervention. During a 20-second operating mode, the researchers searched for periodic signals between 20 seconds and 1 day, placing new upper limits on possible dark-matter couplings. The clock's sensitivity is comparable to the best atomic-clock comparisons, pushing the boundaries of parameter space for couplings tied to the strong force and quark masses.
Looking ahead, the researchers envision several improvements to further enhance the clock's performance. Increasing laser power, using longer crystals, and exploring other crystal hosts can improve signal-to-noise and reduce linewidth. Additionally, employing spinless solids can suppress magnetic broadening from neighboring fluorine nuclei, leading to a more precise and stable clock.
The practical implications of this research are far-reaching. The thorium-229 clock not only provides a new tool for testing the stability of nature's constants but also offers a promising platform for developing solid-state nuclear clocks. These clocks could potentially rival the best optical atomic clocks while being less susceptible to external disturbances, making them valuable for probing physics beyond the standard model.
In conclusion, the development of the world's first working nuclear clock powered by thorium-229 is a significant achievement in both timekeeping and fundamental physics. It opens up new possibilities for exploring the universe's fundamental forces and has the potential to revolutionize how we measure time, offering a more accurate and robust clock than ever before.
