West LA Times

UCLA physicists have achieved a breakthrough in atomic clock technology by using the nucleus of thorium-229 embedded in a transparent crystal to absorb and emit photons, similar to electron behavior in atoms. This advancement promises the development of highly accurate atomic clocks, potentially revising fundamental physics laws. However, thorium-229-doped crystals are scarce and radioactive.

A team of UCLA chemists and physicists has addressed this issue with thin films derived from a thorium-229 precursor. The new method employs less radioactive material and is as harmless as a banana. These films replicate the laser-driven nuclear excitation necessary for nuclear clocks and can be scaled for quantum optics applications.

The innovative approach involves using a dry nitrate parent material of thorium-229 dissolved in ultrapure water, followed by the addition of hydrogen fluoride. This process yields micrograms of thorium-229 precipitate, which condenses on sapphire and magnesium fluoride surfaces after heating.

Co-author Anastassia Alexandrova stated, "A key advantage to using a parent material — thorium fluoride — is that all the thorium nuclei are in the same local atomic environments and experience the same electric field at the nuclei." This uniformity ensures stable excitation energies, enhancing clock accuracy.

The core mechanism of any clock is its oscillator, defining time by oscillation cycles. In thorium nuclear clocks, each second corresponds to over two quadrillion excitation cycles. Thin films provide stability for these cycles, facilitating smaller, more affordable devices.

Existing atomic clocks rely on electron-based systems requiring substantial equipment. A thorium-based clock would be compact, robust, portable, and precise. Beyond commercial use, this innovation could unveil insights into atomic properties and interactions with energy and space-time laws.