At the Atomic Institute of the Vienna University of Technology, we aim to build the most precise clock in the world, a nuclear clock. Its core: Thorium, specifically the isotope Thorium-229.
Atomic clocks measure time so precisely that they are off by only one second in 20 billion years. While this sounds very accurate, it is still not always accurate enough. Navigation satellites with atomic clocks on board help determine one's location on Earth within a radius of about ten meters. But would you get into an autonomous car that just drives ten meters into an intersection?
With nuclear clocks, we can improve time measurement. Instead of observing electron oscillations like in atomic clocks, we observe changes in the atomic nucleus. These are hardly influenced by external factors such as magnetic fields or temperature fluctuations.
Thorium-229 requires comparatively little energy to trigger these changes. Additionally, its frequency is very high, with 2 quadrillion oscillations per second. This allows for precise measurements and makes thorium the ideal timekeeper for a nuclear clock.
Typically, experimental physicists try to grow large-volume crystals. We want the opposite: small crystals where the laser light exclusively excites the thorium nuclei.
In the fall of 2024, together with US colleagues, we presented the first prototype of a nuclear clock with our crystal as the centerpiece. We have proven that thorium is the right material for ultra-high precision measurements. Now, the focus is mainly on technical development work, such as further shrinking the crystals—so much so that in the end, perhaps even a single thorium ion is sufficient for measurements.