Researchers at TU Wien have achieved a significant advancement in precision timekeeping by creating the world’s first self-stabilizing nuclear clock. The device can operate continuously for over 24 hours without external intervention or reliance on conventional atomic clocks. This development represents a major step forward in the field of metrology, as nuclear clocks could eventually enable measurements of time and other physical quantities with unprecedented accuracy levels.
The breakthrough centers on properties of thorium atomic nuclei, which possess an unusually small energy gap between two nuclear energy states. This gap is small enough that laser light can trigger transitions between these states—a capability rarely found in other atomic nuclei. In April 2024, researchers led by Prof. Thorsten Schumm at TU Wien and Prof. Ekkehard Peik at PTB Braunschweig first demonstrated experimentally that laser beams could excite thorium nuclei. Following additional progress in fall 2024, they connected their thorium apparatus to a conventional optical atomic clock, establishing the basic principle of nuclear timekeeping.
The key innovation in the new system involves a self-regulating feedback mechanism. A special thorium-containing crystal developed at TU Wien is exposed to laser light. The thorium nuclei absorb laser light only at precisely the correct frequency; if the laser frequency drifts, absorption decreases, triggering automatic adjustments that maintain stability. This eliminates the need for a separate atomic clock to regulate the system.
Testing over a 24-hour period demonstrated impressive performance, with the prototype achieving a relative precision of approximately 10 to the minus 15—equivalent to an error of roughly one second over 30 million years. While this does not yet match the world’s leading optical atomic clocks, researchers describe the early-stage performance as exceptional. Scientists believe the precision can be substantially improved through more powerful lasers and higher-quality thorium crystals, potentially allowing nuclear clocks to eventually exceed the capabilities of existing atomic clock technology and establish new measurement standards.
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