Researchers at TU Wien have achieved a significant breakthrough in precision timekeeping by creating a self-regulating nuclear clock based on thorium atomic nuclei. The device represents the culmination of decades of research into alternative methods for measuring time with unprecedented accuracy. Unlike earlier experimental versions, this prototype can maintain stable operation without relying on conventional atomic clocks for calibration.
The innovation centers on a unique property of thorium nuclei, which possess two energy states separated by an unusually small energy gap. This characteristic allows scientists to manipulate these nuclear states using laser light, a capability not readily available with most other atomic nuclei. Key milestones included the experimental identification of the relevant nuclear transition in April 2024, followed by successful coupling of thorium excitation to an optical atomic clock in fall 2024. These earlier achievements demonstrated the fundamental feasibility of using thorium nuclei as a timekeeping reference.
The recent breakthrough involves a self-stabilizing mechanism in which thorium nuclei absorb laser light only at precisely the correct frequency. When the laser frequency begins to drift due to environmental factors like temperature fluctuations, the nuclei absorb less light, triggering automatic feedback that restores the laser to its proper frequency. This continuous regulation allows the clock to maintain accuracy without external intervention, a crucial requirement for practical applications.
Testing over a 24-hour period demonstrated a relative precision of approximately 10 to the minus 15, translating to an error of roughly one second over 30 million years. While this performance falls short of the world’s leading optical atomic clocks, researchers characterize it as an exceptional result for an early prototype. The team believes substantial improvements are achievable through more powerful lasers and higher-quality thorium crystals, potentially enabling nuclear clocks to eventually exceed the performance of existing atomic clocks and establish new standards for precision measurement science.
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