Scientists have achieved a significant milestone in timekeeping, constructing the first operational nuclear clock. This innovative device, developed by Thorsten Schumm and his team at the Vienna University of Technology in Austria, harnesses the precise vibrations of atomic nuclei, specifically those of radioactive thorium, to measure time. The concept of a nuclear clock has been a long-standing ambition in physics, with researchers pursuing its realisation for over two decades.
Traditional atomic clocks, which currently represent the pinnacle of timekeeping accuracy, rely on the energy transitions of electrons orbiting an atomic nucleus. These clocks are incredibly precise, losing only a few seconds over a billion years, and are fundamental to technologies like GPS and global communication networks. However, the theoretical precision offered by nuclear clocks, which utilise the nucleus itself, is far greater due to the nucleus's higher energy levels and its shielding from external electromagnetic interference. Experts suggest nuclear clocks could achieve stabilities of mere seconds over hundreds of billions of years, vastly exceeding the age of the universe.
A major hurdle in developing nuclear clocks has been the immense energy required to excite most atomic nuclei. Thorium, however, presents a unique exception, requiring comparatively less energy for excitation. The discovery in 2023 of the specific laser frequency capable of exciting thorium's nucleus provided the crucial insight needed for this breakthrough. The new clock embeds thorium within a calcium fluoride crystal and uses an ultraviolet laser that oscillates between two frequencies, acting as the clock's 'tick'. A feedback mechanism ensures the laser is precisely tuned, maintaining accuracy.
While this initial prototype does not yet match the stability of the most advanced atomic clocks, currently losing tens of seconds per billion years, its significance lies in proving the principle. The research team views it as a foundational step, with future refinements involving superior lasers and electronics expected to enhance its performance significantly. Ekkehard Peik from PTB, the German national metrology institute, noted the system's impressive ability to run autonomously for 24 hours without human intervention, a rapid achievement for an optical clock prototype.
The implications of such ultra-precise timekeeping extend beyond mere accuracy. A nuclear clock's enhanced stability and unique properties, particularly its nucleus being shielded from electronic chaos, could enable physicists to conduct unprecedented experiments. These include the potential to probe fundamental laws of physics and search for elusive particles such as dark matter, opening new avenues in scientific discovery that current atomic clocks cannot facilitate.
Source: Vienna University of Technology