New nuclear clocks could become world's most accurate timekeepers

A pair of crystals illuminated with lasers could become the world's most accurate clocks.Two teams of scientists have made the world's first "nuclear clocks", which keep time by tracking tiny changes in the centre of atoms.Both clocks are so accurate that if they ran for 30 million years, they would only be off by a second.This accuracy does not surpass the best clocks in operation right now, but both teams are confident they will be able to improve their clocks significantly.The researchers have published their work in two papers in the journal Nature.University of New South Wales physicist Victor Flambaum said nuclear clocks had the potential to become the "most accurate instrument humans have ever built".Professor Flambaum said the studies, which he was not involved with, represented an exciting step forward.The clocks could be used to improve technology such as GPS, mining surveys and solve physics mysteries.How does a nuclear clock work?Atoms, which compose all the matter we interact with, are made from a "nucleus" containing a dense cluster of protons and neutrons, surrounded by a spacious cloud of electrons.Atomic clocks, currently the most accurate measures of time in the world, work by tracking changes in the electrons around the nucleus of a caesium atom.But these clocks are approaching a point where it is physically impossible to make them more accurate.Atoms are made from a dense "nucleus" of clustered protons and neutrons (red and blue), surrounded by a cloud of moving electrons (grey) which can be thousands of times larger in size. (Pixabay: geralt)Nuclear clocks use a similar logic to atomic clocks, but they track even smaller changes in the nucleus of an atom."A nucleus is very small compared to [a whole] atom," Professor Flambaum said.Because it is thousands of times smaller, a nucleus could be used to measure much more subtle changes in time, leading to a more accurate clock.Why couldn't we build nuclear clocks before?Nuclear clocks have been theorised for more than two decades, but until recently technological and theoretical constraints have made them impossible to build.Thorsten Schumm, co-author on one of the new studies and a physicist at Vienna University of Technology, said the main turning point in his team's research came a couple of years ago.In early 2024 the team used a laser to produce the predicted change in an atomic nucleus that would allow time to be measured.Professor Flambaum said progress had been "very rapid" since that discovery.The TU Wien team showed in 2024 that atomic nuclei could change states when prompted by a laser, giving them the "tick" of a nuclear clock. (Supplied: Matthias Heisler/TU Wien)Tsinghua University physicist and study co-author Shiqian Ding said his team needed to solve several different problems to make the nuclear clock.The problems included making a material with the right clock nuclei inside it and developing lasers precise enough to produce reliable changes."There was no single step that suddenly made the clock possible," Dr Ding said.What is a nuclear clock made from?A specific type of thorium atom, thorium-229, has the properties to make it usable as a timekeeper.Both teams grew crystals containing thorium-229, then suspended them under ultra-precise lasers that could produce tiny, nucleus-sized "ticks" in the thorium.The researchers also have plans to improve nuclear clocks so they can outperform atomic clocks.Atomic clocks at Australia's National Measurement Institute. (Supplied: National Measurement Institute)Professor Schumm said thorium-229 had potential to be more stable than atomic clocks, meaning nuclear clocks could become very small and practical to move around."We envision a chip-scale device," he said.What would nuclear clocks be used for?Nuclear clocks could be used to improve navigation systems such as GPS, which has driven military interest in the latest iterations of atomic clocks.Professor Flambaum said nuclear clocks could be accurate enough to measure the manipulation of time by gravity, per Einstein's theories of relativity.This could make them useful in mining exploration or earthquake prediction.“By measuring, accurately, the gradient of gravitational fields, we can see what is under the earth,” Professor Flambaum said.The super-accurate timekeeping could also be used in physics research, particularly in probing mysterious dark matter."I am particularly excited about using nuclear clocks to test fundamental physics," Dr Ding said.Professor Schumm's team has already used their nuclear clock to detect evidence of dark matter, as proof of concept.He is planning to install a second nuclear clock in Innsbruck within a year, to accompany the clock in Vienna and measure subtle changes in Earth's movement around the Sun.Professor Flambaum said there was a "race" among several other groups to make practical nuclear clocks and that any one of them could be the first to outperform atomic clocks."The progress is so fast, I expect it will be soon," he said.