A new clock tied to the orbiting of a neutron around an atomic nucleus could have such unprecedented accuracy that it neither gains nor loses 1/20th of a second in 14 billion years - basically, you wouldn't have needed to reset your watch yet even if you had been around at the beginning of the Universe.
Atomic clocks are already in use for GPS navigation systems and applications like system synchronization in particle accelerators - you can even sync your PC to them, though your PC will be inaccurate again in an hour. The proposed single-ion clock do those atomic clocks one better and be accurate to 19 decimal places, nearly 100 times more accurate than the best ones in use now. That gives you some idea that clocks are already really, really accurate.
Because the neutron is held tightly to the nucleus, its oscillation rate is mostly unaffected by external perturbations. The electrons in atomic clocks are much more loosely bound. 'Much more' being relative, like time itself. To anyone outside high-end physics that is still really good.
NIST postdoctoral researcher James Chin-wen Chou with the world's most precise clock, based on the vibrations of a single aluminum ion (electrically charged atom). The ion is trapped inside the metal cylinder (center right). Credit: J. Burrus/NIST
Still, science is all about not settling for good enough. "With these clocks currently pushing up against significant accuracy limitations, a next-generation system is desired to explore the realms of extreme measurement precision and further diversified applications unreachable by atomic clocks," says Professor Victor Flambaum, Head of Theoretical Physics at the University of New South Wales, who co-authored the paper (upcoming - no citation yet) in Physical Review Letters. "Atomic clocks use the orbiting electrons of an atom as the clock pendulum. But we have shown that by using lasers to orient the electrons in a very specific way, one can use the orbiting neutron of an atomic nucleus as the clock pendulum, making a so-called nuclear clock with unparalleled accuracy."