Quantum Clocks
An atomic clock that can measure time with previously unheard-of accuracy, down to the 19th decimal place, has been unveiled by researchers at the National Institute of Standards and Technology (NIST), marking a groundbreaking accomplishment in time measurement. This milestone is the result of 20 years of hard work and marks a 41% increase in accuracy over the previous record.
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The “quantum logic clock” uses trapped aluminium ions and is 2.6 times more stable than previous ion clocks. The July 14, 2025 publication of this breakthrough in Physical Review Letters adds to global efforts to precisely redefine the standard second and could lead to new scientific and technological uses.
Understanding NIST and the Quantum Logic Clock
A key player in the advancement of measuring science, standards, and technology is NIST, an official agency of the US government. Its metrological activity, which includes measuring frequency and time, is essential to the advancement of science.
Quantum logic spectroscopy is the fundamental idea underlying this increased degree of accuracy. Because of its remarkably constant and high-frequency “ticking” rate, as well as its resilience to external factors like temperature and magnetic fields, the clock makes use of an electrically charged aluminium ion. However, direct laser probing and cooling of aluminium ions both crucial methods for atomic clocks are infamously challenging.
The researchers used a “buddy system” to get around this, pairing the magnesium ion with the aluminium ion. Magnesium is easily controlled with lasers, although it does not have the same ideal timing properties as aluminium. By acting as a mediator, the magnesium ion makes it easier for the aluminium ion to cool and for its quantum states to be read out by its motion. Because of this complex coordination, the aluminium ion is able to “tick” unaffected.
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Overcoming Significant Engineering Challenges
In order to achieve this unmatched accuracy, several interdependent systems had to be carefully refined, overcoming major engineering obstacles that have hitherto restricted ion clocks.
- Redesigned Ion Trap: Overcoming “excess micromotion” small, inadvertent movements of the ions inside the trap that change their ticking rate and compromise the accuracy of the clock was a significant challenge. The ions were disrupted by additional fields produced by electrical imbalances in the earlier trap design. By carefully redesigning the trap and altering the gold electrode coatings, the team was able to put it on a thicker diamond wafer. The faithfulness of the aluminium ion’s ticking rate was maintained by this intervention, which corrected electric field imbalances, decreased electrical resistance, and minimised these disruptive ion motions.
- Titanium Vacuum Chamber: Background gas contamination, especially residual hydrogen gas, prevented earlier ion clocks from working by diffusing from steel vacuum chambers and colliding with ions. To solve this, the researchers built the vacuum chamber from titanium, which outgasses less. This essential improvement reduced leftover hydrogen gas by 150 times, increased continuous operational endurance from 30 minutes to many days, and standardized ion measuring conditions.
- Ultrastable Laser Integration: Working with experts at JILA, a joint institute of NIST and the University of Colorado Boulder, further notable improvements in precision and stability were made. Specifically, one of the most stable lasers in the world, from Jun Ye’s lab, was used. Over 3.6 km, this ultrastable laser was sent to a frequency comb at NIST via fibre optic cables. This procedure successfully “transferred” the stability of the JILA laser to the aluminium clock laser and made comparisons possible. By limiting the accumulation of quantum fluctuations during measurement, this invention significantly shortened the time needed to obtain 19-decimal place precision from three weeks to just one and a half days. In addition, it gave the researchers the opportunity to examine the ions for a full second as opposed to their earlier 150 millisecond limit.
- Systematic Refinement: In addition to these fundamental advancements, careful consideration was given to characterising and reducing a variety of minute effects, including as thermal fluctuations, electromagnetic interference, and even vibrations, which together reduced accuracy.
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Far-Reaching Applications and Future Prospects
Beyond the immediate objective of extremely accurate timekeeping, a wide range of prospective applications are made possible by this new clock’s improved stability and substantially shorter measurement time.
- Redefining the Second: This development contributes to the global effort to define the standard second more precisely.
- Precision Geodesy: The clock’s accuracy allows for unprecedented resolution in investigating minute changes in Earth’s geodesy, which is its gravitational field, form, and orientation. To detect minute time shifts that represent small mass distribution changes may improve our understanding of plate tectonics, glacier movement, and groundwater oscillations.
- Fundamental Physics Investigations: The clock enhances the possibility of investigating physics outside of the Standard Model, such as the hunt for changes in fundamental constants, which requires the utmost timing accuracy. Longer observation periods and more sensitivity to possible fluctuations are made possible by the reduction in the average time required to reach such precision.
- Quantum Technology Testbed: The clock’s improvements significantly increase its usefulness as a testbed for investigating novel ideas in quantum physics and creating instruments for upcoming quantum technology. Rapidly evaluating and adjusting the clock’s performance also creates opportunities for high-precision, portable timekeeping, which may have an effect on secure communications and satellite navigation.
By increasing the number of clock ions and investigating the advantages of quantum entanglement, the research team which includes project leader David Hume and first author Mason Marshall plans to scale up the system in the future. Multiple ion entanglement may further decrease quantum fluctuations and improve measurement accuracy, which could result in even higher timing accuracy and open the door to revolutionary developments in metrology and basic physics.
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