#excessmicromotion

Quantum Clocks

NIST researchers have developed an atomic clock that can measure time to the 19th decimal place, a remarkable achievement in time measurement. After 20 years of hard labour, this record is 41% more accurate than the previous one.

Trapped aluminium ions make the “quantum logic clock” 2.6 times more stable than earlier ion clocks. The July 14, 2025 publication of this finding in Physical Review Letters contributes to global efforts to precisely redefine the standard second and may lead to new scientific and technological uses.

Understanding NIST and QLC

NIST, a US federal body, advances measuring science, standards, and technology. Scientific progress depends on its metrological work, which measures frequency and time.

This greater accuracy is based on quantum logic spectroscopy. The clock uses an electrically charged aluminium ion due of its high-frequency “ticking” rate and resistance to temperature and magnetic fields. Atomic clocks require direct laser probing and cooling of aluminium ions, which are notoriously difficult.

The researchers built a “buddy system” of magnesium and aluminium ions to avoid this. Lasers can control magnesium, however it has poor timing qualities compared to aluminium. By mediating, the magnesium ion helps the aluminium ion cool and read out its quantum states through motion. This intricate coordination lets the aluminium ion “tick” unaltered.

Surmounting Major Engineering Challenges

To attain this unequalled accuracy, numerous interdependent systems have to be meticulously optimised, overcoming key engineering barriers that had limited ion clocks.

Redesigned Ion Trap: Overcoming "excess micromotion," small, unintended motions of the ions inside the trap that vary their ticking rate and affect clock accuracy, was difficult. Additional fields from electrical mismatches in the earlier trap design disturbed ions. The scientists placed the trap on a thicker diamond wafer by carefully rebuilding the trap and changing the gold electrode coverings. This intervention reduced electrical resistance, adjusted electric field imbalances, and reduced disruptive ion motions to preserve the aluminium ion's ticking rate.

Titanium Vacuum Chamber: Background gas contamination, notably residual hydrogen gas, prohibited prior ion clocks from working by diffusing from steel vacuum chambers and colliding with ions. For this, the researchers designed the vacuum chamber from titanium, which outgasses less. This crucial enhancement cut leftover hydrogen gas by 150 times, extended operational endurance from 30 minutes to days, and standardised ion monitoring conditions. Ultrastable Laser Integration: JILA, a joint NIST-CU Boulder institute, helped increase precision and stability. A world-stable laser from Jun Ye's lab was employed. This ultrastable laser was supplied to NIST's frequency comb over 3.6 km via fibre optic cables. This process “transferred” JILA laser stability to the aluminium clock laser, allowing comparisons. Limiting quantum fluctuations during measurement reduced the time needed to achieve 19-decimal place precision from three weeks to 1.5 days. It also allowed researchers to study ions for a second instead of 150 milliseconds.

In addition to these fundamental advances, significant efforts were made to characterise and decrease minute effects like thermal fluctuations, electromagnetic interference, and vibrations, which lowered accuracy.

Wide-ranging uses and prospects

Due to its enhanced stability and reduced measurement time, this new clock can be used for many purposes beyond precise timekeeping.

This development aids global efforts to define the standard second. Precision Geodesy: The clock's accuracy allows for unparalleled resolution in studying Earth's geodesy—its gravitational field, form, and orientation. Detecting minute time shifts that represent minor mass distribution changes may help us comprehend plate tectonics, glacier movement, and groundwater oscillations.

basic Physics Investigations: The clock allows for the search for basic constant changes outside the Standard Model, which requires precise timing. The shorter average time needed to acquire accuracy allows longer observation periods and greater sensitivity to changes.

Quantum Technology Testbed: The clock's upgrades make it a better testbed for quantum physics experiments and quantum technology equipment. Rapidly analysing and changing the clock's performance allows high-precision, portable timekeeping, which may affect satellite navigation and secure communications.