Strontium clocks advantages, disadvantages, How accurate is the strontium atomic clock?

by Heba Soffar · May 5, 2025

Strontium clocks are optical atomic clocks that use the element strontium (Sr) to achieve extremely precise timekeeping, far more accurate than traditional cesium atomic clocks.

What are Strontium clocks?

Strontium clocks are a type of optical atomic clock that uses strontium atoms (specifically the isotope strontium-87) to measure time with extreme precision. It measures time by tracking the frequency of light needed to make electrons in a strontium atom jump between two energy levels. This frequency is very stable and extremely fast — about 429 trillion cycles per second (429 THz).

Strontium clock is far more accurate than traditional atomic clocks (like cesium clocks). It can detect tiny time differences due to changes in gravity, elevation, or motion. It helps in scientific research, GPS, time synchronization, and tests of Einstein’s theories.

How do Strontium clocks work?

Lasers cool strontium atoms to nearly absolute zero. To hold them still, they are trapped in a grid made of laser light—called an optical lattice. A second laser probes a specific energy transition in the atoms. The laser is “locked” to the frequency of that transition, creating an ultra-precise ticking rate.

Strontium atoms are trapped in a laser lattice (an optical lattice trap) and cooled to near absolute zero. A very stable laser probes a specific electronic transition in the strontium-87 isotope (specifically, between the ground state and an excited state). This transition occurs at an optical frequency—around 429 terahertz (THz)—which is much higher than the microwave frequencies used in cesium clocks. Higher frequency means more “ticks” per second, leading to higher precision.

Strontium clocks

Scientific applications of Strontium atoms

Testing fundamental physics, like gravitational time dilation (they can detect time differences caused by height changes of just a centimeter).
Contributing to global navigation systems.
Improving telecommunications and synchronization in scientific experiments.

Features of strontium optical clocks

Strontium clocks can keep time with an accuracy greater than 1 part in 10¹⁸, They would gain or lose only 1 second over 15 billion years. They are a candidate for redefining the SI second in the future. They use the ultra-narrow optical transition in strontium-87 atoms (~429 THz). This high frequency allows much finer resolution than microwave-based clocks.

Strontium atoms are held in place by a standing wave of laser light (optical lattice) to minimize motion-induced frequency shifts (Doppler effects). Atoms are cooled to microkelvin temperatures using laser cooling techniques to reduce thermal motion, increasing stability.

Strontium clocks can detect tiny changes in gravitational potential, such as moving the clock just a few centimeters in height. Frequency fluctuations are extremely low. Strontium clock is one of the most stable and reliable time standards currently known.

Strontium clocks are used in fundamental physics (e.g., testing general relativity, searching for variations in physical constants). They can be used in Global navigation and synchronization systems. They could be used in relativistic geodesy (measuring gravitational potential differences across Earth).

Advantages of Strontium Clocks

Accuracy better than 1 part in 10¹⁸ – among the most precise timekeepers ever built.
Extremely low drift over time, crucial for scientific measurements and synchronization.
Optical transitions (~429 THz) allow for finer time resolution than microwave clocks (like cesium).
Strontium clocks are sensitive to gravity, they can detect minute changes in altitude (as small as 1 cm) via gravitational time dilation. They are useful for relativistic geodesy.
Strontium clock enables fundamental physics tests, such as examining changes in fundamental constants or general relativity.
Strontium clock is a strong candidate for a future redefinition of the second in the SI system.

Disadvantages of Strontium Clocks

Strontium clock requires ultra-stable lasers, vacuum systems, and advanced laser cooling – much more complex than cesium clocks.
High-precision components and labor-intensive operations make them very expensive.
Lab-based systems; not yet easily miniaturized or portable for general use.
Strontium clocks are susceptible to temperature fluctuations, vibrations, and electromagnetic interference. They require strict environmental control.
Strontium clocks need highly trained personnel to operate and maintain them.