World’s 1st thorium-powered nuclear clock unveiled for ultraprecise timekeeping

The world’s first nuclear clock could begin ticking soon after researchers at JILA, a joint institute of the National Institute of Standards and Technology (NIST) and the University of Colorado Boulder, successfully demonstrated the workings of all the components needed to build one.

Unlike the atomic clock, which uses vibrations from an atom to measure time, a nuclear clock uses signals from the nucleus of an atom for timekeeping.

Atomic clocks are the most precise method available to measure time. They coordinate international time zones and synchronize the Internet and financial transactions.

It would be easy to assume that the precision of an atomic clock may not have a role in day-to-day life, but even services like global positioning systems (GPS), digital communication, and internet speeds rely on it.

Even as newer atomic clocks are being developed and older ones improved upon, researchers at JILA are keen to build a nuclear clock. This clock can deliver much higher precision by measuring time using the energy jumps from an atom’s core.

“The nuclear clock’s energy level is closely coupled to strong forces in the nucleus while atomic clocks mainly depend on electromagnetic forces,” Chuankun Zhang, a physicist at JILA, told Interesting Engineering in an email. “Thus, a nuclear-atomic clock comparison can provide sensitive tests for fundamental physics.”

Working with thorium

Nuclear clocks are more accurate than their atomic counterparts because the nucleus is less affected by outside disturbances like stray magnetic fields. However, making a nuclear clock isn’t straightforward because the energy jumps needed for a nuclear clock to tick can only be created by high-energy coherent X-rays, and current laser technology cannot produce them.

So, researchers focused their attention on thorium-229 since its nucleus needs a smaller energy jump than any other known atom, requiring ultraviolet light, which has lower energy than X-rays.

Although this phenomenon has been known since 1976, it was only in April this year that scientists succeeded in using ultraviolet lasers that could achieve a jump within a thorium nucleus.

Scientists at JILA coupled their previous atomic clock designs with thorium nuclei and have designed other required components to make a nuclear clock.

Making a nuclear clock

The researchers have not assembled the nuclear clock yet, but they have all the components necessary to make one if necessary. The team focused on measuring the frequency of the jump more precisely.

“We managed to improve the accuracy of this measurement by a million times compared to previous measurements,” added Zhang in the email. “This allows us to resolve the quantum energy sublevels of this nuclear transition for the first time.”

When asked when the clock would be ready, Zhang said, “We are working on improving the spectroscopy resolution further and evaluating systematic shifts of the transition so we can get better clock accuracy when we start operating it as a clock.”

“Essentially, we have all the parts for a nuclear clock already demonstrated in the lab. We have not used them for the actual clock operation, but there’s no technical difficulty in building one any day now.”

An added advantage of using a nuclear clock over an atomic clock would be its simplicity of working.

“We can probe the nuclear transition in a solid-state system, which would allow us to build a much simpler clock than today’s atomic clocks without needing technologies like an ultrahigh vacuum, laser cooling, and trapping, etc.,” added Zhang in the email.

“Such a simple clock could then be useful for precision timekeeping outside research labs.”