Taking a second to change the time 

Time is almost up on the way we track each second of the day, with optical atomic clocks set to redefine the way the world measures one second in the near future. 

Researchers from Adelaide University worked with the National Institute of Standards and Technology (NIST) in the United States and the National Physical Laboratory (NPL) in the United Kingdom to review the future of the next generation of timekeeping.  

They found that development is happening at such a fast rate that optical atomic clocks are well positioned to become the gold standard for timekeeping within the next few years, provided some technical challenges can be addressed.  

“Optical atomic clocks have advanced rapidly over the past decade, to the point where they are now one of the most precise measurement tools ever built. They’re more accurate than the best microwave atomic clocks and can even work outside the lab – this is a place that conventional atomic clocks have trouble venturing,” said co-author Professor Andre Luiten from Adelaide University’s Institute for Photonics and Advanced Sensing.  

Optical atomic clocks are made from laser-cooled trapped ions and atoms. When scientists repeatedly probe the atoms with a laser, they respond only at a special frequency which can be converted into ticks to track time accurately.    

The review into the next generation technology, which has been published in the journal Optica, outlines the key features, progress that’s been made over the past decade, challenges and future applications.  

“A decade ago, optical atomic clocks had no impact on the steering of international time. Today, at least ten have been approved for use,” said Professor Luiten.  

A roadmap for redefining how the second is measured is underway, but researchers have noted other potential uses for optical atomic clocks, including as gravity sensors that can aid in creating an international height reference system that’s not based on sea level. Their precision and sensitivity also positions them as a useful tool for testing fundamental physics such as dark matter.  

They could be relied on to maintain accurate time during satellite outages caused by solar storms or malicious attacks. This latter opportunity is seeing an outpouring of commercial interest in optical clocks, including from Adelaide University spin-out, QuantX Labs.   

Despite the rapid development of this technology, the review does identify several key challenges. These include limitations to the operational capability of optical atomic clocks, with many still operating intermittently. Decisions around how to redefine the second also need to be made, including if a single type of optical atomic clock or a group are the most reliable way to replace caesium fountain clocks, with direct comparisons needed.  

Supply chains for critical components are also underdeveloped, resulting in higher costs, however, researchers believe progress in quantum computing and bioscience are likely to lead to more affordable and accessible systems in the future.  

“Optical clocks have advanced at an extraordinary rate, improving by more than a factor of 100 every decade, thanks to breakthroughs in atomic physics and laser science. By showcasing their performance, emerging roles, and the challenges that lie ahead, we hope to inspire a wider community to explore and technically build on nature’s most precise timekeepers," said lead author Tara Fortier from NIST. NIST provides the official time for the United States and plays a role in setting the world’s time scale.  

 The research has been supported by the National Institute of Science and Technology Physical Measurement Laboratory, Defence Science and Technology Group and the Australian Research Council Centre of Excellence in Optical Microcombs for Breakthrough Science.