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This connection was first established in 2015 between the Center for Physical Sciences and Technology (FTMC) and Poland’s Central Office of Measures (Główny Urząd Miar, GUM). Both metrology institutes monitor and compare the performance of atomic clocks. The link was created with the help of academic networks: Lithuania’s LITNET and Poland's PIONIER.

 

Dr Miškinis heads the Time and Frequency Standard Laboratory of Lithuania’s National Metrology Institute (NMI), a role fulfilled by FTMC. While the institutional structure may sound complex, the atomic clocks operating in the lab are what truly matter. Here, the phrase "every second counts" takes on a whole new level of significance: these devices measure time with billionths-of-a-second precision. This is critical not only for maintaining global time synchronization but also for high-precision operations like navigation systems and international banking transactions.

 

 

 

The most accurate - atomic - clocks in Lithuania work as follows: microwaves are emitted into a cesium atom, and based on its interaction response, precise and regular time signals are generated.

 

There are approximately 600 atomic clocks worldwide, which communicate via satellites. However, Lithuania and Poland are already using a fiber-optic link as well, and Europe now aims to interconnect all atomic and optical clocks across the continent via optical fibers.

 

Why is this important?

 

 

To understand the importance of this, let’s rewind to March 25-26, when FTMC hosted the annual meeting of the EURAMET Technical Committee for Time and Frequency. The highlight of the event was the signing of a memorandum of understanding to participate in a major European initiative called FOREST (Fiber-based Optical netwoRk for European Science and Technology).

 

“This network would connect scientific institutions across Europe and interlink atomic and optical clocks while enabling quantum phenomena research. It’s very important because standard time and frequency signals will be transmitted via optical fiber, allowing even more accurate clock comparisons,” explains Dr Miškinis, who organized the conference.

 

 

 

According to the scientist, various bilateral fiber-based clock comparison projects have already been established between France and Germany, Italy and Austria, and, as mentioned, Lithuania and Poland. But globally, satellite-based synchronization remains dominant. While this technology is effective, it can be disrupted or disabled by natural phenomena (such as solar flares), unintentional interference, or even malicious sabotage.

 

FOREST’s authors warn that such events could have catastrophic impacts on the economy and critical infrastructure. This concern has motivated lawmakers - including the European Commission - to explore alternative solutions.

 

And fiber optics seem to offer a reliable alternative: they are more stable than satellite connections (much like wired internet tends to be more stable than Wi-Fi) and, when buried underground, are less vulnerable to external threats.

 

“Furthermore, optical clocks, whose development is accelerating globally, can no longer be compared via satellite. Their signals simply cannot be transmitted that way,” adds Dr Miškinis.

 

 

 

What makes optical clocks so special? Using this technology, electrons jump between energy levels in atoms, emitting light (an optical signal) at extremely regular intervals. Because the frequency of optical signals is significantly higher than microwave signals, optical clocks can measure time thousands of times more precisely than traditional atomic clocks!

 

“We don’t yet have an optical clock in Lithuania. The closest one is in Toruń, Poland. It’s experimental and connected via fiber to Germany’s optical clock. Tests conducted this autumn showed that the fiber link transmits the optical signal with very minor instabilities,” says the FTMC physicist.

 

He also highlights another potential benefit of FOREST: helping seismologists.

 

“By analyzing data from clock comparisons, we can detect what’s happening in the fiber itself. Since these cables stretch thousands of kilometers, it’s possible to pick up on earthquakes, explosions, or other vibrations,” he explains.

 

 

According to Dr Miškinis, this initiative will benefit not only science but society as a whole.

 

“For 5G and 6G networks to work effectively, stable synchronization between base stations and internal device clocks is essential. This can only be achieved with extremely stable frequency signals - and one source of such signals could be an optical clock. Atomic clocks might be just barely sufficient, but optical clocks would be ideal,” he emphasizes.

 

 

 

It is not yet clear when exactly this ambitious plan (to connect Europe’s atomic and optical clocks via fiber) will be fully implemented. If the FOREST program is approved, calls for concrete project proposals will begin. As a full-fledged participant, Lithuania will be eligible to submit applications and receive funding.

 

“Interestingly, Lithuania is the northernmost country to have joined this initiative. We aim to extend the fiber network to Helsinki, but there is currently no high-quality fiber-optic link from Lithuania through Latvia to Tallinn. Some technical issues need to be resolved. We hope LITNET’s (the Lithuanian Research and Study Computer Network) participation in this project will help address them.

 

Finland and Sweden already have a solid mutual network, and among the Baltic countries, Lithuania is the leader,” notes Rimantas Miškinis, head of the Time and Frequency Standard Laboratory at the National Metrology Institute.