The most precise clocks ever built are so accurate that they can detect the gravitational pull of a passing rain shower warping the Earth’s crust. These optical clocks keep time more than ten thousand times better than the microwave atomic clocks that currently underpin satellite navigation and ultrafast broadband. But their extraordinary precision is useless if it cannot be delivered to the people who need it. Existing methods—microwave links via satellite, or dedicated optical fibre cables—are either too slow, too expensive, or too short-range for intercontinental use. ICON will combine world-leading transportable optical clocks with space-based optical links to solve that transfer problem. If the project succeeds, the first beneficiaries will be researchers who rely on precision oscillators for experiments in fundamental physics. In the longer term, the same technology could make navigation systems dramatically more accurate, synchronise financial trading networks, or tighten the timing of data transmission across continents. The work also includes making the clocks more compact and robust using atom chip concepts, which is a necessary step toward moving these devices out of specialist laboratories and into practical infrastructure.
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Time is the quantity, which can be measured to the highest precision of all metrological quantities. We all benefit from this extraordinary precision in our everyday lives, as precision time enables synchronization of data packets in ultrafast broadband communication and the determination of our position by computing the flight times of radiofrequency signals in Satellite Navigation to nanosecond precision. These economically important applications rely on microwave atomic clocks, which in their commercial form are precise to 1 part in 10^14. We are currently facing a revolution in timing accuracy due to the invention of optical clocks and accessible ways of counting optical frequencies, which has already been recognised by the Nobel Price in Physics in 2005. These novel clocks already reach stabilities beyond 1 part in 10^18, more than 4 orders of magnitude beyond the state-of-the art. However, while the clock technology is progressing rapidly, there is still a lot to learn about how such a precision can be transferred to the user community in a practical and efficient way. Microwave links, such as used in current satellite time transfers, are impractically slow for such precision, while optical fibre links need expensive dedicated fibre connections and are limited to a few 100 km, making intercontinental connections impractical. In addition, at 10^-18 precision, effects such as general relativity coupling gravity to frequency are coming into play and make the transfer dependent on deformation of the continental plates in Earth tides and larger rain falls. ICON brings together world leading transportable optical clocks and world leading optical link space infrastructure to explore the limits of precision time transfer. Including work on making transportable clocks more compact and robust with world-leading atom chip concepts, we are aiming at bringing precision time to everyone - first researchers relying on precision oscillators and later in commercial applications for the benefit of wider society.
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