Fascination with technology Just a second in 30 million years

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In our "Fascination with Technology" section, we present impressive projects from research and development to designers every week. Today: a laser clock that is a hundred times more accurate than today's satellite clocks.

A new laser clock from the German Aerospace Center (DLR) has achieved a peak level of accuracy for optical clocks with gas cells: it would only be off by one second in 30 million years. The quantum properties of iodine molecules set the pace for the laser clock.

It deviates less than 100 picoseconds per day from the so-called world time.

Prof. Claus Braxmaier from the DLR Institute of Quantum Technologies

Time is not the same as time

In response to the question, what is time, Albert Einstein once said: "Time is what you read on the clock." It depends on the accuracy of the clock. How well satellite navigation, internet, earth observation or financial services work also depends on how precisely the necessary time information is during data transmission. Satellite clocks provide time signals that, for example, can be used to determine positions on the earth or synchronize communication networks.

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Space-suitable laser clocks can provide more accurate time information in the future to make satellite services for communication and navigation more efficient and precise. Laser-optical clocks are around a hundred times more accurate than current microwave-based satellite clocks due to their higher clock frequency.

Laser clock achieves peak value

With its leading expertise in quantum technologies in space, the DLR has developed the highly precise laser clock in the Compasso project. "It deviates less than 100 picoseconds per day from so-called world time. A picosecond is a millionth part of a millionth of a second. This deviation corresponds to one second in 30 million years," explains Prof. Claus Braxmaier from the DLR Institute for Quantum Technologies in Ulm, Germany. "We thereby close the gap between the accuracy of conventional satellite clocks and the large, heavy high-end atomic clocks that determine our world time in national metrology institutes."

Quantum physics sets the pace

The pace of the laser clock is set by quantum physics. For this, the wavelength of a laser is tuned to a specific vibration of iodine molecules in a gas cell. The pace of this vibration depends only on the quantum mechanical properties of the iodine. This device-independent reference allows the high accuracy of the optical clock to be achieved.

In the clock laboratory of the DLR Institute for Communication and Navigation, the DLR researchers have further developed the laser clock to its current accuracy and compared it with another precision clock, a so-called hydrogen maser. This is a type of laser in the microwave range. "By superimposing the time signals of both clocks, we can count the individual beats of the laser clock like with a stopwatch. These follow each other at a frequency of 10 megahertz, that's 10 million beats per second," explains Claus Braxmaier. "In this way, we were able to determine both the rate accuracy and the precision of our laser clock. The more precise a clock is, the more uniform is its beat. The rate accuracy indicates how far its beat deviates from the target value after a certain time."

The laser clock will be tested on the International Space Station ISS from 2027 for the use of optical clocks on satellites.