If you think of passing hours, minutes and seconds when you imagine a clock, you’re not wrong, but not completely right, either. When clocks measure time very accurately, scientists can do much more than just state the time:
- Navigation: Atomic clocks are used in satellite navigation. To locate a person or an object, the running times of the exchanged signals are analyzed. The rule of thumb: The more precisely clocks tick, the more precisely things can be successfully located.
- Measuring the Earth’s gravitational field: Atomic clocks are highly sensitive to their environment. According to Einstein’s theory of relativity, local gravitational forces influence the passage of time and thus the rate of clocks. That is why an atomic clock ticks differently at sea level than on a mountain, for example. Today’s best clocks are already able to perceive altitude differences of just a few centimeters.
- The search for “new physics”: Our world is the way it is because the natural constants are what they are. If the natural constants changed, our world would change too. That leads to a fundamental question: Are the natural constants really constant? As natural constants also play a role in atomic clocks and influence the measure of time, scientists are trying to find out with the help of such clocks whether the natural constants undergo changes.
People who research atomic clocks are aware of the clocks’ fields of application: satellite navigation, geodesy, communication technology or in fundamental research.
Timely: Excited atom (glowing) in an
optical clock
For decades, PTB has been acquiring expertise on the construction and operation of atomic clocks and is among the world’s most famous timekeepers. The fact that PTB provides the national time in Germany is just a small, though important task. The even greater task is developing the clocks of tomorrow. What are known as “optical clocks”, which use frequencies in the visible spectral range rather than in the microwave range, are the definitive step toward the next generation of clocks which work, for example, with single or an ensemble of neutral or charged atoms (ions).
With these optical clocks, the measure of time will be raised to a new level of precision from which all the practical applications which can be expected will greatly benefit – from altitude measurement in geodesy to the synchronization of networks with high-precision frequency standards. For such practical applications, however, the highly sensitive technology which tames the underlying quantum states much be transferred from a well-protected and painstakingly stabilized fundamental research laboratory to the rugged environment of practical applications, for example, to the free field in geodesy (PTB’s Sr lattice clock is already used there) or for use as a frequency standard in a server room. For this purpose, the first (and still the only) user-friendly, robust and near-commercial optical clock has been realized at PTB in the “opticlock” project in a consortium with partners from industry and academia.