ALEXANDER TSIARAS / SCIENCE PHOTO LIBRARY ALEXANDER TSIARAS / SCIENCE PHOTO LIBRARY
A German physicist looking at a laser beam entering the ion trap chamber of an atomic clock. One of the drawbacks of caesium atomic clocks is the short time that the stream of ions may be viewed, typically 10 milliseconds. The ion trap uses electromagnetic fields to contain hydrogen ions within a small space. The ions may then be observed for periods of up to 10 minutes. The ions oscillate between two energy levels, stimulated by a laser. Counting these oscillations is the key to the incredible accuracy of atomic clocks. Although not as accurate as the American NIST-7 clock, the German team at Hannover expects accuracies of two billionths of a second per day from their clock.
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