Schematic Description of the Experiment (IMAGE) Physikalisch-Technische Bundesanstalt (PTB) Caption A tunable laser excites an extremely narrow-band resonance in an Yb+ ion of an atomic clock. The electron wave function of the ion's excited state is marked in yellow. Two ions with wave functions that are oriented at right angles are interrogated by means of laser light with an adjustable frequency shift to measure a possible frequency difference. The whole experimental setup rotates together with the Earth once a day relative to the fixed stars. Credit Physikalisch-Technische Bundesanstalt (PTB) Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.