Ytterbium Clock at PTB (IMAGE) Physikalisch-Technische Bundesanstalt (PTB) Caption This is the ion trap of the ytterbium clock at PTB. Credit 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.