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The nucleus of thorium-229 possesses a property that is unique among all known nuclides: It should be possible to excite it with ultraviolet light. To date, little has been known about the low-energy state of the Th-229 nucleus that is responsible for this property. Together with their colleagues from Munich and Mainz, researchers at the Physikalisch-Technische Bundesanstalt (PTB) have now...

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The Physikalisch-Technische Bundesanstalt (PTB) is known for providing time e.g. for radio-controlled clocks. For this purpose, it operates some of the best cesium atomic clocks in the world. At the same time, PTB is already developing various atomic clocks of the next generation. These clocks are no longer based on a microwave transition in cesium, but they rather operate with other atoms that...

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This revolution has been a long time in the making. Behind it are metrologists working in their scientific laboratories, and scientific managers in their decision-making committees. Now the moment is approaching when many of the old quantities (specifically, the definitions behind them) will have to step down to make way for their successors, who are waiting in the wings. The quantities concerned...

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The "atomic second" was the beginning of a revolutionary era: it was born as early as 1955, when the first cesium atomic clock was put into operation. In the fall of 1967, it was included in the International System of Units. This was the beginning of a development which will, in all likelihood, come to an end in the fall of 2018 when the 20th General Conference on Weights and Measures (CGPM)...

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No one had ever come so close to the ideal laser before: theoretically, laser light has only one single color (also frequency or wavelength). In reality, however, there is always a certain linewidth. With a linewidth of only 10 mHz, the laser that researchers from the Physikalisch-Technische Bundesanstalt (PTB) have now developed together with US researchers from JILA, a joint institute of the...

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At present, the kelvin is literally based on no more than water – on the triple point of water, to be more precise. The base unit of temperature is therefore dependent on a material whose properties may vary. But this is about to change: In the fall of 2018, the kelvin, as well as all the other units of the International System of Units (SI), will be redefined to rest on a solid and invariable...

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The universe of physics is experiencing great changes: by 2018, scientists want to place all physical base units on solid, unchangeable foundation in the form of fundamental constants. The units "meter" and "second" were well ahead of schedule; now the kelvin, the kilogram, the mole and the ampere are next in line. The research activities of the Physikalisch-Technische Bundesanstalt (PTB) are...

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In the past few years, optical atomic clocks have made spectacular progress, becoming 100 times more precise than the best caesium clocks. So far, their precision has been available only locally, since frequency transfer via satellite cannot provide sufficient resolution. This has recently changed thanks to a new direct optical connection between France and Germany, established by joint work of...

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Nach fast 130 Jahren wird das internationale Ur-Kilogramm im Herbst 2018 voraussichtlich in den wohlverdienten Ruhestand geschickt. Dann kommt die Welt zu einem metrologischen Gipfeltreffen zusammen, um über die Neudefinition des Kilogramms zu entscheiden. Wie der Meter und die Sekunde soll künftig auch das Kilogramm über unveränderliche Naturkonstanten definiert werden. Dazu zählen...

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