Precision Earth observation, single-atom clock goals for new QUEST institute

Scientists at the new Quantum Engineering and Space-Time (QUEST) Research Institute at the Physikalisch-Technische Bundesanstalt (PTB, Braunschweig, Germany) are working on "unimaginably precise" measurement methods for Earth observation, and development of the best atomic clock in the world made of a single aluminum atom—among other challenges.

Prof. Dr. Piet O. Schmidt, Head of the Institute, specializes in new methods of spectroscopy. "We use, for example, the exactly identical frequency distances of the spectral lines in an optical frequency comb in order to investigate atomic or molecular systems", explains Schmidt. "What is also very interesting are the methods of quantum logic originally developed for future quantum computers with stored ions, but which can also be used for investigating special classes of atoms or molecules which were not spectroscopically accessible or could only be accessed with difficulty previously."

He also wants to use the quantum logic spectroscopy to develop an optical atomic clock on the basis of an extremely narrow transition in a single aluminum ion. "There is a chance that it might become the best atomic clock in the world", says Schmidt.

The clock that Schmidt has in mind is to attain a relative uncertainly of 10^-18 (to date the limit at PTB lies at 10^-15, held by the so-called caesium fountain clocks). The researchers will, thus, be able to pursue more intensively the question of whether the fine-structure constant, the gravitational constant or the mass ratio between the electron and the proton, change in space or time, as predicted by some modern theories in physics such as the String Theory. But concrete measurement capabilities will also be connected to this. "The availability of such sensitive clocks will lead to other highly sensitive measuring instruments, which will be able to determine, for example, a change in the gravitational potential of the Earth with an accuracy corresponding to a height difference of one centimeter", explains Schmidt. "Currently the geoid of the Earth is known with an uncertainty of 30 cm to 50 cm." QUEST encourages interdisciplinary cooperation—among engineers who develop of navigation systems, geodesists, and researchers in laser cooled atoms—to enable the development of novel sensors for geoscience and navigation.

QUEST is the name of a whole Excellence Cluster to which the new institute belongs. It is already a prime example of good cooperation among diverse but complementary partners: Next to PTB as the state research institute of the Federal Ministry of Economics (BMWi) with its special knowledge in the field of metrology, i.e. precise measurement technologies, there are six institutes from the Leibniz University of Hannover, the Laser Zentrum Hannover, the German-British Gravitational Wave Detector GEO600 in Ruthe, the Center of Applied Space Technology and Microgravity (ZARM) in Bremen and the Albert Einstein Institute (Max Planck Institute for Gravitational Physics). Now strengthened by the addition of PTB's new QUEST Institute, the joint research is not only to answer the deep fundamental issues of physics, but also to lead to new high-tech products with industry. In its start-up phase the institute is being financed by the German Research Foundation (DFG). After this period of funding, the professorship will be permanently continued by PTB and German Federal Ministry of Economics and Technology (BMWI).

The QUEST Institute at PTB consists of a Professorship ("Experimental Quantum Metrology"), a Junior Research Group ("Cold Ion Quantum Sensors"), a Research Project ("Sub-hertz Lasers and novel optic resonators") as well as several so-called "Task Groups". The QUEST researchers note that "optics is often described as 'the' key technology of the 21st century."

For more information on PTB, Germany's national metrology institute providing scientific and technical services, see the institute's website.