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PTB produces first Bose-Einstein condensate with calcium atoms

Since 1995, it has been possible to produce Bose-Einstein condensates, by cooling mainly alkali elements close to absolute zero. Completely new possibilities for precision measurements are offered by alkaline earth atoms, as they exhibit very narrow transitions in the optical spectral range. At PTB, it was possible for the first time worldwide to produce a Bose-Einstein condensate from the alkaline earth element calcium

Measured density distribution of the calcium atoms with the spicular Bose-Einstein condensate

If a strongly diluted gas is cooled close to absolute zero, then the quantum-mechanical properties of the gas particles come to the fore. The particles must then be described as waves. If the so-called de Broglie wavelength of the particles is equivalent to the mean particle distance, a special state with new properties emerges: In the case of bosons, i.e. particles with integer spin, a phase transition occurs, in which more and more particles are in the same state. This is called a Bose-Einstein condensate. Since their first generation, Bose-Einstein condensates have been used for manifold investigations into the fundamentals of quantum mechanics, as a model system for solids, or in quantum information technology.

At PTB, it has been possible for the first time worldwide to produce a Bose-Einstein condensate from an alkaline earth element. To this end, 2 · 106 calcium atoms, precooled in magneto-optical traps to a temperature of 20 µK, were loaded in an optical dipole trap. By weakening the holding force, hot atoms evaporate, whereby the remaining atoms are cooled. At a temperature of typically 200 nK, the critical temperature is reached with 105 atoms. Of these, approx. 2 · 104 atoms can be cooled to form a pure condensate.

In contrast to the hitherto customary Bose-Einstein condensates made of alkali elements, alkaline earth elements, such as calcium or also strontium, which are both being investigated at PTB for their suitability as optical clocks, offer with their super narrow spectral lines novel possibilities for precision investigations. Thus, for example, the wave properties could be exploited to construct highly sensitive interferometric sensors for gravitational fields. This goal is now to be further pursued at PTB – among others, as a focus of research of the excellence cluster QUEST (Centre for Quantum Engineering and Space-Time Research) at PTB.

Contact at PTB:

Phone: +49-531-592-0