Millimeter-sized "giant atom" produced

Experiment: quantum system can also reach millimeter size

Interior view of the drop tower in Bremen with a typical throw-off capsule. © ZARM - University of Bremen
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The strange laws of quantum physics, such as the fact that matter behaves much like a wave of light, are valid in the invisible microcosm of atoms and molecules. That a quantum system can also reach millimeter size has now been proven by a consortium of physicists in a pioneering experiment at the Bremen Drop Tower.

Similar experiments with free-falling quantum systems could test Einstein's theory of relativity or lead to super-precision sensors, the scientists around Ernst Rasel from the University of Hannover and Reinhold Walser from the Technical University (TU) Darmstadt report in the research magazine "Science".

Bose-Einstein condensate in the sights

It is always impressive when the applause of thousands of concertgoers turns from a chaotic murmur of noise into a rhythmic collective clap. The same thing happens when physicists from several million atoms produce a so-called Bose-Einstein condensate, or BEC for short. To cause such a phase transition, researchers cool down a cloud of atoms almost down to the absolute temperature zero (-273 ° C).

Atom as matter wave

According to quantum physics, every atom represents a matter wave. As the temperature drops, these matter waves continue to expand until eventually they overlap each other. Similar to ocean waves, which mutually reinforce each other into a giant wave, the millions of individual matter waves then become one big matter wave, the Bose-Einstein condensate. As the BEC follows the laws of quantum physics, it is often called the "giant atom."

Albert Einstein and the Indian physicist Satyendranath Bose predicted the existence of BECs as early as 1924, and they have been manufactured in the laboratory since 1995. An important further step, namely the creation of a BEC in weightlessness, to which physicists attach great hopes, is now a researcher Team succeeded. display

The scientists, whose project is called "Quantus", with the support of the German Aerospace Center (DLR), built the entire BEC generation and detection equipment, which normally fills an entire laboratory, into a man-sized metal capsule and dropped them 120 meters deep from the Fallturm Bremen.

Aerial view of the 146 meter high drop tower on the grounds of the University of Bremen. ZARM - University of Bremen

Free fall for five seconds

During the almost five-second free fall, weightlessness prevailed in the capsule. The first few seconds were needed for BEC production. Thereafter, the condensate was released from the magnetic field that held it and expanded to one millimeter in size during the rest of the second to the muted impact of weightlessness, the researchers said using a CCD Camera in the capsule. In the laboratory, a released BEC can not grow to such a size, as it usually has only a few millimeters long fall distance.

"Our Bose-Einstein condensate is the largest produced so far, " says Theoretical Physicist Walser. He created a computer model of the free-falling BEC that simulated its growth in weightlessness. Paulo Nussenzveig and Jo o CA Barata of the University of Sao Paulo write in a commentary in Science that the team's success proves that it is possible to make BECs reliably in space too. In space, the giant atoms could be very useful.

"BECs can be used to build sensors for the position or rotations of satellites that are significantly more precise than today's sensors, " explains Walser. For matter waves of two BECs overlap, similar to laser beams

an interference pattern that is very sensitive to changes in position or rotation.

The larger a BEC, the more accurate the sensors

The larger a BEC, the more precise sensors can be built. According to the researchers, their accuracy could, for example, be useful for Einstein general relativity tests. Weightless BECs in space could also help answer a fundamental physics question. So far, for the very large, planets and stars, as well as the very small, molecules, atoms and elementary particles, there are two separate theories, namely the general relativity theory and quantum physics.

A free-falling macroscopic quantum system is something that connects the two worlds and could therefore contribute to a unified theory, the researchers say.

How big can a BEC become?

"Our goal is to create BECs in space, preferably on the ISS, " says Walser. Until then there are intermediate stages. First, the BEC will be investigated in a ten-second catapult experiment in the Bremen drop tower. Thereafter, the experiment is to be installed in a rocket in which a parabolic flight is to last several minutes of weightlessness.

"So we want to answer the question as to how big a BEC can become, how it can develop and how it can be used as an ultra-precise acceleration and rotation sensor, " says Walser,

(idw - University of Hannover, University of Darmstadt, 18.06.2010 - DLO)