Quantum object created in space
German researchers have successfully created a cloud of ultracold atoms in space — and begun testing a theory of Albert Einstein’s in the process.
According to Einstein’s Equivalence Principle, all bodies are accelerated at the same rate by the Earth’s gravity, regardless of their properties. Under conditions of microgravity, very long and precise measurements can be carried out to determine whether different types of atoms do indeed fall equally fast.
As part of a national consortium, researchers from Germany’s Ferdinand-Braun-Institut, Leibniz-Institut fuer Hoechstfrequenztechnik (FBH) and Humboldt-Universitaet zu Berlin (HU) set out to test the Equivalence Principle in quantum objects. The MAIUS 1 (Matter-Wave Interferometry in Microgravity) experiment saw the researchers generate a cloud of nano-Kelvin cold rubidium atoms aboard a sounding rocket launched — a cloud which was cooled down with laser light and radiofrequency electrical fields so that the atoms finally formed a single quantum object called a Bose-Einstein condensate (BEC).
To produce a BEC, a cloud of atoms must be cooled down to absolute zero, or -273°C. In a two-phase process, the movement of the atoms must first be decelerated using lasers — because the faster an atom moves, the higher its temperature. After the laser beams slow down the atoms, the particles are then loaded into an atomic trap from which they cannot escape. This trap is created by means of an atom chip on which magnetic fields are generated; the magnetic containment can be thought of as the ‘walls’ of the trap.
After laser cooling, the second phase of the temperature reduction begins in the magnetic trap. During this, the magnetic field is reduced, so that the height of the walls is reduced. Consequently, only the coldest and hence most motionless particles remain in the trap, while the more mobile atoms can surmount the lower barrier.
The parameters of the experiment meant the FBH had to develop hybrid micro-integrated semiconductor laser modules that were suitable for application in space. Additionally, scientists from 11 German research facilities spent several years working to miniaturise the BEC technology to fit into the payload module of a sounding rocket around 2.5 m high and 50 cm in diameter. This was easier said than done, given that such technology normally takes up an entire room!
“Designing a system so compact and robust that it can fly on a sounding rocket has been a major challenge for scientists and engineers,” admitted Stephan Seidel, scientific leader of MAIUS 1 from Leibniz Universität Hannover.
The rocket was finally launched from a facility in northern Sweden on 23 January, with around 100 individual interferometry experiments carried out during the six-minute microgravity phase of the flight. The system was said to work perfectly in space and remains fully operational even after experiencing huge mechanical and thermal stress caused by the rocket launch.
This is just as well for the researchers, as two further missions — MAIUS 2 and 3 — are set to follow in 2018 and 2019. In MAIUS 2, in addition to ultrapure rubidium atoms, ultra-cold potassium atoms will be used on a sounding rocket for the first time. With MAIUS 3, the falling velocity of BEC from both atomic species is to be compared via interferometry. It is this final experiment that will test the Equivalence Principle, which lies at the heart of Einstein’s General Theory of Relativity.
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