MAIUS 2 – ultracold atoms in a space mini-laboratory

Two types of atoms – many experimental and technological challenges

In addition to ultracold rubidium atoms, MAIUS 2 was the first time a sounding rocket flew ultracold potassium atoms. However, the use of two different types of atoms presented a major technological challenge for the team. Generating BECs with two different types of atoms requires twice the number of lasers and therefore more electronics – which means a more complex payload is needed with an almost unchanged mass and volume possible for the apparatus. In addition to the technological challenges, there were also experimental challenges, as the generation of these mixtures is far from trivial. So how can a BEC be created in such a small device?

Atoms in a trap

To create a Bose-Einstein Condensate, the movement of atoms must be dramatically minimised. To do this, the clouds of rubidium and potassium atoms must be cooled to almost minus 273 degrees Celsius – just a fraction of a degree above absolute zero, the coldest temperature possible in the Universe. In a two-stage process, the atoms are first slowed down using miniature lasers – the faster an atom moves, the higher its temperature. Laser pulses slow down the atoms, extracting energy from them. However, this principle of 'laser cooling' can never completely slow them down. This technique alone is not sufficient to bring them close enough to absolute zero.

Energy is simply 'blown away'

Following laser cooling, the second phase of temperature reduction begins in a 'magnetic trap', from which the atoms cannot escape. The trap, an 'atom chip', is a device in which magnetic fields confine and can manipulate cold atoms. The magnetic confinement can be thought of like the trap's 'walls'. The fastest atoms are then selectively removed with the help of microwaves, leaving behind a cloud of atoms that are on average colder than before. This method is comparable to cooling coffee in a cup. If the hot drink is left to stand, it cools relatively slowly. However, if the rising vapour – the remaining energetic gas atoms – is removed by blowing, the hot drink cools down much more quickly.

This evaporative cooling makes it possible to reach temperatures just a breath away from absolute zero – ideal conditions for observing a BEC. The resulting ultracold atoms can then be studied, to understand their ground state – their state of lowest energy – and interactions, and also provide ideal conditions for matter-wave interferometry.

Further experiments will follow with cold atoms and interferometers in space

To achieve previously unattainable accuracy with space-based atomic interferometers, more detailed studies of the dynamics and interactions of Bose-Einstein Condensate mixtures will be important on board future rocket experiments and missions to the ISS or on satellites. BECCAL will then be used to interferometrically compare the fall velocities of BECs from both types of atoms. This will be used to test the part of Einstein's theory of relativity that states that all masses fall at the same rate in a vacuum, known as the equivalence principle. If this hypothesis was to be disproved, the theory of relativity would no longer be fully valid.

Software for research at absolute zero

The DLR Institute for Software Technology, together with the DLR Institute for Satellite Geodesy and Inertial Sensing, provided the software for both the preparation and the execution of the MAIUS-2 cold atom experiments. With the help of specially developed programs, physicists were able to transfer the individual experiment sequences to the onboard computer without in-depth programming knowledge. During the experiment itself, the flight software on the onboard computer was responsible for a variety of tasks. It configured and executed the experiment sequences, collected, stored and transmitted data to ground stations and controlled special hardware components such as cameras during the flight.

No rocket, no research

The Mobile Rocket Base (MORABA) of DLR's Space Operations and Astronaut Training facility was responsible for carrying out the MAIUS-2 launch. In addition to the rocket systems, this also included payload support systems, for example for attitude control during the microgravity phase and recovery at the end of the flight, as well as the rocket's own support systems.

A mission made possible by a German research consortium

The MAIUS-2 project is coordinated by the German Space Agency at DLR with funding from the Federal Ministry for Economic Affairs and Climate Action (BMWK). The MAIUS-2 consortium is led by the University of Bremen. Leibniz University Hannover is the scientific leader in cooperation with Humboldt Universität zu Berlin and the Ferdinand-Braun-Institut in Berlin, the Center of Applied Space Technology and Microgravity (ZARM) at the University of Bremen, Johannes Gutenberg University Mainz, Universität Hamburg, Ulm University and the Technical University of Darmstadt. The research consortium also includes the DLR Institute of Space Systems in Bremen, the DLR Facility for Simulation and Software Technology in Braunschweig, and the DLR Mobile Rocket Base (MORABA), which was responsible for conducting the launch campaign.