QUANTUS - bose-einstein condensates in microgravity

introduction

The QUANTUS project („Quantengase unter Schwerelosigkeit“) is a collaboration of nine research groups (established in 2004) with the aim to establish ultracold atoms as high precision quantum sensors in microgravity. To this end, a drop tower proof 87Rb-based Bose-Einstein condensation experiment was set up to demonstrate the feasability of quantum optical experiments in such an environment. In November 2007, the first BEC in microgravity was created, and has since then be examined thoroughly.

Since the first realization of a Bose-Einstein condensate (BEC) in 1995, the research on cold atoms has proceeded at an unprecedented pace. Degenerate quantum gases (BECs as well as Bose-Fermi mixtures) have been found to be a perfect tool to examine phenomena ranging from solid state to gravitational physics.

At extremely low energy scales the wave nature of atoms becomes accessible. In a BEC, each atom occupies the same state. Thus, the whole ensemble can be described by a single, macroscopic wave function. This coherent matter wave can be used as a so-called “atom laser”, i.e. as the matter equivalent to the optical laser. Using standing light waves as diffraction gratings, it is possible to build matter wave interferometers, which can be used to measure inertial forces with a precision inaccessible to classical sensors.

The QUANTUS apparatus is intended as a pathfinder on the way to bringing quantum sensors into space. So far, we have successfully demonstrated the feasability of quantum optical experiments in a microgravity environment. Currently, we are working on the implementation of a matter wave interferometer based on Bragg diffraction into our apparatus.

The setup

Figure 1: The QUANTUS drop capsule in the lab. (Click to enlarge)

Our whole experiment has to fit inside a drop capsule and be fully remote controllable. This means not only rather high constraints on size and weight, but also on power consumption. To meet these requirements, a lot of the used components were self-developed by the project partners.

We use a mirror MOT setup with an atom chip doubling as a mirror. The atom chip provides the strong magnetic fields needed for evaporative cooling of the atoms. The laser system consists of an optically stabilized master laser and two offset locked lasers for cooling and repumping.

A cloud of roughly 1.5 · 107 atoms is collected in the MOT and cooled in an optical molasses to about 10 µK. The remaining atoms are then transferred to a magnetic trap on the atom chip. Via rf-induced evaporation, the ensemble is cooled further until the phase transition occurs. The evaporation takes about 1.3 s and results in a BEC of typically 10 000 atoms.

Acknowledgement

The QUANTUS project is a collaboration of LU Hannover, HU Berlin, U Hamburg, U Ulm, TU Darmstadthttp://www.fbh-berlin.de/and ZARM at U Bremen. It is supported by the German Space Agency DLR with funds provided by the Federal Ministry for Economic Affairs and Energy (BMWi) under grant number 50WM1135.

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