T. Könemann

Bose-Einstein Condensation in Microgravity

Going Down the Tube Two pillars of modern physics are quantum mechanics and general relativity. So far, both have remained apart with no quantum mechanical description of gravity available. Van Zoest et al. (p. 1540; see the Perspective by Nussenzveig and Barata) present work with a macroscopic quantum mechanical system—a Bose-Einstein condensate (BEC) of rubidium atoms in which the cloud of atoms is cooled into a collective quantum state—in microgravity. By dropping the BEC down a 146-meter-long drop chamber and monitoring the expansion of the quantum gas under these microgravity conditions, the authors provide a proof-of-principle demonstration of a technique that can probe the boundary of quantum mechanics and general relativity and perhaps offer the opportunity to reconcile the two experimentally. Studies of atomic quantum states in free-fall conditions may provide ways to test predictions of general relativity. Albert Einstein’s insight that it is impossible to distinguish a local experiment in a “freely falling elevator” from one in free space led to the development of the theory of general relativity. The wave nature of matter manifests itself in a striking way in Bose-Einstein condensates, where millions of atoms lose their identity and can be described by a single macroscopic wave function. We combine these two topics and report the preparation and observation of a Bose-Einstein condensate during free fall in a 146-meter-tall evacuated drop tower. During the expansion over 1 second, the atoms form a giant coherent matter wave that is delocalized on a millimeter scale, which represents a promising source for matter-wave interferometry to test the universality of free fall with quantum matter.

The Space Atom Interferometer project: status and prospects

This paper presents the current status and future prospects of the Space Atom Interferometer project (SAI), funded by the European Space Agency. Atom interferometry provides extremely sensitive and accurate tools for the measurement of inertial forces. Operation of atom interferometers in microgravity is expected to enhance the performance of such sensors. Main goal of SAI is to demonstrate the possibility of placing atom interferometers in space. The resulting drop-tower compatible atom interferometry acceleration sensor prototype is described. Expected performance limits and potential scientific applications in a micro-gravity environment are also discussed.

Realization of a magneto-optical trap in microgravity

We report on the first realization of magneto-optically cooled atoms in microgravity as a first result of the collaboration project ATKAT (atom catapult). We present the compact and robust setup for cooling and trapping neutral 87Rb atoms in microgravity conditions in the drop tower in Bremen⊥ and discuss the specific requirements the setup has to meet. In particular we present a small size and mechanically stable laser system and discuss the specifics of the ultra high vacuum chamber. A free falling magneto-optical trap (MOT) as realized in this project provides a basis for further experiments which aim at investigating cold quantum matter in microgravity. ⊥www.zarm.uni-bremen.de

RUBIDIUM BOSE–EINSTEIN CONDENSATE UNDER MICROGRAVITY

Weightlessness promises to substantially extend the science of quantum gases toward presently inaccessible regimes of low temperatures, macroscopic dimensions of coherent matter waves, and enhanced duration of unperturbed evolution. With the long-term goal of studying cold quantum gases on a space platform, we currently focus on the implementation of an 87Rb Bose–Einstein condensate (BEC) experiment under microgravity conditions at the ZARM drop tower in Bremen (Germany). Special challenges in the construction of the experimental setup are posed by a low volume of the drop capsule (< 1 m3) as well as critical vibrations during capsule release and peak decelerations of up to 50 g during recapture at the bottom of the tower. All mechanical and electronic components have thus been designed with stringent demands on miniaturization, mechanical stability and reliability. Additionally, the system provides extensive remote control capabilities as it is not manually accessible in the tower two hours before and during the drop. We present the robust system and show results from first tests at the drop tower.

ATOMIC QUANTUM SENSORS IN SPACE

In this article we present actual projects concerning high resolution measurements developed for future space missions based on ultracold atoms at the Institut fur Quantenoptik (IQ) of the University of Hannover. This work involves the realization of a Bose–Einstein condensate in a microgravitational environment and of an inertial atomic quantum sensor.

Developments toward atomic quantum sensors

In this proceeding we present ongoing projects concerning high resolution measurements developed for future space missions based on ultracold atoms at the Institut fur Quantenoptik (IQ) of the Leibniz-Universitat Hannover. This work involves the realization of a Bose Einstein condensate in microgravitational environment and an inertial atomic quantum sensor.

Degenerate Bose-Fermi gases in microgravity

Bose Einstein Condensates (BEC) opened the way for realization of atomic ensembles with Heisenberg limited uncertainty. In microgravity extremely dilute samples of BEC can be obtained and observed after a free evolution on timescales of seconds. Applications range from atom optics to matter wave interferometry. This has led us to realize a BEC of 10000 87Rb atoms in microgravity. The experimental results (to be published) establish the fact, that in a microgravity environment ultra-large condensates (≈1.5 mm) after a free evolution of 1 second can be observed. In particular, microgravity provides mass independent confining potential which is very important for the research on a mixture of quantum gases.We aim to realize a new setup for multispecies experiments, which can be used in catapult mode doubling the time for microgravity to 9 seconds. The experiment is planned to use 87Rb and 40K as degenerate Bose and Fermi gases respectively and can be used to carry out experiments on interferometry, Bose-Fermi mixtures and tests of the weak equivalence principle in quantum domain. Up to date progress and future prospects of this ambitious and technically challenging project will be presented.

QUANTUS - degenerate quantum gases in microgravity

Magneto-optically trapped (in a mirror-MOT) 87Rb atoms have been observed in microgravity during the 4.5 s. flight. Furthermore, the experiment was able to capture 3ldr106 atoms at the temperature of 40 muK in an Ioffe-Pritchard magnetic chip trap. The corresponding phase-space density is of the order of 10-7. Evaporative cooling - the final stage on the way towards BEC - is currently being implemented.

BEC in microgravity

Technical realisation of a compact, robust and mobile experiment for the creation of a BEC, which can withstand high forces in a droptower is presented. The compact setup is realised by an atom-chip and a robust DFB-diode laser system.