Quantum gases in microgravity

Working on this experiment: Jean-Pierre Marburger, Moritz Mihm, Peter Stromberger, André Wenzlawski, Christian Korn, Sören Boles

QUANTUS-Logo-BEC

The QUANTUS (QUANTengase Unter Schwerelosigkeit) project is a DLR-funded joint collaboration between seven German universities (University of Mainz, University of Hanover, Humboldt-University of Berlin, University of Hamburg, University of Bremen, University of Ulm and the Technical University of Darmstadt), the Ferdinand-Braun Institute in Berlin and DLR research institutes in Oberpfaffenhofen, Brunswick and Bremen, aiming for the study of ultra-cold quantum gases in microgravity. Currently we are working on three different experiments within the scope of this project, namely QUANTUS-II, MAIUS, and KALEXUS.

QUANTUS-II

Picture of the QUANTUS-II capsule
Picture of the QUANTUS-II capsule

The QUANTUS-II apparatus is an experiment capable of being operated in the microgravity conditions of the drop tower in Bremen (www.zarm.uni-bremen.de). With this experiment we aim for the generation, manipulation and study of ultra-cold quantum gases of Rubidium and Potassium and mixtures between the two species.

It is the successor of the QUANTUS-I apparatus which was the first experiment to realize a Bose-Einstein condensate in microgravity, observe its free expansion on timescales of seconds and demonstrate the feasibility of Bragg interferometry in microgravity ("Bose-Einstein Condensation in Microgravity", Science 328 (5985), 1540-1543), ("Interferometry with Bose-Einstein Condensates in Microgravity", Phys. Rev. Lett. 110, 093602).

QUANTUS-II will study mixtures of two different atomic species via atom interferometry as a step towards a test of the weak equivalence principle.

Furthermore it is designed to make use of the catapult mode in the drop tower, which launches the payload from the bottom of the tower, effectively doubling the time of microgravity per shot compared to the drop mode QUANTUS-I was operated in. In this mode we were already capable of generating up to four BECs within one catapult shot.

The experiment itself is housed inside the drop tower capsule depicted on the right side. In total it has a height of 980mm and a diameter of 600mm and contains the complete experimental apparatus including laser system, vacuum chamber, electronics, batteries and control computers.

The experiment features a unique 2D+/3D-MOT combination allowing for MOT loading times as short as 150ms and a BEC generation with about 10^5 atoms in 1s (“A high-flux BEC source for mobile atom interferometers“ J. Rudolph et al, 2015 New J. Phys. 17 065001).

Currently the experiment is permanently operated at the drop tower in Bremen and performing drops and catapult shots to demonstrate the required experimental steps towards an atom interferometer with Rubidium. An upgrade of the apparatus to Potassium and atomic mixtures is scheduled for next year.

 

Main Publications:

 

MAIUS

Cad-Design of the MAIUS-1-rocket (top left) as well as the payload (bottom left) and picture of the payload for the MAIUS-1 mission (right)

Within the MAIUS experiment we are taking the next step towards ultra-cold quantum gases in space by demonstrating BEC generation and atom interferometry experiments on sounding rockets.

Lauch of the MAIUS-1 mission

On 23.01.2017 3:30 a.m. MAIUS-1 was successfully launched from the European space and sounding rocket range (Esrange) in northern Sweden, generating the world’s first Bose-Einstein Condensate (BEC) in space and performing the first experiments on atom interferometry with BECs.

During the mission an ensemble of Rubidium-87 atoms was cooled and trapped in a magneto-optical trap, then transferred to a purely magnetic atom chip trap, and in this magnetic trap evaporatively cooled to quantum degeneracy. In the end a Bose-Einstein condensate of several ten thousands of atoms was generated. The list of experiments, which were performed on board the sounding rocket includes studies of the phase transition from a thermal ensemble to a BEC, dynamics in the magnetic trap, internal state preparation, delta kick collimation and also atom interferometry. Even during the boost phase, in which the payload is accelerated by the thrusters, resulting in very high vibration and acceleration levels, atoms could be captured in a magneto-optical trap.

To be able to build such a robust experimental apparatus, a number of different technologies had to be developed in the forefront of this launch.

Our group is mainly focused on the development of the optical systems capable of sustaining the harsh environmental conditions during a rocket flight and at the same time providing the stability and precision required for atom optical experiments. These conditions include the mechanical shocks and vibrations during the launch phase, but also the thermal fluctuations during the rocket flight. Due to the electrical power consumption of the payload, the temperature is expected to rise in the 10°C range during the complete flight.

Picture of a Zerodur-based switching module built for MAIUS
Picture of a Zerodur-based switching module built for MAIUS

To fulfill these requirements, especially with regard to thermal properties we choose to utilize Zerodur as main material for the optical benches.

This glass ceramic made by Schott has the special feature of a vanishing coefficient of thermal expansion over a large temperature range making it a prime choice for space applications in which large temperature variations are to be expected.

As this material is very hard to machine, various jointing techniques have been developed to realize the large spectrum of optical components which is required for a laser system for quantum optical and atom optical applications. These components range from rather simple parts, like mirrors, or beam splitters up to mounting concepts of active components like mechanical shutters or acousto-optical modulators.  The combination of all these components allows the realization of a rich manifold of different modules, like modules for high precision spectroscopy, modules for beam splitting and beam overlapping or modules for beam switching and intensity control, only to name a few.

 

Currently we are setting up the experimental apparatus for the successor missions to MAIUS-1. In MAIUS-2 and MAIUS-3 we will for the first time demonstrate BEC-based dual-species atom interferometry by interrogating BECs of Rubidium and Potassium.

 

Main Publications:

A compact and robust diode laser system for atom interferometry on a sounding rocket”, Schkolnik, V., Hellmig, O., Wenzlawski, A. et al. Appl. Phys. B 122: 217 (2016)

Ultrastable, Zerodur-based optical benches for quantum gas experiments”, H. Duncker et al, Applied Optics 53, 4468 (2014)

"Space-borne frequency comb metrology", M. Lezius et al., Optica 3, 1381-1387 (2016)

 

KALEXUS

KALEXUS team

This DLR-funded project is aiming at the demonstration of the laser technology required to perform experiments with ultra-cold potassium. To this end a laser developed by the Ferdinand-Braun Institute was fiber coupled and connected to a spectroscopy module developed by us. With the help of this spectroscopy module, the laser can be stabilized onto an atomic transition of Potassium. Such a system will be needed for further space missions tackling the study of atomic mixtures between Rubidium and Potassium.

The special challenge of this project, compared to the modules developed within the MAIUS-project, is the low vapor pressure of Potassium which complicates the generation of an absorption signal for the Laser stabilization.

To circumvent this issue, a mechanism to heat the cell, without compromising the thermal insensitivity of the modules, was developed in our group.

Furthermore, a fiber based splitting unit is set up to connect the different functional parts of the system and to provide an offset frequency stabilization.

The KALEXUS mission has flown on the TEXUS 53 multi-user mission, which was launched successfully on 23 January 2016 at 9:30 am (official press release).

 

Main Publications:

"Autonomous frequency stabilization of two extended cavity diode lasers at the potassium wavelength on a sounding rocket", A. N. Dinkelaker et al., Appl. Opt. 56, 1388 (2017)

 

Open Positions

 

Master and bachelor Theses

We offer several interesting topics for Bachelor and master theses.

Potential topics:

- Characterization and optimization of fiberbased optical delivery systems for atom interferometry applications

- Development of test protocols and execution of environmental tests of optical components and systems for their utilization on a sounding rocket

- Design, Development and Characterization of different spectroscopy systems for the frequency stabilization of diode lasers

If you’re interested in one of the topics, just write me an email or stop by for a cup of coffee.

 

Funding

The QUANTUS projects are supported by the German Space Agency DLR with funds provided by the Federal Ministry of Economics and Technology (BMWi) under grant numbers 50 WM 1554 and 50 WP 1433. The KALEXUS project is supported by the German Space Agency DLR with funds provided by the Federal Ministry of Economics and Technology (BMWi) under grant number 50 WM 1345.