QUANTUS-II ― Differential Atom Interferometry in Microgravity

Introduction

The experimental realization of a Bose-Einstein condensate (BEC) in 1995 has opened up a plethora of new possibilities for cold atom research. Today, exciting new phenomena such as quantum phase transitions, superfluidity and matter wave interference are being studied in a multitude of lab-based experiments. The extremely low energies achieved in a typical earth-bound laboratory have motivated us to continue the path towards lower energy scales by overcoming earth-bound laboratory restrictions. This has led us to realize a BEC of 10000⁸⁷Rb atoms in microgravity, during the free fall of the QUANTUS experiment. The experimental results establish the feasibility of cold atom research in microgravity. Ultra-large condensates (~1.5 mm) have been observedafter free evolution times of 1 second, a timescale that is inaccessible in ground-based devices¹.

There are several other advantages of performing an experiment in microgravity or space. In particular, a microgravity environment allows for mass independent confining potentials which are crucial for studies on mixtures of several atomic species such as degenerate Bose-Fermi gases.

In our effort to continuously push the existing frontiers further, we are realizing a new setup which fulfills the criteria of being more compact, having better optical access, higher numbers of atoms, employing multiple atomic species and being able to use the catapult mode of the drop tower, doubling the time of microgravity to 9.4 seconds. The experiment will employ 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 the quantum domain.

¹: van Zoest et al, Science 18 June 2010 Vol. 328 no. 5985, pp. 1540 - 1543

Experimental setup

: Fig.1: Catapult mode drop tower capsule.

The whole setup is housed in a catapult mode drop tower capsule (see Fig.1). The capsule has a total height of 2086mm and a diameter of 814mm. The coloured area shows the payload volume of the capsule which is only 980mm in height times a diameter of 600mm. All necessary components for the experiment, namely the vacuum chamber, the laser system, the electronics, the computer control system and the power supply are fitted into this confined volume.

Another limiting factor is the maximum payload weight of 163,8kg. This is especially challenging since a very good magnetic isolation is needed that will, together with the capsule platforms, already amount to more than half of the permitted weight.

While lightweight materials would consequently be favoured, the apparatus also has to withstand intense forces during launch and impact, that are reaching amplitudes of up to 45g. Consequently all parts of the experiment need to be very rigid to endure a large number of launches without displacement.

Experiment chamber

QUANTUS-II will employ the very first double MOT system in microgravity consisting of a two and a three dimensional magneto optical trap (see Fig.2). With this type of setup the cycle times of the whole experiment can be drastically reduced and the residual pressure in the main experiment chamber will be decreased leading to longer life times of the atomic ensembles.

The highly miniaturized chamber is entirely fabricated out of non-magnetic materials avoiding residual magnetisations, which would lead to unwanted effects disturbing the interferometric measurements. To further reduce parasitic effects of magnetic stray fields two cylindrical mu-metal shields will be wrapped around the experimental setup.

: Fig.2: CAD model of the 2D⁺-MOT and 3D-MOT chamber, separated by a differential pumping stage.

The heart of the experiment chamber is the further optimised atom chip (see Fig.3) built in cooperation with Jakob Reichel. The atom chip setup consists of three layers ranging from mesoscopic structures in the millimeter regime to wires of a thickness of 50µm. With this configuration a fast creation of ultra-cold or degenerate gases will be possible. It also provides the possibility to operate at distances far enough from the chip's surface to permit high precision atom interferometry.

: Fig.3: Atom chip setup during bonding.

Lasersystem

The laser system of QUANTUS-II will be developed in two steps. The first generation system (see Fig.4) is operating the experiment in ground based prestudies, but is also compact and robust enough to withstand the emerging forces of the drop mode of the drop tower. The entire laser system is mounted on a sinlge platform of the capsule with a total heigt of 8 cm and is able to operate the 2D⁺-MOT, the 3D-MOT and provide light for optical pumping, detection and a pair of phase locked laser beams for high precision Raman spectroscopy with rubidium.

: Fig.4 CAD model of the existing laser system mounted entirely on a single platform.

The second generation laser system (see Fig.5) will additionally be able to drive Raman and Bragg transitions for rubidium and potassium. It will be further miniaturized and stable enough to also operate during the catapult start of the drop tower. This laser system is mainly developed and fabricated by our partners at the Humboldt-Universität zu Berlin.

: Fig.5: CAD drawing of the second generation laser platform.

Publications

J.Rudolph et al. - Degenerate Quantum Gases in Microgravity (2010)

Microgravity Sci. Technol. DOI 10.1007/s12217-010-9247-0

	Atom Optics and Quantum Sensors > Quantum Systems in Microgravity > QUANTUS-II
Institut für Quantenoptik Home Profile Education News & Events Atom Optics and Quantum Sensors ATLAS CASI Gyroscope Chip KRb Magnesium MIX Quantum Systems in Microgravity Overview QUANTUS QUANTUS-II MAIUS LASUS Publications Staff Open Positions News Staff Publications Molecules & Lasers Ultrafast Laser Optics Quantum Metrology Applied Laser Physics Molecular Quantum Gases Trapped-Ion Quantum Engineering 508. WE Heraeus-Seminar ICOLS 2011 ICOLS Student Workshop 2011 YAO 2011 iSense Workshop 2012 Leibniz Universität Hannover	QUANTUS-II ― Differential Atom Interferometry in Microgravity Introduction The experimental realization of a Bose-Einstein condensate (BEC) in 1995 has opened up a plethora of new possibilities for cold atom research. Today, exciting new phenomena such as quantum phase transitions, superfluidity and matter wave interference are being studied in a multitude of lab-based experiments. The extremely low energies achieved in a typical earth-bound laboratory have motivated us to continue the path towards lower energy scales by overcoming earth-bound laboratory restrictions. This has led us to realize a BEC of 10000⁸⁷Rb atoms in microgravity, during the free fall of the QUANTUS experiment. The experimental results establish the feasibility of cold atom research in microgravity. Ultra-large condensates (~1.5 mm) have been observedafter free evolution times of 1 second, a timescale that is inaccessible in ground-based devices¹. There are several other advantages of performing an experiment in microgravity or space. In particular, a microgravity environment allows for mass independent confining potentials which are crucial for studies on mixtures of several atomic species such as degenerate Bose-Fermi gases. In our effort to continuously push the existing frontiers further, we are realizing a new setup which fulfills the criteria of being more compact, having better optical access, higher numbers of atoms, employing multiple atomic species and being able to use the catapult mode of the drop tower, doubling the time of microgravity to 9.4 seconds. The experiment will employ 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 the quantum domain. ¹: van Zoest et al, Science 18 June 2010 Vol. 328 no. 5985, pp. 1540 - 1543 Experimental setup Fig.1: Catapult mode drop tower capsule. The whole setup is housed in a catapult mode drop tower capsule (see Fig.1). The capsule has a total height of 2086mm and a diameter of 814mm. The coloured area shows the payload volume of the capsule which is only 980mm in height times a diameter of 600mm. All necessary components for the experiment, namely the vacuum chamber, the laser system, the electronics, the computer control system and the power supply are fitted into this confined volume. Another limiting factor is the maximum payload weight of 163,8kg. This is especially challenging since a very good magnetic isolation is needed that will, together with the capsule platforms, already amount to more than half of the permitted weight. While lightweight materials would consequently be favoured, the apparatus also has to withstand intense forces during launch and impact, that are reaching amplitudes of up to 45g. Consequently all parts of the experiment need to be very rigid to endure a large number of launches without displacement. Experiment chamber QUANTUS-II will employ the very first double MOT system in microgravity consisting of a two and a three dimensional magneto optical trap (see Fig.2). With this type of setup the cycle times of the whole experiment can be drastically reduced and the residual pressure in the main experiment chamber will be decreased leading to longer life times of the atomic ensembles. The highly miniaturized chamber is entirely fabricated out of non-magnetic materials avoiding residual magnetisations, which would lead to unwanted effects disturbing the interferometric measurements. To further reduce parasitic effects of magnetic stray fields two cylindrical mu-metal shields will be wrapped around the experimental setup. Fig.2: CAD model of the 2D⁺-MOT and 3D-MOT chamber, separated by a differential pumping stage. The heart of the experiment chamber is the further optimised atom chip (see Fig.3) built in cooperation with Jakob Reichel. The atom chip setup consists of three layers ranging from mesoscopic structures in the millimeter regime to wires of a thickness of 50µm. With this configuration a fast creation of ultra-cold or degenerate gases will be possible. It also provides the possibility to operate at distances far enough from the chip's surface to permit high precision atom interferometry. Fig.3: Atom chip setup during bonding. Lasersystem The laser system of QUANTUS-II will be developed in two steps. The first generation system (see Fig.4) is operating the experiment in ground based prestudies, but is also compact and robust enough to withstand the emerging forces of the drop mode of the drop tower. The entire laser system is mounted on a sinlge platform of the capsule with a total heigt of 8 cm and is able to operate the 2D⁺-MOT, the 3D-MOT and provide light for optical pumping, detection and a pair of phase locked laser beams for high precision Raman spectroscopy with rubidium. Fig.4 CAD model of the existing laser system mounted entirely on a single platform. The second generation laser system (see Fig.5) will additionally be able to drive Raman and Bragg transitions for rubidium and potassium. It will be further miniaturized and stable enough to also operate during the catapult start of the drop tower. This laser system is mainly developed and fabricated by our partners at the Humboldt-Universität zu Berlin. Fig.5: CAD drawing of the second generation laser platform. Publications J.Rudolph et al. - Degenerate Quantum Gases in Microgravity (2010) Microgravity Sci. Technol. DOI 10.1007/s12217-010-9247-0
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