E. Kajari

Universität des Saarlandes, Saarbrücken, Saarland, Germany

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Publications (17)90.39 Total impact

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    ABSTRACT: Atom interferometers covering macroscopic domains of space-time are a spectacular manifestation of the wave nature of matter. Due to their unique coherence properties, Bose-Einstein condensates are ideal sources for an atom interferometer in extended free fall. In this paper we report on the realization of an asymmetric Mach-Zehnder interferometer operated with a Bose-Einstein condensate in microgravity. The resulting interference pattern is similar to the one in the far-field of a double-slit and shows a linear scaling with the time the wave packets expand. We employ delta-kick cooling in order to enhance the signal and extend our atom interferometer. Our experiments demonstrate the high potential of interferometers operated with quantum gases for probing the fundamental concepts of quantum mechanics and general relativity.
    Physical Review Letters 02/2013; 110(9):093602. · 7.73 Impact Factor
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    M Buser, E Kajari, W P Schleich
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    ABSTRACT: The standard model of modern cosmology, which is based on the Friedmann–Lemaître–Robertson–Walker metric, allows the definition of an absolute time. However, there exist (cosmological) models consistent with the theory of general relativity for which such a definition cannot be given since they offer the possibility for time travel. The simplest of these models is the cosmological solution discovered by Kurt Gödel, which describes a homogeneous, rotating universe. Disregarding the paradoxes that come along with the abolishment of causality in such space–times, we are interested in the purely academic question of how an observer would visually perceive the time travel of an object in Gödel's universe. For this purpose, we employ the technique of ray tracing, a standard tool in computer graphics, and visualize various scenarios to bring out the optical effects experienced by an observer located in this universe. In this way, we provide a new perspective on the space–time structure of Gödel's model.
    New Journal of Physics 01/2013; 15(1):013063. · 4.06 Impact Factor
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    ABSTRACT: 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.
    Journal of Physics Conference Series 12/2011; 327(1):012050.
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    ABSTRACT: 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.
    Science 06/2010; 328(5985):1540-3. · 31.20 Impact Factor
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    ABSTRACT: We show that in complete agreement with classical mechanics, the dynamics of any quantum mechanical wave packet in a linear gravitational potential involves the gravitational and the inertial mass only as their ratio. In contrast, the spatial modulation of the corresponding energy wave function is determined by the third root of the product of the two masses. Moreover, the discrete energy spectrum of a particle constrained in its motion by a linear gravitational potential and an infinitely steep wall depends on the inertial as well as the gravitational mass with different fractional powers. This feature might open a new avenue in quantum tests of the universality of free fall.
    Applied Physics B 06/2010; 100(1). · 1.78 Impact Factor
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    ABSTRACT: Atom interferometry represents a quantum leap in the technology for the ultra-precise monitoring of accelerations and rotations and, therefore, for the science that relies on these quantities. These sensors evolved from a new kind of optics based on matter-waves rather than light-waves and might result in an advancement of the fundamental detection limits by several orders of magnitude. This paper describes the current status of the Space Atom Interferometer project (SAI), funded by the European Space Agency. In a multi-pronged approach, SAI aims to investigate both experimentally and theoretically the various aspects of placing atom interferometers in space: the equipment needs, the realistically expected performance limits and potential scientific applications in a micro-gravity environment considering all aspects of quantum, relativistic and metrological sciences. A drop-tower compatible atom interferometry acceleration sensor prototype has been designed, and the manufacturing of its subsystems has been started. A compact modular laser system for cooling and trapping rubidium atoms has been assembled. A compact Raman laser module, featuring outstandingly low phase noise, has been realized. Possible schemes to implement coherent atomic sources in the atom interferometer have been experimentally demonstrated. KeywordsAtom interferometry-Inertial sensors
    Microgravity - Science and Technology 03/2010; 22(4):551-561. · 0.59 Impact Factor
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    ABSTRACT: 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.
    Science 01/2010; 328(2010):1540-1543. · 31.03 Impact Factor
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    ABSTRACT: Summary form only given. 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 (Icircosl.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 <sup>87</sup>Rb and <sup>40</sup>K 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.
    Lasers and Electro-Optics 2009 and the European Quantum Electronics Conference. CLEO Europe - EQEC 2009. European Conference on; 07/2009
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    ABSTRACT: We compare and contrast the different points of view of rotation in general relativity, put forward by Mach, Thirring and Lense, and Goedel. Our analysis relies on two tools: (i) the Sagnac effect which allows us to measure rotations of a coordinate system or induced by the curvature of spacetime, and (ii) computer visualizations which bring out the alien features of the Goedel Universe. In order to keep the paper self-contained, we summarize in several appendices crucial ingredients of the mathematical tools used in general relativity. In this way, our lecture notes should be accessible to researchers familiar with the basic elements of tensor calculus and general relativity.
    05/2009;
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    ABSTRACT: We experimentally demonstrate the possibility of preparing ultracold atoms in the environment of weightlessness at the earth-bound short-term microgravity laboratory Drop Tower Bremen, a facility of ZARM – University of Bremen. Our approach is based on a freely falling magneto-optical trap (MOT) drop tower experiment performed within the ATKAT collaboration (“Atom-Catapult”) as a preliminary part of the QUANTUS pilot project (“Quantum Systems in Weightlessness”) pursuing a Bose–Einstein condensate (BEC) in microgravity at the drop tower [1, 2]. Furthermore we give a complete account of the specific drop tower requirements to realize a compact and robust setup for trapping and cooling neutral rubidium 87Rb atoms in microgravity conditions. We also present the results of the first realized freely falling MOT and further accomplished experiments during several drops. The goal of the preliminary ATKAT pilot project is to initiate a basis for extended atom-optical experiments which aim at realizing, observing and investigating ultracold quantum matter in microgravity.
    Applied Physics B 01/2007; 89(4):431-438. · 1.78 Impact Factor
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    ABSTRACT: 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 Rb 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
    Journal of Modern Optics 01/2007; 54:2513-2522. · 1.16 Impact Factor
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    ABSTRACT: We describe the non-relativistic time evolution of an ultra-cold degenerate quantum gas (bosons/fermions) falling in Earth's gravity during long times (10 sec) and over large distances (100 m). This models a drop tower experiment that is currently performed by the QUANTUS collaboration at ZARM (Bremen, Germany). Starting from the classical mechanics of the drop capsule and a single particle trapped within, we develop the quantum field theoretical description for this experimental situation in an inertial frame, the corotating frame of the Earth, as well as the comoving frame of the drop capsule. Suitable transformations eliminate non-inertial forces, provided all external potentials (trap, gravity) can be approximated with a second order Taylor expansion around the instantaneous trap center. This is an excellent assumption and the harmonic potential theorem applies. As an application, we study the quantum dynamics of a cigar-shaped Bose-Einstein condensate in the Gross-Pitaevskii mean-field approximation. Due to the instantaneous transformation to the rest-frame of the superfluid wave packet, the long-distance drop (100m) can be studied easily on a numerical grid. Comment: 18 pages latex, 5 eps figures, submitted
    Physical Review A 10/2006; · 3.04 Impact Factor
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    ABSTRACT: Targeting the long term goal of a realizing a Bose-Einstein condensate BEC in space several groups within the QUANTUS collaboration 1 currently focus on the implementation of a BEC experiment at the ZARM drop tower in Bremen In this contribution we study an ensemble of freely falling degenerate bosons or fermions confined in a time-dependent harmonic trap 2 with two internal states in the co-rotating frame of the earth It is possible to transform the many-particle Schroedinger equation to the comoving frame of the drop capsule This yields an efficient description of the mesoscopic degenerate quantum gas 3 The QUANTUS project is supported by the DLR DLR 50 WM 0346 1 A Vogel et al Appl Phys B Special Issue Quantum Mechanics for Space to be published 2006 2 J F Dobson Phys Rev Lett 73 2244 1994 3 G Nandi R Walser E Kajari and W P Schleich to be submitted to Phys Rev A 2006
    01/2006;
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    ABSTRACT: The paper is devoted to the Sagnac effect of Gödel’s Universe. Exact expressions for the Sagnac effect are presented. For this purpose, the authors derive a formula for the Sagnac time delay along a circular path in the presence of an arbitrary stationary metric in cylindrical coordinates. This result is applied to the Gödel’s metric for two different experimental situations: First, the light source and the detector are at rest relative to the matter generating the gravitational field. In this case, an expression is formally equivalent to the familiar nonrelativistic Sagnac time delay. Second, the light source and the detector are at rest relative to the matter. Here it is shown that for a special rotation rate of the detector the Sagnac time delay vanishes. The authors propose a formulation of the Sagnac time delay in terms of invariant physical quantities. It turns out that the result is very close to the analogous formula of the Sagnac time delay of a rotating coordinate system in Minkowski spacetime.
    General Relativity and Gravitation 04/2004; 10(10). · 1.90 Impact Factor
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    ABSTRACT: Applications of coherent matter waves are high resolution interferometers for measuring inertial and gravitational forces as well as testing fundamental physics, for which they may serve as a laser like source with mesoscopic quantum features. Out of possible applications, the test of the principle of equivalence in the quantum domain is selected as a target with the highest scientific interest on timescales of a microgravity experiment at the ISS or on a free flyer (ATV, FOTON or other satellites). The QUANTUS project demonstrated the technological feasibil-ity of coherent matter waves in microgravity. As a next step, the consortium will prepare and procure a sounding rocket mission to demonstrate technologies for matter wave interferome-try based on the broad experience of former developments with experiments in the droptower. Therefore, the experiment has to withstand strong requirements concerning environmental con-ditions (Temperature, shock, environmental pressure, etc.) and needs to be designed to fit in a 600 l volume (diameter 35 cm, length 160 cm). It is considered as an important step towards the technology required for the ISS and other platforms. These experiments will give further insights on the potential of inertial sensors based on atom interferometers and the technology is for example of interest for applications in earth observation and geodesy. They could replace classical techniques relying on test masses and promise a further improvement in the accuracy of such devices.
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    ABSTRACT: Clouds of ultra-cold atoms and especially Bose–Einstein condensates (BEC) provide a source for coherent matter-waves in numerous earth bound experiments. Analogous to optical interferometry, matter-wave interferometers can be used for precision measurements allowing for a sensitivity orders of magnitude above their optical counterparts. However, in some respects the presence of gravitational forces in the lab limits experimental possibilities. In this article, we report about a compact and robust experiment generating Bose–Einstein condensates in the drop tower facility in Bremen, Germany. We also present the progress of building the succeeding experiment in which a two species atom interferometer will be implemented to test the weak equivalence principle with quantum matter. KeywordsBEC–Atom interferometry–Inertial Sensors–Microgravity–Equivalence principle
    Microgravity - Science and Technology 23(3):287-292. · 0.59 Impact Factor
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    ABSTRACT: In the present paper we follow three major themes: (i)concepts of rotation in general relativity, (ii)effects induced by these generalized rotations, and (iii)their measurement using interferometry. Our journey takes us from the Foucault pendulum via the Sagnac interferometer to manifestations of gravito-magnetism in double binary pulsars and in Gödel’s Universe. Throughout our article we emphasize the emerging role of matter wave interferometry based on cold atoms or Bose–Einstein condensates leading to superior inertial sensors. In particular, we advertise recent activities directed towards the operation of a coherent matter wave interferometer in an extended free fall.
    Space Science Reviews 148(1):123-147. · 5.52 Impact Factor

Publication Stats

98 Citations
90.39 Total Impact Points

Institutions

  • 2011
    • Universität des Saarlandes
      • Physikalische und Theoretische Chemie
      Saarbrücken, Saarland, Germany
  • 2010
    • Leibniz Universität Hannover
      • Institute of Quantum Optics
      Hanover, Lower Saxony, Germany
  • 2004–2010
    • Universität Ulm
      • Institute of Quantum Physics
      Ulm, Baden-Württemberg, Germany