Publications (26)128.51 Total impact

Article: Representationfree description of lightpulse atom interferometry including noninertial effects
[Show abstract] [Hide abstract] ABSTRACT: Lightpulse atom interferometers rely on the wave nature of matter and its manipulation with coherent laser pulses. They are used for precise gravimetry and inertial sensing as well as for accurate measurements of fundamental constants. Reaching higher precision requires longer interferometer times which are naturally encountered in microgravity environments such as droptower facilities, sounding rockets and dedicated satellite missions aiming at fundamental quantum physics in space. In all those cases, it is necessary to consider arbitrary trajectories and varying orientations of the interferometer setup in noninertial frames of reference. Here we provide a versatile representationfree description of atom interferometry entirely based on operator algebra to address this general situation. We show how to analytically determine the phase shift as well as the visibility of interferometers with an arbitrary number of pulses including the effects of local gravitational accelerations, gravity gradients, the rotation of the lasers and noninertial frames of reference. Our method conveniently unifies previous results and facilitates the investigation of novel interferometer geometries. 
Article: Ion chains as quantum reservoirs
[Show abstract] [Hide abstract] ABSTRACT: We characterize ion chains as quantum reservoirs, which can mediate entanglement between two objects coupled with the vibrational modes of the chain. The systems which become entangled are the transverse vibrations of two heavy impurity defects, embedded in the ion chain, which couple with the chain axial modes by means of an external optical potential. General scaling properties are verified for large chains, where we demonstrate that entanglement is a stationary feature and does not depend on the finite size of the physical system. We then analyze the dynamics for small chains, composed by ten to dozens of ions, and propose a measurement scheme, which allows one to verify the existence of the predicted entangled state.  [Show abstract] [Hide abstract] ABSTRACT: Atom interferometers covering macroscopic domains of spacetime are a spectacular manifestation of the wave nature of matter. Due to their unique coherence properties, BoseEinstein condensates are ideal sources for an atom interferometer in extended free fall. In this paper we report on the realization of an asymmetric MachZehnder interferometer operated with a BoseEinstein condensate in microgravity. The resulting interference pattern is similar to the one in the farfield of a doubleslit and shows a linear scaling with the time the wave packets expand. We employ deltakick 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.

Article: Visualization of the Gödel universe
[Show abstract] [Hide abstract] 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.  [Show abstract] [Hide abstract] ABSTRACT: We theoretically show how two impurity defects in a crystalline structure can be entangled through coupling with the crystal. We demonstrate this with a harmonic chain of trapped ions in which two ions of a different species are embedded. Entanglement is found for sufficiently cold chains and for a certain class of initial, separable states of the defects. It results from the interplay between localized modes which involve the defects and the interposed ions, it is independent of the chain size, and decays slowly with the distance between the impurities. These dynamics can be observed in systems exhibiting spatial order, viable realizations are optical lattices, optomechanical systems, or cavity arrays in circuit QED.
 [Show abstract] [Hide abstract] ABSTRACT: One stumbling block which limits our observation of quantum effects in the macroscopic world is decoherence. For this reason the study of decoherence and dissipation in open quantum systems has attracted a lot of attention. It has been shown that the generation of long distance entanglement is possible between oscillators via a harmonic crystal (Wolf et al, EPL, 95(2011) 60008). The aim of this current work is to propose an experimentally feasible setup to test the possibility of the creation of long distance entanglement. For this purpose we consider an ion chain in a linear Paul trap with two embedded impurities, whose transverse modes resemble the two degrees of freedom that we aim to entangle via the rest of the chain. With the aid of appropriately designed laser fields, the dynamics described in (Wolf et al, EPL, 95(2011) 60008) is reproduced. The resulting entanglement between the transverse modes of the impurities is analysed by means of the logarithmic negativity.
 [Show abstract] [Hide abstract] ABSTRACT: Two defect particles that couple to a harmonic chain, acting as common reservoir, can become entangled even when the two defects do not directly interact and the harmonic chain is effectively a thermal reservoir for each individual defect. This dynamics is encountered for sufficiently low temperatures of the chain and depends on the initial state of the two oscillators. In particular, when each defect is prepared in a squeezed state, entanglement can be found at time scales at which the steady state of a single defect is reached. We provide a microscopic description of the coupled quantum dynamics of chain and defects. By means of numerical simulations, we explore the parameter regimes for which entanglement is found under the specific assumption that both particles couple to the same ion of the chain. This model provides the microscopic setting where bathinduced entanglement can be observed.
 [Show abstract] [Hide abstract] 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 droptower compatible atom interferometry acceleration sensor prototype is described. Expected performance limits and potential scientific applications in a microgravity environment are also discussed.
 [Show abstract] [Hide abstract] ABSTRACT: Clouds of ultracold atoms and especially Bose–Einstein condensates (BEC) provide a source for coherent matterwaves in numerous earth bound experiments. Analogous to optical interferometry, matterwave 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
 [Show abstract] [Hide abstract] ABSTRACT: The generation of entanglement between two oscillators that interact via a common reservoir is theoretically studied. The reservoir is modeled by a onedimensional harmonic crystal initially in thermal equilibrium. Starting from a separable state, the oscillators can become entangled after a transient time, that is of the order of the thermalization time scale. This behavior is observed at finite temperature even when the oscillators are at a distance significantly larger than the crystal's interparticle spacing. The underlying physical mechanisms can be explained by the dynamical properties of the collective variables of the two oscillators which may decouple from or be squeezed by the reservoir. Our predictions can be tested with an ion chain in a linear Paul trap.
 [Show abstract] [Hide abstract] 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 gravitomagnetism 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.
 [Show abstract] [Hide abstract] 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 BoseEinstein 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 BoseEinstein condensate during free fall in a 146metertall 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 matterwave interferometry to test the universality of free fall with quantum matter.
 [Show abstract] [Hide abstract] 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.
 [Show abstract] [Hide abstract] ABSTRACT: Atom interferometry represents a quantum leap in the technology for the ultraprecise 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 matterwaves rather than lightwaves 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 multipronged 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 microgravity environment considering all aspects of quantum, relativistic and metrological sciences. A droptower 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 interferometryInertial sensors
 [Show abstract] [Hide abstract] 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 BoseEinstein 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 BoseEinstein condensate during free fall in a 146metertall 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 matterwave interferometry to test the universality of free fall with quantum matter.

Conference Paper: Degenerate BoseFermi gases in microgravity
[Show abstract] [Hide abstract] 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 ultralarge 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, BoseFermi 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.  [Show abstract] [Hide abstract] 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 selfcontained, 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.
 [Show abstract] [Hide abstract] ABSTRACT: The weak Equivalence Principle (EP) represents a corner stone in the General Theory of relativity [1]. The validity of this postulate was and is currently tested in different groups with different systems. Among this multitude atom interferometry is considered to be one of the most powerful tools in performing highprecision measurements [2]. Using two atom species in free fall with different masses allows comparing two independent measurements of g. This is made possible by creating simultaneously in a single experiment a mixture of two atomic species at a temperature close to the absolute zero. This regime is suitable to the observation of matter waves at long time scales needed for quantum tests. In this letter an overview of the last developments of these quantum sensors is done. The uptodate progress and future prospects in our group of these ambitious and technically challenging projects will be presented as well.

Article: The Drop Tower Bremen as a source for atom optical experiments in gravitationfree conditions
[Show abstract] [Hide abstract] ABSTRACT: Low gravity provides an outstanding basis for precision measurements in atom optics pursuing multidisciplines in fundamental physics. On the other hand it leads to an utilization of ultracold quantum matter techniques in unique practical applications. We report on the first establishments of atom optical experiments in the gravitationfree conditions at the Drop Tower Bremen in Germany, a facility of the Center of Applied Space Technology and Microgravity (ZARM). The chosen drop tower has an easy access to low gravity on earth with a daily usage, a more than sufficient time of free fall for experiments in quantum regimes (about 4s in drop mode and about 9s in catapult mode) and a well quality of weightlessness of 106g. Our report demonstrates the results of the precursor pilot project ATKAT ("atom catapult") and the current pilot project QUANTUS ("quantum systems under weightlesness") . The pure technological experiment ATKAT could successfully realize a compact and robust setup for trapping and cooling neutral rubidium atoms ( 87Rb) in microgravity conditions. After ATKAT's test accomplishment we have started the parallel developed QUANTUS main pilot projekt to investigate quantum degenerated gases in free fall. The first BoseEinstein condensate (BEC) in a weightless environment world wide and longest evolution times of the 87Rb BEC up to 1s could be achieved within the science experiment QUANTUS. In respect thereof our collaboration opens further opportunities in atom optics. At least we will give an outlook of the new QUANTUS II project and its supporting project PRIMUS ("precision interferometry with matter waves under weightlessness") aiming on a precise inertial sensor by using an atom interferometer under weightlessness.  [Show abstract] [Hide abstract] ABSTRACT: We experimentally demonstrate the possibility of preparing ultracold atoms in the environment of weightlessness at the earthbound shortterm microgravity laboratory Drop Tower Bremen, a facility of ZARM – University of Bremen. Our approach is based on a freely falling magnetooptical trap (MOT) drop tower experiment performed within the ATKAT collaboration (“AtomCatapult”) 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 atomoptical experiments which aim at realizing, observing and investigating ultracold quantum matter in microgravity.
Publication Stats
306  Citations  
128.51  Total Impact Points  
Top Journals
Institutions

20042015

Universität Ulm
 Institute of Quantum Physics
Ulm, BadenWürttemberg, Germany


20112014

Universität des Saarlandes
 Physikalische und Theoretische Chemie
Saarbrücken, Saarland, Germany
