7th European Graduate College Annual Workshop

Gif-sur-Yvette 30th June - 3rd July 2008

Lectures

Gravitational wave detectors H. Grote Max-Planck-Institute for Gravitational Physics and University of Hannover Callinstr. 38, 30167, Hannover, Germany Tel +49-511-762-2210 E-mail: [email protected] The attempt to directly measure gravitational waves is a rapidly growing business, looking forward to the first detection over the next 0-10 years. After briefly giving some qualitative background on gravitational waves and their possible origins, we will have a glance at the attempts to measure gravitational waves. I will focus then on earth-based laser interferometers, in particular the British-German GEO600 detector [1], to review major measuring principles and associated noise sources disturbing the measurement. We should have time for some outlook to the future of the field then. [1] H. Grote et al, Class. Quantum Grav. 25 114043 (2008).

Anderson localization in ultracold atomic gases L. Sanchez-Palencia Laboratoire Charles Fabry de l’Institut d’Optique, CNRS and Université Paris-Sud, Campus Polytechnique, RD 128, F-91127 Palaiseau cedex, France E-mail: [email protected] In this lecture, I shall give a tutorial introduction to Anderson localization of quantum particles in disordered structures I shall particularly emphasize the required conditions for localization to occur and the characteristics features. Then, I shall review recent progress on disordered Bose-Einstein and discuss perspectives.

Talks

Direct observation of Anderson localization of matter-waves in a controlled disorder J. Billy, V. Josse, Z. Zuo, A. Bernard, B. Hambrecht, P. Lugan, D. Clément, L. Sanchez-Palencia, P. Bouyer, & A. Aspect Laboratoire Charles Fabry de l’Institut d’Optique, CNRS and Université Paris-Sud, Campus Polytechnique, RD 128, F-91127 Palaiseau cedex, France E-mail: [email protected] Predicted in 1958 by P. W. Anderson for electronic wave and latter recognized as a ubiquitous phenomenon in wave physics (as it originates from the interference between multiple scattering paths), the Anderson localization effect has prompted an intense experimental and theoretical activity. To date such exponential localization effect has been already reported in light waves [1, 2, 3, 4] microwaves [5, 6]sound waves [7], and electron gases [8] but there is no direct observation of exponential spatial localization of matter-waves (electrons or others). I will present in this talk the Anderson localization (AL) of a Bose Einstein condensate released into a one-dimensional waveguide in the presence of a controlled disorder created by laser speckle [9] . We image directly the atomic density profiles vs time, and find that weak disorder can lead to the stopping of the expansion and to the formation of a stationary exponentially localized wave function, a direct signature of AL. Moreover we show that, in our one-dimensional speckle potential whose noise spectrum has a high spatial frequency cut-off, exponential localization occurs only when the de Broglie wavelengths of the atoms in the expanding BEC are larger than an effective mobility edge corresponding to that cut-off. In the opposite case, we find that the density profiles decay algebraically, as predicted in ref [10]. The method presented here can be extended to localization of atomic quantum gases in higher dimensions, and with controlled interactions. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]

Wiersma, D.S., Bartolini, P., Lagendijk, A. & Righini R. Nature 390, 671 (1997). Scheffold, F., Lenke, R., Tweer, R. & Maret, G. Nature 398, 206 (1999). Störzer, M., Gross, P., Aegerter, C. M. & Maret, G. Phys. Rev. Lett. 96, 063904 (2006). Schwartz, T., Bartal, G., Fishman, S. & Segev, M. Nature 446, 52 (2007). Dalichaouch, R., Armstrong, J.P., Schultz, S., Platzman, P.M. & McCall, S.L. Nature 354, 53 (1991). Chabanov, A.A., Stoytchev, M. & Genack, A.Z. Nature 404, 850 (2000). Weaver, R.L. Anderson localization of ultrasound. Wave Motion 12, 129 (1990). Akkermans, E. & Montambaux G. Mesoscopic Physics of electrons and photons (Cambridge University Press,2006). Goodman, J.W. Speckle Phenomena in Optics (Roberts compagny publishers, 2007). Sanchez-Palencia, L., Clément, D., Lugan, P., Bouyer, P., Shlyapnikov, G.V. & Aspect, A. Phys. Rev. Lett. 98, 210401 (2007).

Non-reciprocal phase noise in polarisation-maintaining single mode optical fibres F. Steier , R. Fleddermann, G. Heinzel and K. Danzmann Max Planck Institute for Gravitational Physics (Albert-Einstein-Institute, Institute for Gravitational Physics, Leibniz University Hannover Callinstr. 38, 30167, Hannover, Germany Tel +49-511-762-17151, Fax +49-511-762-2781 E-mail: [email protected], https://www.lisa.aei-hannover.de The Laser Interferometer Space Antenna (LISA) is a planned gravitational wave detector in space. It is formed by satellites situated in the corners of an equilateral triangle 5 · 106 km apart from each other. In order to measure the effect of gravitational waves the length change between free floating test masses at the end of the long arms has to be measured with picometer accuracy in the mHz-range. Each satellite has therefore two optical benches – one for each arm. In the current LISA baseline design a fibre link is foreseen to swap part of the laser light between the two optical benches on board each satellite. For this link it is currently planned to use a polarisation maintaining single mode√ optical fibre. Such fibres are known to cause phase noise in the order of up to several rad/ Hz in the mHz frequency range. However, this phase noise can be subtracted from the measurement signal if the observed phase noise of the fibre is reciprocal. For this subtraction to work at the desired√residual noise level, the non-reciprocal phase noise of the fibre needs to be √ below 6 µrad/ Hz, corresponding to non-reciprocal length fluctuations of less than 1 pm/ Hz. Currently there is no data available on the non-reciprocity of optical fibres in the LISA frequency range on this demanding level. We present an overview of experiments conducted in Hanover on the non-reciprocity of such a fibre and their results. The interferometer layout used to measure the non-reciprocity R base plate using the hydroxideis close to the LISA design and is therefore built on a Zerodur catalysis bonding technique. The current status of our experiments and planned future improvements are presented. The focus lies on noise measurements and the characterisation of polarisation effects, back-reflection effects and corrections in the data post-processing.

Grating coupled resonators for laser interferometric gravitational wave detectors M. Britzger , O. Burmeister, D. Friedrich, K. Danzmann and R. Schnabel Max-Planck-Institute for Gravitational Physics, Albert-Einstein-Institute Leibniz Universität Hannover Callinstrasse 38, 30167 Hannover, Germany Tel +49-511-762-17086, Fax +49-511-762-2784 E-mail: [email protected] Traditionally, partly transmissive mirrors are used in interferometers to split and combine coherent optical light fields. For high precision laser interferometers, such as for gravitational wave detection, non-transmissive reflection gratings offer a useful alternative way of splitting and combining. All-reflective components are beneficial because, firstly, they reduce the impact of all thermal issues that are associated with absorbed laser power in optical substrates and, secondly, they allow the use of opaque materials with favourable mechanical and thermal properties. With these two qualities all-reflective interferometer concepts have great potential to become key technologies for enhancing the sensitivity of future generations of laser interferometric gravitational wave detectors. From a functional viewpoint every partly transmissive mirror within an interferometer can be substituted by an appropriate reflection grating because of its analogue input-output phase relations. However, the geometry of the interferometer changes considerably when diffraction gratings are used. In this context, several interferometer concepts based on gratings have been proposed and some of them have been demonstrated experimentally. Based on a so called three-port-grating we present a proof-of-principle experiment for an advanced grating based concept towards the implementation of diffractive optics in future gravitational wave detectors. Therefore we consider a grating as low-loss coupler to FabryPerot cavities. For certain gratings in the resonant case the cavity reflects the laser power towards the laser that hence can be retroreflected towards the cavity by implementing a power recycling mirror. We consider such a three-port-grating coupled double resonator as an alternative to conventional linear three-mirror-cavities as currently used in gravitational wave detectors with arm resonators and power recycling.

Double and negative reflection of cold atoms in non-Abelian gauge potentials 1 ¯ G. Juzeliunas , J. Ruseckas1 , A. Jacob, L. Santos, P. Öhberg2

Institut für Theoretische Physik, Leibniz Universität, Hannover 30167, Germany Website: http://www.itp.uni-hannover.de 1 Institute of Theoretical Physics and Astronomy of Vilnius University, Lithuania 2 School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, UK Atom reflection is studied in the presence of a non-Abelian vector potential proportional to a spin-1/2 operator. 1 ~ + ~κ~σ⊥ )2 + V (r) H= (−i~∇ 2M The potential is produced by a relatively simple laser configuration for atoms with a tripod level scheme. This scheme can for instance be implemented using the transition 23 S1 ↔ 23 P0 in 4 He∗ or the transition 5S1/2 (F = 1) ↔ 5P3/2 (F = 0) in 87 Rb. We show that the atomic motion is described by two different dispersion branches with positive or negative chirality.

Figure 1: Three light fields acting on atom in a tripod configuration As a consequence of that, atom reflection shows unusual features, since an incident wave may split into two reflected ones at a barrier, an ordinary specular reflection, and an additional non-specular one. Remarkably, the latter wave can exhibit negative reflection and may become evanescent if the angle of incidence exceeds a critical value. These reflection properties are crucial for future designs in non-Abelian atom optics. reference: Phys. Rev. Lett. 100, 200405 (2008) or arxiv:0801.2056

N body systems dynamic: application at cold collision between atoms and molecules Mehdi Ayouz , Jacques Robert, Olivier Dulieu Laboratoire Aimé Cotton, Université Paris Sud 11 Bât. 505, 91405, Orsay, France Tel +33-1-69352000 E-mail: [email protected], Website: http://www.lac.u-psud.fr Many theoretical approaches are used to represent low energy collisions between molecules and atoms. The most inconvenient choice is the spatial representation of coordinates which give all kinds of arrangements of the system into several subsystems, as atom - molecule pairs or three atoms. The Jacobi and the hyperspherical[1, 2] representations are the most useful in the field of cold collisions, nevertheless with these representations the physical result is not easy to extract. The Eckart[3] coordinates provide with an alternative based in the axes of inertia of the system, an approach developed by the physicist Carl Eckart in his article in 1934 for N body systems. Our aim is to develop a numerical approach based in these Eckart coordinates in order to represent three body cold collisions. [1] F.T. Smith, J.Math.Phys. 3 735 (1962). [2] R.C. Witen, J.Math.Phys. 9 1103 (1968). [3] C. Eckart, Phys.Rev. 46 383 (1934).

Optimization of GMQDT reference functions for Feshbach resonance characterization R. Osséni , M.Raoult and O.Dulieu Laboratoire Aimé Cotton, Université Paris Sud 11 Bât. 505, 91405, Orsay, France Tel +33-1-69352050 E-mail: [email protected], Website: http://www.lac.u-psud.fr In the past, GMQDT has been used to study dynamical processes such as predissociation or Feshbach resonances [1, 2] in ultracold atomic binary collision. This studies has shown that GMQDT is able to recover Close-Coupling cross sections results and moreover brings more physical insignt on the underlying molecular processes. In this presentation, our purpose is to focus our attention on the analysis of the position and the width of Feshbach resonance in terms of the GMQDT quantities with which the cross section are calculated. Such an analysis has already been undertaken in the treatment of ultra-cold binary atomic collisions, namely in the Wigner threshold law regime. Through this work, we want to advertise that this analysis of the Feshbach resonance characteristics strongly depend on the zero order Hamiltonian used to describe the molecular problem. In the QDT[3, 4, 5] framework, it means that this analysis is completely correlated with the choice of reference functions made in the treatment. In opposition with the Coulomb field problem for which the quantum defects are defined relative to the regular and irregular Coulomb functions, in the present molecular problem, there are an infinite number of possibilities for the choice of the reference functions. It must emphasized that whatever may be this choice, one should obtain the same result for the collision cross-sections as well as for the bound state energies in the discrete range. However, the physical interpretation of these results, as the analysis of the resonance showing up in the cross-section, may be easier according to the choice that has been made. Long time ago, Giusti and Fano and JM Lecomte [6] have implemented a receipe which optimizes this choice of reference functions. [1] [2] [3] [4] [5] [6]

Z. Li and R. V. Krems, Phys. Rev. A 75 032709 (2007). Mies, F. H. and Tiesinga, E. and Julienne, P. S., Phys. Rev. A. 61 022721 (2000). F. S. Ham, Solid St. Phys. 1 127 (1955). M. J. Seaton, Rep. Prog. Phys. 46 167 (1983). M. J. Seaton, Prog. Phys. Soc. 88 801 (1966). J. M. Lecomte, J. Phys. B 20 3645 (1987).

Biological applications of laser fabricated microstructures S. Schlie1,2 , E. Fadeeva1 , J. Koch1 , A. Ngezahayo2 , B. N. Chichkov1 1

Nanotechnology Department, Laser Zentrum Hannover e.V. Hollerithallee 8, 30419 Hannover, Germany Tel. +49-511-7624049, E-mail: [email protected] 2 Institute of Biophysics, Leibniz University, Herrenhaeuser Str. 2, 30419 Hannover, Germany Introduction In the field of biomedicine and tissue engineering the conventional biomaterial surfaces often do not have all desired properties for in vivo applications. Therfore, functionalization methods enabling control over cell behaviour on implant surface are matter of increasing interest. One approach is the use of surface topographies as they affect cell morphology, orientation, adhesion and proliferation [1]. To generate surface structures laser processing is a promising technology in aspects of low surface contamination, controllable surface texturing with a complicated geometry, and low mechanical damage [2, 3]. Moreover, ultrashort laser pulses of femtosecond lasers allow a higher precision, reduced heat-affected zones and a larger variety of surface structures [4, 5]. Material and methods In this work we fabricated silicon (Si) spike structures on singlecrystal p-type silicon (110) wafers by an amplified Ti:Sapphire femtosecond laser system (Femtopower Compact Pro, Femtolasers Produktions GmbH, Austria) which delivers sub30-fs pulses at 800 nm wavelength and a repetition rate of 1 kHz. Negative replicas of these spike structures were produced using silicone elastomer as described in [6]. The wettability of material surfaces was determined by a video-based optical contact angle measuring system (OCA 40 Micro, DataPhysics Instruments GmbH, Germany). To test the influence on cellular behaviour proliferation profiles of fibroblasts and SH-SY5Y neuroblastoma cells were examined. Results The fabricated spike structures showed micrometer dimensions. Surface structuring correlated with an increase of hydrophobic character. Moreover, the structures influenced cellular behaviour. The proliferation of fibroblasts was reduced whereas neuroblastoma cells were not effected. These results indicate a promising technique to functionalize surfaces for biomedical applications as cellular behaviour could be controlled in a cell specific manner. [1] M. J. Dalby, D. Giannaras, M. O. Riehle, N. Gadegaard, S. Affrossman, A. S. G. Curtis Biomaterials 25 77-83 (2004). [2] A. Gaggl, G. Schultes, W.D. Müller, H. Kärcher Biomaterials 21 1067-1073 (2000). [3] G. Petö, A. Karacs, Z. Pászti, L. Guczi, T. Divinyi, A. Joób Appl. Surf. Sci. 186 7-13 (2002). [4] B.N. Chichkov, C. Momma, S. Nolte, F. von Alvensleben, A. Tuennermann Appl. Phys. A 63 109 (1996). [5] J. Koch, F. Korte, T. Bauer, C. Fallnich, A. Ostendorf, B.N. Chichkov Appl. Phys. A 81 325 (2005). [6] C. Reinhardt, S. Passinger, V. Zorba, B.N. Chichkov, C. Fotakis Appl. Phys. A 87 673-677 (2007).

Manipulation of the vibration of cold ground-state molecules Matthieu Viteau,1 Amodsen Chotia,1 Maria Allegrini,1,2 Nadia Bouloufa,1 Olivier Dulieu,1 Daniel Comparat,1 and Pierre Pillet1 1

2

Laboratoire Aimé Cotton, CNRS, Univ Paris-Sud, Bât. 505, 91405 Orsay, France CNISM, Dipartimento di Fisica, Università di Pisa, Largo Pontecorvo 3, 56127 Pisa, Italy

Robust samples of trapped ultracold molecules in their rotational and vibrational ground state are expected to lead to significant advances in molecular spectroscopy, molecular clocks, fundamental test of electron-dipole moment of chirality or of variation of some fundamental constants collision , super or controlled photo-chemistry studies, and perhaps in quantum computation [1, 2]. The difficulty in generalizing laser cooling techniques to molecules has stimulated exploration of alternative approaches to producing ultracold molecules. Methods start with pre-formed molecules usually in the lowest vibrational level, access translational temperature down to a few millikelvins. Until now ultracold molecules, meaning a temperature of the molecular in the micro-or nano-kelvin range, can only be achieved starting with cold atoms. The mecanisms are based on collisional processes: photoassociation, Feshbach magneto-association, three-body collisions, but all these techniques produce a sample of molecules in high vibrational levels. In this talk, I will present our result on the optical pumping and vibrational cooling of molecules, allows us to form a cold ground state molecules sample in the lowest vibrational level (v = 0) [3]. Photoassociation of cold Cs atoms in a distribution of vibrational levels in the ground state (between v = 1 − 10 in X 1 Σ+ g ) is followed by an optical pumping scheme by a shaped femtosecond laser. The broadband character of the femtosecond laser is used to pump the molecules to potentials that efficiently decay to lower vibrational levels and to modify the vibrational distribution. By removing the laser frequencies corresponding to the excitation of the v = 0 level, we realize a dark state for the so-shaped femtosecond laser, yielding with the successive laser pulses to an accumulation of the molecules in the v = 0 level. The validity of this incoherent depopulation pumping method is very general and opens exciting prospects for laser cooling and manipulation of molecules.

[1] J. Doyle, B. Friedrich, R. V. Krems, F. Masnou-Seeuws, Eur. Phys. J. D 31, 149 (2004). [2] R. V. Krems, Int. Rev. Phys. Chem. 24, 99 (2005). [3] M. Viteau, A. Chotia, M. Allegrini, N. Bouloufa, O. Dulieu, D. Comparat, P. Pillet, Science (in press).

Matter wave interferometry with K2 molecules S. Liu1 , I. Sherstov2 , and H. Knöckel1 , Chr. Lisdat2 , E. Tiemann1 1

Institut für Quantenoptik, Leibniz Universität Hannover, D-30167 Hannover, Germany 2 Physikalisch-Technische Bundesanstalt, Bundesallee 100, D-38116 Braunschweig

We operate a matter wave interferometer on a beam of K2 molecules in a Ramsey-Bordé configuration [1]. The two exits of this interferometer, with molecules in either the excited state or the ground state, allow distinct detection schemes for the matter wave interference. While observation of the fluorescence of excited state molecules shows the matter wave interferences superimposed on a complicated incoherent background due to the molecular hyperfine structure, detection of ground state molecules behind the interferometer, exciting them with a fixed frequency laser, gives the interference pattern on a simple symmetric background due to a single hyperfine component. Under certain geometric conditions any of the observed matter wave interferences is composed of two distinct structures, a RamseyBordé interference structure from four laser beams employed as beam splitters for the matter wave, and an additional Ramsey interference structure formed by only two laser beams acting as beam splitters. The higher stability of the Ramsey-Bordé setup due to cancellation of phase drifts and fluctuations in corresponding laser beams promises the Ramsey-Bordé interferometer as a sensitive detector for collisions between molecules and ground state K atoms in the particle beam, when the collisions modify the phase and the damping of the interference pattern. The detection was done by deflecting atoms out of the molecular beam by a resonant laser field, thus switching the experiment between atom-molecule collisions and no collisions. For a better understanding of the Ramsey interferences, we detected the ground state exit in two different distances near the beam splitters and further away downstream of the molecular beam. With active stabilization of the relative phases of the laser beams used as beam splitters the Ramsey interference shows a good phase stability. The better contrast of the Ramsey matter wave interferences as compared to the Ramsey-Bordé setup recommends this method as well suited for further experimental applications. We will introduce between the beam splitters a laser field near resonant to a molecular transition from either the excited state or the ground state to another state. Such experiment allows to determine the transition matrix element of the corresponding molecular transition. By changing the collision characteristics of the K atoms by exciting them to Rydberg states, the collisions between potassium atoms and molecules will be investigated. The present status of the matter wave experiment will be presented. [1] Chr.Lisdat, M.Frank, H.Knöckel, M.-L.Almazor, E.Tiemann, Eur.Phys.J.D 12, 235-240 (2000).

Hollow beams for cold atom manipulation Fabienne DIRY , Michael Mestre, Bruno Viaris de Lesegno, Laurence Pruvost 1 Laboratoire Aimé Cotton Bât 505 Campus d’Orsay 91405 Orsay Cedex Tel: +33169352165 Fax: +33169410156 E-mail: [email protected], Our group examine the possibilities offered by Spatial Light Modulators to create dipole potentials with arbitrary shape in order to apply to cold atoms. As a first experiment we have realised a guide for atoms by shaping the laser beam into a Laguerre-Gaussian mode, creating a sort of tube, empty of light, where the atoms rest confined during their flight in the gravity field. To proceed, we trap Rubidium atoms in a magneto-optical trap and cool them at a temperature of 20 µK. Then we apply the Laguerre-Gaussian beam on atoms. This beam is holographically created by using a Spatial Light Modulators (SLM) as a phase hologram onto a Titanium -Sapphire laser. The SLM is programmed from a computer generated image that we call hologram. For the Laguerre-Gaussian beams, we apply a helicoidal phase hologram on the SLM. These beams are interested because there is not light in the center of the beam so there is not dissipation and heating due to spontaneous emission in the center of the guide. The use of these beams increases the efficiency of the guiding. Moreover, the holograms to create these beams are analytical so the experimental shapes are very close to theoretical ones. In a first time, we have created these beams and applied them to cold atoms. We managed to guide cold atoms and we are studying the efficiency of guiding versus the order of the Laguerre-Gaussian beams and the laser detuning. The technique and the new experimental results concerning the guiding will be presented, and we will discuss future applications of such hollow beams.

Bose Einstein Condensates in shaped optical potentials A. Jaouadi,1,2 M.Telmini,2 and E. Charron1 E-mail: [email protected] Laboratoire de Photophysique Moléculaire du CNRS, Université Paris-Sud, Bâtiment 210, 91405 Orsay Cedex, France. 2 Laboratoire de Spectroscopie Atomique, Moléculaire et Applications, Département de Physique, Faculté des Sciences de Tunis, Université Tunis EL Manar, 2092 Tunis, Tunisia. 1

In this work, we present a realistic theoretical model for generating shaped Bose-Einstein condensates (BECs) of a dilute atomic system, employing blue-detuned Laguerre-Gauss (LG) laser beams. Such laser beams have modes which show a node in the center, and trap the atoms in a cylindrical geometry around the axis of propagation of the beam. We study the effect of changing the azimuthal index of the optical potential generated by these beams. One-dimensional (cigar-shape), two-dimensional (disk-shape) and threedimensional (cylindrical-shape) condensate geometries are explored. We then present an analysis of the BEC growth dynamics, using the quantum kinetic Theory derived by Gardinar et al [1] . Our study shows that, for a fixed volume of the trap, the temperature of condensation increases substantially and the growth duration decreases significantly with the azimuthal index ` of the LG beam. 600

Tc(nK)

500

400

300 0

1

2

3

4

5

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Figure 2: Condensation temperature as a function of the azimuthal index ` in a threedimensional LG potential [1] C.W. Gardiner, M.D. Lee, R.J. Ballagh, M.J. Davis and P. Zoller Phys. Rev. Lett. 81, 5266 (1998).

Quantum Interferometry at the Heisenberg limit with Bose-Einstein Condensates L. Pezzé and A. Smerzi1 Laboratoire Charles Fabry de l’Institut d’Optique Campus Polytechnique, RD 128, Palaiseau cedex, France E-mail: [email protected], 1 BEC-CNR-INFM and Dipartimento di Fisica Universitá di Trento, Povo, Italy E-mail: [email protected] The central goal of interferometry is to estimate phases with the highest possible confidence. On one hand, irreducible fluctuations imposed by the laws of Quantum Mechanics limit the accuracy of a quantum interferometer via the Heisenberg uncertainty principle. On the other hand, quantum entanglement has the potential to revolutionize interferometry by allowing√a phase estimation with sensitivity overcoming the standard quantum (shot-noise) limit, 1/ N and eventually reaching the ultimate bound 1/N , the so-called Heisenberg limit, being N the total number of particles. In this talk, we will discuss tailored states and optimal phase estimation strategies [1, 2] to reach the Heisenberg limit of phase sensitivity with Bose-Einstein Condensates in a MachZehnder interferometer. We also emphasize that the connection between multiparticle-entanglement, spin-squeezing and Heisenberg Limit is well illustrated by the Fisher information [3] which provides a simple measure of the statistical distance among quantum states [4]. [1] L. Pezzé and A. Smerzi, Phys. Rev. A 73 011801 (2006). [2] L. Pezzé, A. Smerzi, G. Khoury, J.F. Hodelin and D. Bouwmeester, Phys. Rev. Lett. 99 223602 (2007); L. Pezzé and A. Smerzi, Phys. Rev. Lett. 100 073601 (2008). [3] L. Pezzé and A. Smerzi, quant-ph/07114840. [4] S.L. Braunstein and C.M. Caves, Phys. Rev. Lett. 72 3934 (1994).

Dipole-dipole interactions in a frozen Rydberg Gas A. Chotia , M. Viteau, T.Vogt, D. Comparat, and P. Pillet Laboratoire Aim´ e Cotton, Bˆ at 505 Campus d’Orsay, 91405 Orsay E-mail: [email protected] Due to their relative important size, Rydberg atoms have large dipole moments. The strong interactions between atoms give rise to the dipole blockade mechanism proposed for realizing fast quantum gates [1]. Attractive and repulsive interactions also offer a possibility to understand the ionization mechanism that leads to a plasma. I will first present the results obtained concerning the dipole blockade mechanism where the strength of the interaction is controlled via an electric field [2, 3]. Then, I will describe the behaviour of a frozen Rydberg gas around a Forster resonance where the attractive or repulsive character of the interaction is clearly shown [4]. Ionization for repulsive potentials is also investigated. [1] [2] [3] [4]

D. Jaksch et al., Phys. Rev. Lett. 85(10):2208-11 (2000). T. Vogt et al., Phys. Rev. Lett. 99(8):083003, (2007). A. Chotia et al., New Journal of Physics (10)045031, (2008). M. Viteau et al., In preparation.

Toward a Stark Decelerator for Rydberg species N. Saquet, J. Beugnon, N. Vanhaecke, P. Pillet Laboratoire Aimé Cotton Bat 505 Campus d’Orsay, 91405, Orsay Cédex, France Tel +331.69.35.20.90 E-mail: [email protected] Website: http://www.lac.u-psud.fr Static electric fields have been used for many years to deflect and focus polar molecules. Time-varying electric fields have been used to change the longitudinal velocity of polar molecules [1]. We are currently building a miniaturized decelerator, in which atoms and molecules excited in an appropriate Rydberg state can be decelerated from a supersonic beam. Such a decelerator should be able to stop Rydberg species within tens of microseconds within a few millimeters [2, 3]. We are using sodium atoms to test and characterize the decelerator. The sodium atoms are ablated from a solid bar into a supersonically expanding gas. We measure a longitudinal temperature on the order of 5K and the tranverse temperature is on the order of 1K. Properties of the supersonic beam such as mean velocity, velocity spreading or intensity change with the carrier gas. We test helium, neon and argon as carrier gases. The sodium atoms are detected by Laser Induced Fluorescence with 589nm radiation at two different places separated by 15cm. The excitation toward the Rydberg state is the next step before testing the deceleration. The full control on both internal and external degrees of freedom is planned with the use of STIRAP processes. Simulations show that sodium atoms excited into the state (n=18, m=2, k=14) and flying initially at 370m/s can be stopped in less than 3 millimeters. This state has a dipolar momentum of 960 Debye under the Inglis-Teller field and experience a force about 1.5 106 g in our decelerator. [1] H. Bethlem, G. Berden and G. Meijer, Phys. Rev. Lett. 83 1558 (1999) [2] N. Vanhaecke, D. Comparat and P. Pillet, J. Phys. B 38 S409 (2005) [3] E. Vliegen and F. Merkt, J. Phys. B 39 L241 (2006)

Time of flight study of H(2s) produced by electron impact on H2 : towards twin atoms A. Medina†∗ , R. Cireasa∗ , Ginette Jalbert† , C. R. Carvalho† , N. V. de Castro Faria† , G. Rahmat∗ and J. Robert∗ ∗

Laboratoire Aimé Cotton, CNRS II, Batiment 505, Campus d’Orsay, 91405 Orsay Cedex, France † Instituto de Física, Universidade Federal do Rio de Janeiro - UFRJ, Caixa Postal 68528, Rio de Janeiro, 21941-972, RJ, Brazil

The purpose of this work is to produce two metastable twin hydrogen atoms from the fragmentation of the hydrogen molecule. The construction of the experimental set up was initiated in the Laboratory Aimé Cotton, University Paris-Sud, in Orsay (France). This experience will be also done at the LaCAM (Laboratory of Atomic and Molecular Collisions), at Federal University of Rio de Janeiro (UFRJ-Brazil). A Campargue supersonic jet provides a colimated molecular beam of H2 which collides with a pulsed electron beam to reach, by Franck-Condon transition, excited states of the molecule. One of these states corresponds to doubly excited ones, which can decay in a pair of correlated atoms in the metastable H(2s) [1] with 40 km/s, opposite speed and spin polarization. The detection of the atoms H(2s) will be performed by registering in coincidence, 25 cm far, the Lyman alpha photons produced by the decay of the 2p states after quenching the 2s-2p states by an electric field [2]. The time of flight spectra of H(2S) can be seen below. In a second stage of the experiment, the entanglement of the twin atoms [3] will be verified by a Stern-Gerlach interferometer according to the procedures described in references [4, 5].

[1] Yulian V. Vanne, Alejandro Saenz, Alex Dalgarno, Robert C. Forrey, Piotr Froelich, Svante Jonsell, Phys. Rev. A 73, 062706 (2006). [2] S. Czuchlewski, S. R. Ryan, and W. H. Wing, Rev. Sci. Instrum. 47, 1026 (1976). [3] U. Fano, Rev. Mod. Phys. 55, 855 (1983). [4] Ch. Miniatura, J. Robert, O. Gorceix, V. Lorent, S. Le Boiteux, J. Reinhardt and J. Baudon, Phys. Rev. Lett. 69, 261 (1992). [5] M. Boustimi, V. Bocvarski, B. Viaris de Lesegno, K. Brodski, F. Perales, J. Baudon and J. Robert; Phys. Rev. A 61, 033602 (2000).

Molecular spectroscopy and the Stark effect of NaK A. Gerdes, H. Knöckel and E. Tiemann Institute of Quantum Optics, Leibniz Universität Hannover Welfengarten 1, 30167 Hannover, Germany Tel +12-34-567890, Fax +09-87-654321 E-mail: [email protected] After spectroscopic measurements with a Fourier-transform spectrometer of NaK in a heatpipe setup [1] and characterization of our new molecular beam apparatus, next steps of the investigation of this molecule are presented. With excitation spectroscopy more information of the the excited electronic state B1 Π has been collected and first dark resonances in a coherent Λ scheme have been observed. The current status will be shown. A homogeneous electric field to be introduced next in the detection zone will modify the rotational structure of the spectral lines under consideration. For a description of the Stark splitting not only the molecular Stark effect of the absolute ground state X1 Σ+ of the molecule, but also that of the excited state B1 Π has to be taken into account. A comparison with theoretical predictions of the dependence of the electric dipole moment function on the vibrational quantum number [2] is possible.

Figure 3: NaK excitation schemes. [1] A. Gerdes et al., submitted to EPJD [2] M. Aymar and O. Dulieu, J. Chem. Phys 122 204302 (2005)

Ultracold dipolar molecules: formation of LiCs and perspectives J. Deiglmayr, A. Grochola, M. Repp, K. Mörtlbauer, C. Glück, R. Wester, and M. Weidemüller Physikalisches Institut Albert-Ludwigs-Universität Freiburg, Germany M. Aymar, O. Dulieu Laboratoire Aimé Cotton, University Paris-Sud XI, Orsay, France Ultracold molecular gases find many applications, reaching from high resolution spectroscopy over tests of the standard model to ultracold chemistry and quantum computing. As an additional specific quality of polar molecules, their permanent electric dipole moment leads to anisotropic, long-range interactions and allows for the precise control of internal and motional degrees of freedom by external electric fields1 . Here we present the photoassociation of ultracold LiCs molecules, stabilized by radiative decay. The molecules are detected using multiphoton ionization spectroscopy with a highresolution time-of-flight mass spectrometer2 . Active photoassociation in an overlapped cesium dark SPOT/lithium MOT, loaded from a single Zeeman-slower, is found to yield a strongly increased production rate compared to photoassociation by the trapping light of a two species MOT3 . We identify photoassociation resonances in the B1 Π potential from a few GHz below the 2S1/2 +6P3/2 asymptote down to several hundred wavenumbers of binding energy. In connection with other experimental data4 this yields a significantly improved value for the ground state dissociation energy. We also investigate ionization spectra of cold LiCs molecules produced via different photoassociation resonances, and find indications for the population of very deeply bound vibrational states in the molecular ground state. Accumulation of these molecules in an optical or electrostatic trap could provide an efficient route for creating large samples of ultracold molecules in the absolute ground state. In preparation for experiments with trapped samples of ultracold dipolar molecules, we have studied scenarios for the alignment of ultracold dipolar molecules based on combinations of static electric fields and strong laser fields5 . For this purpose we calculated the static polarizability tensor for the ground state of all heteronuclear alkalis6 . [1] For a review on polar molecules see J. Doyle, B. Friedrich, R.V. Krems, and F. Masnou-Seeuws, Eur. Phys. J. D 31, 149 (2004) [2] S. D. Kraft, J. Mikosch, P. Staanum, J. Deiglmayr, J. Lange, A. Fioretti, R. Wester, and M. Weidemüller, Appl. Phys. B 89, 453 (2007) [3] S. D. Kraft, P. Staanum, J. Lange, L.Vogel, R. Wester, and M. Weidemüller, J. Phys. B 39, S993 (2006) [4] P. Staanum, A. Pashov, H. Knöckel, and E. Tiemann, Phys. Rev. A 75, 042513 (2007); A. Stein, A. Pashov, P.F. Staanum, H. Knöckel, and E. Tiemann, Eur. Phys. J. D 48, 177 (2008) [5] B. Friedrich et D. Herschbach, J. Phys. Chem. A 103, 10280 (1999) [6] J. Deiglmayr, M. Aymar, and O. Dulieu, submitted to J. Chem. Phys.

Posters

Stark deceleration of SO2 O. Bucicov, E. Tiemann , and Ch. Lisdat1 Institute of Quantum Optics, University of Hannover Welfengarten 1, 30167, Hannover, Germany Tel +49-511-762-2339, Fax 49-511-762-2211 E-mail: [email protected] 1 Physikalisch-Technische Bundesanstalt, Braunschweig We present a Stark decelerator for low-field-seeking states with 326 stages, with which we succeeded in decelerating SO2 molecules to the velocity of about 50 m/s [1]. With this decelerator it should be possible to bring the relatively heavy SO2 molecules to a standstill and to trap them electrostatically. This offers the possibility of studying the predissociation of the trapped cold SO2 at the threshold resulting in the production of cold SO molecules and O atoms. We will measure the velocity distribution of the photofragments. The previous research showed that the dissociation process can be manipulated by an external electric field that shifts the dissociation asymptotes relative to the predissociating levels [2]. In this way the reaction channels can be opened or closed at will or the tuning of the velocity of fragments can be attained, these opportunities being very attractive for the field of cold molecules and cold chemistry. [1] O. Bucicov, Eur. Phys. J. D 46 463 (2008). [2] S. Jung, J. Phys. B 39 S1085 (2006).

State Preparation and Entanglement of Macroscopic Test Masses and the Standard Quantum Limit in Laser Interferometry H. Müller-Ebhardt, H. Rehbein, R. Schnabel, K. Danzmann and Y. Chen Max-Planck-Institut für Gravitationsphysik (Albert-Einstein-Institut) Institut für Gravitationsphysik, Leibniz Universität Hannover Callinstr. 38, 30167 Hannover, Germany E-mail: [email protected] We theoretically show that the preparation of entanglement in position and momentum between two heavily macroscopic mirrors is possible in high-precision laser interferometry [1]. The basis of such a demonstration would be a Michelson interferometer with suspended mirrors and simultaneous homodyne detections at both interferometer output ports. We present the connection between the generation of entanglement and the standard quantum limit (SQL) for a free mass. The SQL is a well-known reference limit in operating interferometers for gravitational-wave detection and provides a measure of when macroscopic entanglement can be observed in the presence of realistic decoherence processes. [1] H. Müller-Ebhardt, H. Rehbein, R. Schnabel, K. Danzmann, Y. Chen, Phys. Rev. Lett. 100 013601 (2008).

A new Experiment for the investigation of ultra-cold Potassium Rubidium Mixtures G. Kleine Büning, J. Will, B. Lücke, S. Drenkelforth, W. Ertmer and J. Arlt Institut für Quantenoptik, Leibniz Universität Hannover Welfengarten 1, 30167, Hannover Tel +49-511-7624882, Fax +49-511-7622211 E-mail: [email protected], Website: http://www.nanokelvin.de/bec In the past few years substantial progress in the field of ultra-cold mixtures has allowed for a novel approach to the field of molecular physics. Especially the use of FeshbachResonances to tune the interactions between atoms in homonuclear as well as in heteronuclear systems opened a large new field of research and enabled experiments which were previously limited by interactions. In Hanover we are planning an experiment which will produce ultra-cold Rubidium and Potassium mixtures and thus provide possibilities for further investigations in the field of cold atomic mixtures. The system is still under construction, the vacuum system is already fully assembled and the lasersystems are in preparation. The setup consists of two glass cells which are spatially separated by a differential pumping stage. In the first glass cell the two species 3D magneto optical trap will be loaded from the background vapour provided by light induced atom desorption from the glass surfaces. The pre-cooled atoms are then moved with a quadrupole trap mounted on a translation stage into a magnetic trap in the second glass cell. This second cell is designed such that the good optical access allows for the implementation of a crossed dipole trap and an optical lattice at a later stage.

Bloch Oscillations of Bose-Einstein Condensates in Disordered Potential Gradients S. Drenkelforth, Georg Kleine Büning, J. Will, W. Ertmer, L. Santos, J.J. Arlt Institut für Quantenoptik, Leibniz Universität Hannover Welfengarten 1, D-30167, Hannover, Germany Tel +49-511-7624882, Fax +49-511-7622211 E-mail: [email protected], Website: http://www.nanokelvin.de/bec We investigate both experimentally and theoretically disorder induced damping of Bloch oscillations of Bose-Einstein condensates in 1D optical lattices. Particles in periodic potentials subjected to an external force will undergo an oscillatory motion instead of a linear acceleration. A comparison with solid state systems, where scattering at imperfections of the crystal structure leads to a strong damping of these Bloch oscillations, gives rise to the question how the controlled addition of disorder to an optical lattice will affect the dynamics of particles in such systems. In our experiments the disorder is realised by a combination of a spatially inhomogeneous optical potential and a magnetic gradient. We show that this inhomogeneous force causes a broadening of the quasimomentum spectrum, which in turn results in a damping of the centre-of-mass oscillation (see Fig. 4). Good quantitative agreement of the experimental damping rates and the simulations using the Gross-Pitaevskii equation is obtained. Our results are relevant for high precision experiments on very small forces, which require the observation of a large number of oscillation cycles. Therefore a detailed quantitative understanding of the effect of the disorder and the underlying mechanism of the damping is important for such applications.

Figure 4: Centre-of-mass position of Bose-Einstein condensates performing damped Bloch oscillations. The disorder depths were 35, 105 and 135 × 10−3 Er , from left to right. A fit to the data (solid red line) and the Gaussian envelope (dashed black line) due to the damping are also shown. [1] [1] S. Drenkelforth et. al., New J. Phys. 10 045027 (2008). [2] T. Schulte et. al., Phys. Rev. A 77 023610 (2008).

Probing Atom-Wall interactions by Quantum Reflection of Bose-Einstein Condensates N. Gaaloul , E.M. Rasel , and W. Ertmer Gottfried Wilhelm Leibniz Universität, Institut für Quantenoptik Welfengarten 1, D - 30167, Hannover, Germany Tel +49 511 762 19192 E-mail: [email protected]. Recently a free expansion of a 10000-Rb atom condensate was achieved for extremely long times (1s)[1]. The Bose-Einstein condensate is first prepared and trapped magnetically in the vicinity of an atom chip. The release of the atomic ensemble is performed when the experiment is dropped down in the ZARM tower facility in Bremen. Thus a free expansion is obtained during the free fall and could be used to observe quantum reflection of the BEC on the chip surface. Several experiments of quantum reflection were done in the last years [2, 3], but our model predicts high reflectivity due to the very slow incident velocities (less than 1 mm/s) of the cold atoms in the Quantus experiment. The dilute character of the cloud after 1s of expansion should also minimize the effect of mean-field interactions and lead to good agreement with the quantum reflection theory. In addition, we aim to interpret theoretically the expected interference fringes between reflected and incoming atoms to obtain a highly accurate measurement of the shift caused by the atom-surface interactions. Thus we could probe the attractive Casimir-Polder potential [4] over an extended spatial range only reached thanks to the coherence of the source and the use of interferometric measurements. [1] [2] [3] [4]

A. Vogel et al., Bose-Einstein Condensates in Microgravity Appl. Phys. B 84 664 (2006). F. Shimizu, Phys. Rev. Lett. 86 987 (2001). T.A. Pasquini et al. , Phys. Rev. Lett. 97 (2006). H.B.G. Casimir, D. Polder Phys. Rev. 73 360 (1948).

Formation of ultracold stable ground state RbCs molecules through photoassociation below the Rb(5s)Cs(6p1/2 ) dissociation limit B. Londoño , J. Mahecha1 , E. Luc-Koenig, A. Crubellier and F. Masnou-Seeuws Laboratoire Aimé Cotton, CNRS II, Bâtiment 505, Campus d’Orsay 91405 Cedex, France. E-mail: [email protected], 1 Instituto de Fìsica, Universidad de Antioquia, Calle 67 No 53-108, AA 1226, Medellìn, Colombia The formation of RbCs molecules through photoassociation of ultracold Rb(5s) and Cs(6s) atoms colling at very low temperature is analyzed theoretically. Molecules are formed in the Rb(5s)Cs(6p) 0+ , 0− and 1 excited electronic state the bellow 5s + 6p1/2 dissociation limit. These unstable molecules decay through spontaneous emission, toward scattering states (pairs of hot atoms) or vibrational states (stable molecules) of the X 1 Σ+ or a3 Σ+ . The Hund’s case c series result from the couplig Hund’s case a states through R dependent spin-orbit interaction [1, 2]. We neglect the rotation of the molecule and its hyperfine structure which cannot be resolved in the experimental multiphoton ionization detection [3]. The Mapped Fourier Grid Hamiltonian method [4] is used to determine the energies and wavefunctions for vibrational and scattering states. The Franck-Condon factors F C(v 0 , v 00 ) for the photoassociation and stabilization processes are systematically calculated as functions of the vibrational quantum numbers in the excited v 0 and ground v 00 states. For the 0+ (P1/2,3/2 ), the resonant character of the spin-orbit coupling gives rise to perturbation in the energy spectra. It also induces an enhancement in the formation of stable molecules and a redistribution of vibrational population in the X 1 Σ+ or a3 Σ+ vibrational states, favouring the formation of deeply bound molecules, as observed in homonuclear Rb2 [5]. Stable molecules are produced mainly in the triplet state with small binding energy (≈ 5cm−1 ) [2]. We show that Raman processes could be finally used for efficiently transferring these excited stable molecules toward the ground vibrational level X 1 Σ+ , v” = 0. [1] H. Fahs, A. R. Allouche, M. Korek, M. Aubert-Frécon. J. Phys. B :At. Mol. Opt. Phys. 35, 1501(2002); M. Marinescu, H. R. Sadehpour, Phys. Rev. A. 59, 390 (1999). [2] T. Bergeman, A. J. Kerman, J. M. Sage, S. Sains, D. DeMille, Eur. Phys. J. D. 31, 179 (2004), and private communication.. [3] A. Fioretti, O. Dulieu and C. Gabbanini J. Phys. B: At. Mol. Opt. Phys. 40, 3283 (2007). [4] V. Kokoouline, O. Dulie, R. Kosloff, F. Masnou-Seeuws. J. Chem. Phy. 110, 9865 (1999); K. Willer, O. Dulie, F. Masnou-Seeuws, J. Chem. Phys. 120, 548 (2004). [5] H. K. Pechkis, D. Wang, Y. Huang, E.E. Eyler, W.C. Stwalley and C. P. Koch Phys. Rev. A 76, 022504 (2007); V. Kokoouline, O. Dulieu, F. Masnou-Seeuws Phys. Rev. A 62, 022504 (2000); C. Amiot, O. Dulieu, J. Vergès Phys. Rev. Lett. 83, 2316 (1999).

Towards low-dimensional and strongly interacting ultracold bosons on atom chip J. Armijo, C. Garrido-Alzar, and I. Bouchoule Laboratoire Charles Fabry de l’Institut d’Optique Campus Polytechnique RD 128, 91127 Palaiseau, France Tel +33-1-64533359, Fax +33-1-64533101 E-mail: [email protected], Website: http://atomoptic.iota.u-psud.fr We use current-carying wires deposited on a chip to magnetically confine and manipulate 87 Rb clouds. In continuation of previous studies that have been done with our apparatus, we are envisioning three experimental schemes in 1D and 2D using a new chip under fabrication. The first project will consist in continuing our group’s study on weakly interacting 1D gases in the typical elongated trap that we create with one wire and a homogeneous bias field [1]. We wish to improve the understanding of the tansition from the decoherent to the quasi-condensate regime. In particular, we wish to clearly identify the intermediate "decoherent quantum regime", where the 1D gas is well described by the ideal Bose gas model, and at the same time highly degenerated. Our idea is to use a quartic (box-like) potential to facilitate the observation of this regime. The second project relies on a technique that has been demonstrated in our group [2]: thanks to rapid modulation of the current in the wires, we are able to smooth the roughness of the wire potentials and bring the atoms very close to the chip, thus realizing strongly confining traps. We will use this technique to observe the Tonks-Girardeau regime for bosons in an elongated 1D Ioffe-Pritchard-like geometry. In this regime, the atoms behave as inpenetrable bosons, which we would like to see by measuring the two-body correlation function. In the third project, we plan to produce a 2D trap using adiabatic dressed potentials, such as demonstrated in [3]. We then want to take benefit from the expertise that our group has developped in precise measurements of density fluctuations and apply it to the study of the Kosterlitz-Thouless transition [4]. In particular, we wish to identify the proliferation of free vortices at the transition as a peak in the density fluctuations. The poster describes the experimental apparatus and presents the implementation and interest of those three research projects. [1] J. Esteve et al., Observation of density fluctuations in an elongated Bose gas: ideal gas and quasicondensate regime Phys. Rev. Lett. 96 130403 (2006). [2] J.B. Trebbia et al., Roughness suppression via rapid current modulation on atom chip, Phys. Rev. Lett. 98 263201 (2007) [3] Y. Colombe et al., Europhys. Lett. 67 593 (2004). [4] Z. Hadzibabic et al., Berezinskii-Kosterlitz-Thouless crossover in a trapped atomic gas, Nature, 441 1118 (2006)

Correlations between atomic pairs. J.-C. Jaskula, A. Perrin, H. Chang, V. Krachmalnicoff, V. Leung, M. Schellekens, D. Boiron, A. Aspect and C. I. Westbrook Laboratoire Charles Fabry, Institut d’Optique Campus Polytechnique, 2 avenue Fresnel, 91127, Palaiseau, France Tel +33 1 64 53 33 29, Fax +33 1 64 53 31 01 E-mail: [email protected] Website: http://atomoptic.iota.u-psud.fr We present the observation of pairs of correlated atoms[1] produced by a collision of two Bose-Einstein condensates of metastable Helium[2]. A Raman transfer is used to divide one condensate into two parts moving in opposite directions with a velocity higher than the sound velocity. The results of that process is the scattering of atoms on a sphere due to the energy and momentum conservation laws. The reconstruction of this sphere with a 3D position-sensitive, single atom detector give access to the distribution of momenta. Thus, we are able to measure a correlation for atoms with opposite momenta but also for atoms scattered in the same direction. This latter effect is known as Hanbury-Brown and Twiss effect. Now that we have a source of correlated atoms, we can imagine measuring the reduction of the noise fluctuations of atom number between two opposite points of the sphere or even giving the proof of the entanglement of these scattered atoms. [1] A. Perrin, H. Chang, V. Krachmalnicoff, M. Schellekens, D. Boiron, A. Aspect and C. I. Westbrook, Observation of atom pairs in spontaneous four-wave mixing of two colliding BoseEinstein condensates , Phys. Rev. Lett. 99 150405 (2007). [2] A. Robert, O. Sirjean, A. Browaeys, J. Poupard, S. Nowak, D. Boiron, C. I. Westbrook and A. Aspect, A Bose-Einstein condensate of metastable atoms, Science 292 461 (2001).

Program