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Luis Santos - One of the best experts on this subject based on the ideXlab platform.

  • Soliton-soliton scattering in dipolar Bose-Einstein Condensates
    Physical Review A, 2007
    Co-Authors: Rejish Nath, P. Pedri, Luis Santos
    Abstract:

    We analyze the scattering of bright solitons in dipolar Bose-Einstein Condensates placed in unconnected layers. Whereas for short-range interactions unconnected layers are independent, a remarkable consequence of the dipole interaction is the appearance of nonlocal interlayer effects. In particular, we show that both for one- and two-dimensional solitons the interlayer interaction leads to an effective molecular potential between disconnected solitons, which induces a complex scattering physics between them, that includes inelastic fusion into soliton molecules, and strong inelastic resonances. In addition, contrary to the short-range interacting case, a two-dimensional soliton scattering is possible, in which inelastic spiraling occurs, resembling phenomena in photorefractive materials.

  • Bose-Einstein Condensates in optical quasicrystal lattices
    Physical Review A, 2005
    Co-Authors: Laurent Sanchez-palencia, Luis Santos
    Abstract:

    We analyze the physics of Bose-Einstein Condensates confined in two dimensional (2D) quasiperiodic optical lattices, which offer an intermediate situation between ordered and disordered systems. First, we analyze the time-of-flight interference pattern that reveals quasiperiodic long-range order. Second, we demonstrate localization effects associated with quasidisorder as well as quasiperiodic Bloch oscillations associated with the extended nature of the wave function of a Bose-Einstein condensate in an optical quasicrystal. In addition, we discuss in detail the crossover between diffusive and localized regimes when the quasiperiodic potential is switched on, as well as the effects of interaction000.

  • Bose-Einstein Condensates in Optical Quasicrystal Lattices
    Physical Review A, 2005
    Co-Authors: Laurent Sanchez-palencia, Luis Santos
    Abstract:

    We analyze the physics of Bose-Einstein Condensates confined in 2D quasi-periodic optical lattices, which offer an intermediate situation between ordered and disordered systems. First, we analyze the time-of-flight interference pattern that reveals quasi-periodic long-range order. Second, we demonstrate localization effects associated with quasi-disorder as well as quasiperiodic Bloch oscillations associated with the extended nature of the wavefunction of a Bose-Einstein condensate in an optical quasicrystal. In addition, we discuss in detail the crossover between diffusive and localized regimes when the quasi-periodic potential is switched on, as well as the effects of interactions.

  • Phase Fluctuations in Bose-Einstein Condensates
    Applied Physics B - Laser and Optics, 2001
    Co-Authors: D. Hellweg, S. Dettmer, G. V. Shlyapnikov, P. Ryytty, J.j Arlt, W. Ertmer, K. Sengstock, D.s Petrov, H. Kreutzmann, Luis Santos
    Abstract:

    We demonstrate the existence of phase fluctuations in elongated Bose-Einstein Condensates (BECs) and study the dependence of those fluctuations on the system parameters. A strong dependence on temperature, atom number, and trapping geometry is observed. Phase fluctuations directly affect the coherence properties of BECs. In particular, we observe instances where the phase coherence length is significantly smaller than the condensate size. Our method of detecting phase fluctuations is based on their transformation into density modulations after ballistic expansion. An analytic theory describing this transformation is developed.

Patrik Ohberg - One of the best experts on this subject based on the ideXlab platform.

  • Vortex sorter for Bose-Einstein Condensates
    Physical Review A, 2004
    Co-Authors: Graeme Whyte, Patrik Ohberg, John Veitch, Johannes Courtial
    Abstract:

    We have designed interferometers that sort Bose-Einstein Condensates into their vortex components. The Bose-Einstein Condensates in the two arms of the interferometer are rotated with respect to each other through fixed angles; different vortex components then exit the interferometer in different directions. The method we use to rotate the Bose-Einstein Condensates involves asymmetric phase imprinting and is itself new. We have modeled rotation through fixed angles and sorting into vortex components with even and odd values of the topological charge of two-dimensional Bose-Einstein Condensates in a number of states (pure or superposition vortex states for different values of the scattering length). Our scheme may have applications for quantum information processing.

  • Transverse laser modes in Bose-Einstein Condensates
    Physical Review A, 2004
    Co-Authors: Graham Whyte, Patrik Ohberg, Johannes Courtial
    Abstract:

    Bose-Einstein Condensates (BECs) are in many ways similar to laser light. In Fox-Li-type simulations, which involve free evolution of a two-dimensional BEC in combination with periodic focusing and localized loss, we model here numerically the BEC equivalent of transverse aspects of laser resonators. We discuss possible experimental realizations in the form of periodic series of light pulses interacting with the BEC. We show that such experiments can result in trapped, structurally stable, modes analogous to Hermite-Gaussian laser modes. This outlines a new way of trapping BECs and illustrates further the analogy between BECs and laser light.

  • theory of elementary excitations in unstable bose einstein Condensates
    Physical Review A, 2003
    Co-Authors: Ulf Leonhardt, Tamas Kiss, Patrik Ohberg
    Abstract:

    Like classical fluids, quantum gases may suffer from hydrodynamic instabilities. Our paper develops a quantum version of the classical stability analysis in fluids, the Bogoliubov theory of elementary excitations in unstable Bose-Einstein Condensates. In unstable Condensates the excitation modes have complex frequencies. We derive the normalization conditions for unstable modes such that they can serve in a mode decomposition of the noncondensed component. Furthermore, we develop approximative techniques to determine the spectrum and the mode functions. Finally, we apply our theory to sonic horizons - sonic black and white holes. For sonic white holes the spectrum of unstable modes turns out to be intrinsically discrete, whereas black holes may be stable.

  • theory of elementary excitations in unstable bose einstein Condensates
    arXiv: Soft Condensed Matter, 2002
    Co-Authors: Ulf Leonhardt, Tamas Kiss, Patrik Ohberg
    Abstract:

    Like classical fluids, quantum gases may suffer from hydrodynamic instabilities. Our paper develops a quantum version of the classical stability analysis in fluids, the Bogoliubov theory of elementary excitations in unstable Bose-Einstein Condensates. In unstable Condensates the excitation modes have complex frequencies. We derive the normalization conditions for unstable modes such that they can serve in a mode decomposition of the non-condensed component. Furthermore, we develop approximative techniques to determine the spectrum and the mode functions. Finally, we apply our theory to a sonic white hole and find that the spectrum of unstable modes is intrinsically discrete.

Wolfgang Ketterle - One of the best experts on this subject based on the ideXlab platform.

  • Atom optics with Bose-Einstein Condensates: Quantum reflection and interferometry
    Journal of Physics: Conference Series, 2005
    Co-Authors: T.a. Pasquini, G. Jo, Michele Saba, Sebastian Will, Y. Shin-ya, David E Pritchard, Wolfgang Ketterle
    Abstract:

    We present recent results on atom optics with Bose-Einstein Condensates obtained at MIT. These results demonstrate the flexibility of micro-fabricated atom traps (atom-chips) and the interaction of Bose-Einstein Condensates with surfaces through normal incidence quantum reflection. © 2005 IOP Publishing Ltd.

  • transport of bose einstein Condensates with optical tweezers
    Physical Review Letters, 2001
    Co-Authors: T L Gustavson, Aaron E. Leanhardt, Ananth P. Chikkatur, A Gorlitz, Subhadeep Gupta, David E Pritchard, Wolfgang Ketterle
    Abstract:

    We have transported gaseous Bose-Einstein Condensates over distances up to 44 cm. This was accomplished by trapping the condensate in the focus of an infrared laser and translating the location of the laser focus with controlled acceleration. Condensates of order ${10}^{6}$ atoms were moved into an auxiliary chamber and loaded into a magnetic trap formed by a Z-shaped wire. This transport technique avoids the optical and mechanical access constraints of conventional condensate experiments and creates many new scientific opportunities.

  • SPINOR Condensates AND LIGHT SCATTERING FROM Bose-Einstein Condensates
    arXiv: Soft Condensed Matter, 2000
    Co-Authors: Dan M. Stamper-kurn, Wolfgang Ketterle
    Abstract:

    These notes discuss two aspects of the physics of atomic Bose-Einstein Condensates: optical properties and spinor Condensates. The first topic includes light scattering experiments which probe the excitations of a condensate in both the free-particle and phonon regime. At higher light intensity, a new form of superradiance and phase-coherent matter wave amplification were observed. We also discuss properties of spinor Condensates and describe studies of ground-state spin domain structures and dynamical studies which revealed metastable excited states and quantum tunneling.

  • observation of metastable states in spinor bose einstein Condensates
    Physical Review Letters, 1999
    Co-Authors: H. J. Miesner, Ananth P. Chikkatur, Dan Stamperkurn, Jens Stenger, S Inouye, Wolfgang Ketterle
    Abstract:

    Bose-Einstein Condensates have been prepared in long-lived metastable excited states. Two complementary types of metastable states were observed. The first is due to the immiscibility of multiple components in the condensate, and the second to local suppression of spin-relaxation collisions. Relaxation via recondensation of noncondensed atoms, spin relaxation, and quantum tunneling was observed. These experiments were done with F › 1 spinor Bose-Einstein Condensates of sodium confined in an optical dipole trap. [S0031-9007(99)08657-3] PACS numbers: 03.75.Fi, 05.30.Jp, 64.60.My, 67.40.Fd Metastable states of matter, excited states which relax only slowly to the ground state, are commonly encountered. This slow relaxation often arises from the presence of free-energy barriers that prevent a system from directly evolving toward its ground state; if the thermal energy to overcome this barrier is not available, the metastable state may be long lived. Many properties of Bose-Einstein Condensates in dilute atomic gases [1 ‐ 4] arise from metastability; indeed, such Condensates are themselves metastable, since the true equilibrium state is a solid at these low temperatures. Bose-Einstein Condensates in gases with attractive interactions [3] are metastable against collapse due to a kinetic energy barrier [5]. The persistence of rotations in Condensates with repulsive interactions hinges on whether

  • Optically Confined Bose–Einstein Condensates
    Journal of Low Temperature Physics, 1998
    Co-Authors: J. Stenger, Ananth P. Chikkatur, Dan M. Stamper-kurn, H. J. Miesner, M. R. Andrews, Shin Inouye, Wolfgang Ketterle
    Abstract:

    With an optical dipole trap it is possible to confine Bose–Einstein Condensates in different hyperfine states and in arbitrary magnetic bias fields, thus overcoming two major limitations of magnetic traps. In this review paper we characterize the properties of such a dipole trap and we summarize experiments which made use of the new experimental possibilities, including the reversible formation of a Bose–Einstein condensate, the observation of Feshbach resonances in sodium and the ground state properties of spinor Bose-Einstein Condensates. Finally, we present some new results on the shape of magnetically trapped and ballistically expanding Condensates.

Hui Zhai - One of the best experts on this subject based on the ideXlab platform.

  • spin orbit coupled spinor bose einstein Condensates
    Physical Review Letters, 2010
    Co-Authors: Chunji Wang, Chaoming Jian, Hui Zhai
    Abstract:

    An effective spin-orbit coupling can be generated in a cold atom system by engineering atom-light interactions. In this Letter we study spin-1/2 and spin-1 Bose-Einstein Condensates with Rashba spin-orbit coupling, and find that the condensate wave function will develop nontrivial structures. From numerical simulation we have identified two different phases. In one phase the ground state is a single plane wave, and often we find the system splits into domains and an array of vortices plays the role of a domain wall. In this phase, time-reversal symmetry is broken. In the other phase the condensate wave function is a standing wave, and it forms a spin stripe. The transition between them is driven by interactions between bosons. We also provide an analytical understanding of these results and determine the transition point between the two phases.

Masahito Ueda - One of the best experts on this subject based on the ideXlab platform.

  • spinor bose einstein Condensates
    Physics Reports, 2012
    Co-Authors: Yuki Kawaguchi, Masahito Ueda
    Abstract:

    Abstract An overview of the physics of spinor and dipolar Bose–Einstein Condensates (BECs) is given. Mean-field ground states, Bogoliubov spectra, and many-body ground and excited states of spinor BECs are discussed. Properties of spin-polarized dipolar BECs and those of spinor–dipolar BECs are reviewed. Some of the unique features of the vortices in spinor BECs such as fractional vortices and non-Abelian vortices are delineated. The symmetry of the order parameter is classified using group theory, and various topological excitations are investigated based on homotopy theory. Some of the more recent developments in a spinor BEC are discussed.

  • Collision dynamics of non-Abelian vortices in spinor Bose-Einstein Condensates
    Journal of Low Temperature Physics, 2010
    Co-Authors: Michikazu Kobayashi, Yuki Kawaguchi, Muneto Nitta, Masahito Ueda
    Abstract:

    Bose-Einstein Condensates with spin degrees of freedom admit various topological phases and excitations. Non-Abelian vortices offer a remarkable example which is expected to be realized in the cyclic phase of the spin-2 spinor Bose-Einstein Condensates. We demonstrate that the non-Abelian property of non-Abelian vortices shows the unique effect in their collision dynamics, i.e., unlike Abelian vortices, they do neither reconnect themselves nor pass through each other but create a rung vortex between them.

  • VORTICES IN MULTICOMPONENT BOSE–EINSTEIN Condensates
    International Journal of Modern Physics B, 2005
    Co-Authors: Kenichi Kasamatsu, Makoto Tsubota, Masahito Ueda
    Abstract:

    We review the topic of quantized vortices in multicomponent Bose–Einstein Condensates of dilute atomic gases, with an emphasis on the two-component Condensates. First, we review the fundamental structure, stability and dynamics of a single vortex state in a slowly rotating two-component Condensates. To understand recent experimental results, we use the coupled Gross–Pitaevskii equations and the generalized nonlinear sigma model. An axisymmetric vortex state, which was observed by the JILA group, can be regarded as a topologically trivial skyrmion in the pseudospin representation. The internal, coherent coupling between the two components breaks the axisymmetry of the vortex state, resulting in a stable vortex molecule (a meron pair). We also mention unconventional vortex states and monopole excitations in a spin-1 Bose–Einstein condensate. Next, we discuss a rich variety of vortex states realized in rapidly rotating two-component Bose–Einstein Condensates. We introduce a phase diagram with axes of rotatio...