Anna Marchant

    Formation of bright solitary matter-waves
    A L Marchant
    PhD Thesis, Durham University (2012)
    This thesis presents the development of an experimental apparatus to produce Bose-Einstein condensates (BECs) with tunable interparticle interactions. The ability to precisely control the strength of these interactions, and even to switch them from repulsive to attractive, allows one to probe novel regimes of condensate physics, from the collapse of attractively interacting BECs and the formation of solitary matter-waves to the observation of beyond mean-field effects in strongly repulsive condensates.

    The construction and characterisation of both a single and crossed beam optical dipole trap is presented. In the single beam case we develop a technique allowing the guided transport of atoms along the beam and up to a roomtemperature surface; a technique which can be used to evaporatively cool the trapped atomic cloud. We produce Bose-Einstein condensates of 87Rb in the F = 1, mF = -1 state in this trap, comparing the effect of beam waist on the evaporation trajectory. In the crossed beam trap Bose-Einstein condensation of 87Rb is realised in three distinct trapping con gurations, along with a 1D optical lattice formed by changing the polarisation of the beams.

    A method of direct cooling of 85Rb atoms in the crossed trap is developed using a magnetic Feshbach resonance to precisely tune both the elastic and inelastic scattering properties of the atoms. The resonance used for this work occurs at 155 G in collisions between atoms in the F = 2, mF = -2 state of 85Rb. Bose-Einstein condensates of up to 40,000 85Rb atoms are formed in this trap and we demonstrate the presence of tunable interatomic interactions, exploring the collapse phenomenon associated with attractive condensates.

    By loading the 85Rb condensate into a quasi-1D waveguide we show that stable attractive condensates can be created, taking the form of bright solitary matter-waves. We observe a solitary wave of 2,000 atoms which propagates, without dispersion, along the waveguide over a distance of 1.1 mm. The particle-like nature of the solitary wave is demonstrated by classical reflection of the wavepacket from a repulsive Gaussian barrier.
    Controlled formation and reflection of a bright solitary matter-wave
    A L Marchant, T P Billam, T P Wiles, M M H Yu, S A Gardiner, S L Cornish
    Nat. Commun. 4, 1865 (2013)
    Solitons are non-dispersive wave solutions that arise in a diverse range of nonlinear systems, stablised by a focussing or defocussing nonlinearity. First observed in shallow water, solitons have subsequently been studied in many other fields including nonlinear optics, biophysics, astrophysics, plasma and particle physics. They are characterised by well localised wavepackets that maintain their initial shape and amplitude for all time, even following collisions with other solitons. Here we report the controlled formation of bright solitary matter-waves, the 3D analog to solitons, from Bose-Einstein condensates of 85Rb and observe their propagation in an optical waveguide. These results pave the way for new experimental studies of bright solitary matterwave dynamics to elucidate the wealth of existing theoretical work and to explore an array of potential applications including novel interferometric devices, the study of short-range atom-surface potentials and the realisation of Schrodingercat states.
    Bright solitary matter waves: formation, stability and interactions
    Contribution to: Spontaneous Symmetry Breaking, Self-trapping, and Josephson Oscillations (Progress in Optical Science and Photonics)
    T P Billam, A L Marchant, S L Cornish, S A Gardiner, N G Parker
    arXiv:1209.0560 (2012)
    In recent years, bright soliton-like structures composed of gaseous Bose-Einstein condensates have been generated at ultracold temperature. The experimental capacity to precisely engineer the nonlinearity and potential landscape experienced by these solitary waves offers an attractive platform for fundamental study of solitonic structures. The presence of three spatial dimensions and trapping implies that these are strictly distinct objects to the true soliton solutions. Working within the zero-temperature mean-field description, we explore the solutions and stability of bright solitary waves, as well as their interactions. Emphasis is placed on elucidating their similarities and differences to the true bright soliton. The rich behaviour introduced in the bright solitary waves includes the collapse instability and symmetry-breaking collisions. We review the experimental formation and observation of bright solitary matter waves to date, and compare to theoretical predictions. Finally we discuss the current state-of-the-art of this area, including beyond-mean-field descriptions, exotic bright solitary waves, and proposals to exploit bright solitary waves in interferometry and as surface probes.
    Bose-Einstein condensation of 85Rb by direct evaporation in an optical dipole trap
    A L Marchant, S Händel, S A Hopkins, T P Wiles and S L Cornish
    Phys. Rev. A 85, 053647 (2012)
    We report a simple method for the creation of Bose-Einstein condensates of 85Rb by direct evaporation in a crossed optical dipole trap. The independent control of the trap frequencies and magnetic bias field afforded by the trapping scheme permits full control of the trapped atomic sample, enabling the collision parameters to be easily manipulated to achieve efficient evaporation in the vicinity of the 155 G Feshbach resonance. We produce nearly pure condensates of up to 4x104 atoms and demonstrate the tunable nature of the atomic interactions.
    Magnetic transport apparatus for the production of ultracold atomic gases in the vicinity of a dielectric surface
    S Händel, A L Marchant, T P Wiles, S A Hopkins S L Cornish
    Rev. Sci. Instrum. 83, 013105 (2012)
    We present an apparatus designed for studies of atom-surface interactions using quantum degenerate gases of 85Rb and 87Rb in the vicinity of a room temperature dielectric surface. The surface to be investigated is a super-polished face of a glass Dove prism mounted in a glass cell under ultra-high vacuum (UHV). To maintain excellent optical access to the region surrounding the surface magnetic transport is used to deliver ultracold atoms from a separate vacuum chamber housing the magneto-optical trap (MOT). We present a detailed description of the vacuum apparatus highlighting the novel design features; a low profile MOT chamber and the inclusion of an obstacle in the transport path. We report the characterization and optimization of the magnetic transport around the obstacle, achieving transport efficiencies of 70% with negligible heating. Finally we demonstrate the loading of a hybrid optical-magnetic trap with 87Rb and the creation of Bose-Einstein condensates via forced evaporative cooling close to the dielectric surface.
    Guided transport of ultracold gases of rubidium up to a room-temperature dielectric surface
    A L Marchant, S Händel, T P Wiles, S A Hopkins and S L Cornish
    New J. Phys. 13, 125003 (2011)
    We report on the guided transport of an atomic sample along an optical waveguide up to a room-temperature dielectric surface. The technique exploits a simple hybrid trap consisting of a single beam dipole trap positioned ~125 µm below the field zero of a magnetic quadrupole potential. Transportation is realized by applying a moderate bias field (<12 G) to displace the magnetic field zero of the quadrupole potential along the axis of the dipole trap. We use the technique to demonstrate that atomic gases may be controllably transported over 8 mm with negligible heating or loss. The transport path is completely defined by the optical waveguide and we demonstrate that, by aligning the waveguide through a super polished prism, ultracold atoms may be controllably delivered up to a predetermined region of a surface.
    Magnetic merging of ultracold atomic gases of 85Rb and 87Rb
    S Händel, T P Wiles, A L Marchant, S A Hopkins, C S Adams and S L Cornish
    Phys Rev A 83, 053633 (2011)
    We report the magnetic merging of ultracold atomic gases of 85Rb and 87Rb by the controlled overlap of two initially spatially separated magnetic traps. We present a detailed analysis of the combined magnetic-field potential as the two traps are brought together that predicts a clear optimum trajectory for the merging. We verify this prediction experimentally using 85Rb and find that the final atom number in the merged trap is maximized with minimal heating by following the predicted optimum trajectory. Using the magnetic-merging approach allows us to create variable-ratio isotopic Rb mixtures with a single laser-cooling setup by simply storing one isotope in a magnetic trap before jumping the laser frequencies to the transitions necessary to laser cool the second isotope.
    Off-resonance laser frequency stabilization using the Faraday effect
    A L Marchant, S Händel, T P Wiles, S A Hopkins, C S Adams and S L Cornish
    Opt Lett 36, 64 (2011)
    We present a simple technique for stabilization of a laser frequency off resonance using the Faraday effect in a heated vapor cell with an applied magnetic field. In particular, we demonstrate stabilization of a 780 nm laser detuned up to 14 GHz from the 85Rb D252S1/2F=2 to 52P3/2F'=3 transition. Control of the temperature of the vapor cell and the magnitude of the applied magnetic field allows locking ~6-14 GHz red and blue detuned from the atomic line. We obtain an rms fluctuation of 7 MHz over 1h without stabilization of the cell temperature or magnetic field.
Content © Anna Marchant, Durham University 2011