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Fractional photon-assisted tunnelling of ultra-cold atoms in periodically shaken double-well lattices
M Esmann, J D Pritchard, C Weiss
Laser Phys. Lett. 9, 160 (2012)

Fractional photon-assisted tunneling is investigated both numerically and analytically in a double-well lattice. While integer photon-assisted tunneling is a single-particle effect, fractional photon-assisted tunneling is an interaction-induced many-body effect. Double-well lattices with few particles in each double well are ideal to study this effect far from the mean-field effects. It is predicted that the 1/4-resonance is observable in such systems. Fractional photon-assisted tunneling provides a physically relevant model, for which N-th order time-dependent perturbation theory can be large although all previous orders are small. All predicted effects will be observable with an existing experimental setup [1].

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, and 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. 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.

Polarization spectroscopy of an excited state transition
C. Carr, C.S. Adams and K.J. Weatherill
Opt. Lett. 37, 118 (2012)

We demonstrate polarization spectroscopy of an excited state transition in room-temperature cesium vapor. An anisotropy induced by a circularly polarized pump beam on the D2 transition is observed using a weak probe on the 6P_3/2 -> 7S_1/2 transition. At high pump power, a subfeature due to Autler-Townes splitting is observed that theoretical modeling shows is enhanced by Doppler averaging. Polarization spectroscopy provides a simple modulation–free signal suitable for laser frequency stabilization to excited state transitions.

Coherence and instability in a driven Bose–Einstein condensate: a fully dynamical number-conserving approach
T. P. Billam and S. A. Gardiner
New Journal of Physics 013038 14, 013038 (2012)

We consider a Bose–Einstein condensate driven by periodic δ-kicks. In contrast to first-order descriptions, which predict rapid, unbounded growth of the noncondensate in resonant parameter regimes, the consistent treatment of condensate depletion in our fully time-dependent, second-order description acts to damp this growth, leading to oscillations in the (non)condensate population and the coherence of the system.

Variational determination of approximate bright matter-wave soliton solutions in anisotropic traps
T. P. Billam, S. A. Wrathmall, and S. A. Gardiner
Physical Review A 85, 013627 (2012)

We consider the ground state of an attractively interacting atomic Bose-Einstein condensate in a prolate, cylindrically symmetric harmonic trap. If a true quasi-one-dimensional limit is realized, then for sufficiently weak axial trapping this ground state takes the form of a bright soliton solution of the nonlinear Schrödinger equation. Using analytic variational and highly accurate numerical solutions of the Gross-Pitaevskii equation, we systematically and quantitatively assess how solitonlike this ground state is, over a wide range of trap and interaction strengths. Our analysis reveals that the regime in which the ground state is highly solitonlike is significantly restricted and occurs only for experimentally challenging trap anisotropies. This result and our broader identification of regimes in which the ground state is well approximated by our simple analytic variational solution are relevant to a range of potential experiments involving attractively interacting Bose-Einstein condensates.

Distinguishing mesoscopic quantum superpositions from statistical mixtures in periodically shaken double wells
C Weiss
J. Phys. B: At. Mol. Opt. Phys. 45, 021002 (2012)

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

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 ( less than 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.

An analytical model of off-resonant Faraday rotation in hot alkali metal vapours
Stefan L Kemp, Ifan G Hughes and Simon L Cornish
J. Phys. B: At. Mol. Opt. Phys. 44 235004

We report a thorough investigation of the Faraday effect on the 852 nm D2 transition in a hot caesium vapour, culminating in the development of a simple analytical model for off-resonant Faraday rotation. The model, applicable to all hot alkali metal vapours, is seen to predict the rotation observed in caesium, at temperatures as high as 115 °C, to within 1% accuracy for probe light detuned by greater than 2 GHz from the D2 lines.

Absolute absorption on the rubidium D1 line including resonant dipole–dipole interactions
L Weller, R J Bettles, P Siddons, C S Adams, I G Hughes
J. Phys. B: At. Mol. Opt. Phys. 44 195006

Here we report on measurements of the absolute absorption spectra of dense rubidium vapour on the D1 line in the weak-probe regime for temperatures up to 170 °C and number densities up to 3 × 1014 cm−3. In such vapours, modifications to the homogeneous linewidth of optical transitions arise due to dipole–dipole interactions between identical atoms, in superpositions of the ground and excited states. Absolute absorption spectra were recorded with a deviation of 0.1% between experiment and a theory incorporating resonant dipole–dipole interactions. The manifestation of dipole–dipole interactions is a self-broadening contribution to the homogeneous linewidth, which grows linearly with number density of atoms. Analysis of the absolute absorption spectra allows us to ascertain the value of the self-broadening coefficient for the rubidium D1 line: β/2π = (0.69 ± 0.04) × 10−7 Hz cm3, in excellent agreement with the theoretical prediction.

Realizing bright matter-wave soliton collisions with controlled relative phase
TP Billam, SL Cornish, SA Gardiner
Phys Rev A 83, 041602(R) (2011) [arXiv]

We propose a method to split the ground state of an attractively interacting atomic Bose-Einstein condensate into two bright solitary waves with controlled relative phase and velocity. We analyze the stability of these waves against their subsequent recollisions at the center of a cylindrically symmetric, prolate harmonic trap as a function of relative phase, velocity, and trap anisotropy. We show that the collisional stability is strongly dependent on relative phase at low velocity, and we identify previously unobserved oscillations in the collisional stability as a function of the trap anisotropy. An experimental implementation of our method would determine the validity of the mean-field description of bright solitary waves and could prove to be an important step toward atom interferometry experiments involving bright solitary waves.

Off-resonance laser frequency stabilization using the Faraday effect
AL Marchant, S Händel, TP Wiles, SA Hopkins, CS Adams, SL 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 780nm laser detuned up to 14GHz from the Rb85D252S1/2F=2 to 52P3/2F′=3 transition. Control of the temperature of the vapor cell and the magnitude of the applied magnetic field allows locking ∼6–14GHz red and blue detuned from the atomic line. We obtain an rms fluctuation of 7MHz over 1h without stabilization of the cell temperature or magnetic field.