A. L. Marchant

Controlled formation and reflection of a bright solitary matter-wave

Bright solitons are non-dispersive wave solutions, arising in a diverse range of nonlinear, one-dimensional systems, including atomic Bose–Einstein condensates with attractive interactions. In reality, cold-atom experiments can only approach the idealized one-dimensional limit necessary for the realization of true solitons. Nevertheless, it remains possible to create bright solitary waves, the three-dimensional analogue of solitons, which maintain many of the key properties of their one-dimensional counterparts. Such solitary waves offer many potential applications and provide a rich testing ground for theoretical treatments of many-body quantum systems. Here we report the controlled formation of a bright solitary matter-wave from a Bose–Einstein condensate of 85Rb, which is observed to propagate over a distance of ∼1.1 mm in 150 ms with no observable dispersion. We demonstrate the reflection of a solitary wave from a repulsive Gaussian barrier and contrast this to the case of a repulsive condensate, in both cases finding excellent agreement with theoretical simulations using the three-dimensional Gross–Pitaevskii equation.

A simple, versatile laser system for the creation of ultracold ground state molecules

A narrow-linewidth, dual-wavelength laser system is vital for the creation of ultracold ground state molecules via stimulated Raman adiabatic passage (STIRAP) from a weakly bound Feshbach state. Here we describe how a relatively simple apparatus consisting of a single fixed-length optical cavity can be used to narrow the linewidth of the two different wavelength lasers required for STIRAP simultaneously. The frequency of each of these lasers is referenced to the cavity and is continuously tunable away from the cavity modes through the use of non-resonant electrooptic modulators. Self-heterodyne measurements suggest the laser linewidths are reduced to several hundred Hz. In the context of 87Rb133Cs molecules produced via magnetoassociation on a Feshbach resonance, we demonstrate the performance of the laser system through one- and two-photon molecular spectroscopy. Finally, we demonstrate transfer of the molecules to the rovibrational ground state using STIRAP.

Quantum reflection of bright solitary matter waves from a narrow attractive potential

We report the observation of quantum reflection from a narrow attractive potential using bright solitary matter waves formed from a Rb 85 Bose-Einstein condensate. We create the attractive potential using a tightly focused, red-detuned laser beam, and observe reflection of up to 25% of the atoms, along with the confinement of atoms at the position of the beam. We show that the observed reflected fraction is much larger than theoretical predictions for a simple Gaussian potential well. A more detailed model of bright soliton propagation, accounting for the generic presence of small subsidiary intensity maxima in the red-detuned beam, suggests that these small intensity maxima are the cause of this enhanced reflection.

Bright Solitary Matter Waves: Formation, Stability and Interactions

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 asymmetric collisions. We review the experimental formation and observation of bright solitary matter waves to date, and compare to theoretical predictions. Finally we discuss some topical aspects, including beyond-mean-field descriptions, symmetry breaking, exotic bright solitary waves, and proposals to exploit bright solitary waves in interferometry and as surface probes.

Magnetic transport apparatus for the production of ultracold atomic gases in the vicinity of a dielectric surface

We present an apparatus designed for studies of atom-surface interactions using quantum degenerate gases of (85)Rb and (87)Rb 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 (87)Rb and the creation of Bose-Einstein condensates via forced evaporative cooling close to the dielectric surface.

Bose-Einstein condensation of 85 Rb by direct evaporation in an optical dipole trap

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 4×104 atoms and demonstrate the tunable nature of the atomic interactions.

Measuring the disorder of vortex lattices in a Bose-Einstein condensate.

We report observations of the formation and subsequent decay of a vortex lattice in a Bose-Einstein condensate confined in a hybrid optical-magnetic trap. Vortices are induced by rotating the anharmonic magnetic potential that provides confinement in the horizontal plane. We present simple numerical techniques based on image analysis to detect vortices and analyze their distributions. We use these methods to quantify the amount of order present in the vortex distribution as it transitions from a disordered array to the energetically favorable ordered lattice.

Magnetic merging of ultracold atomic gases of 85Rb and 87Rb

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.

Repeated output coupling of ultracold Feshbach molecules from a Cs BEC

We investigate magnetoassociation of ultracold Feshbach molecules from a Bose-Einstein condensate of Cs atoms and explore the spectrum of weakly bound molecular states close to the atomic threshold. By exploiting the variation of magnetic field experienced by a molecular cloud falling in the presence of a magnetic field gradient, we demonstrate the repeated output coupling of molecules from a single atomic cloud using a Feshbach resonance at 19.89 G. Using this method we are able to produce up to 24 separate pulses of molecules from a single atomic condensate, with a molecular pulse created every 7.2 ms. Furthermore, by careful control of the magnetic bias field and gradient we are able to utilise an avoided crossing in the bound state spectrum at 13.3 G to demonstrate exquisite control over the dynamics of the molecular clouds.