In this presentation we report an achievement of a persistent supercurrent atom chip and trapping87Rb atoms in the vicinity of a cold surface. Persistent supercurrent, up to 2.5 A without Joule heating, was switched on and off by using an on-chip thermal switch that was operated with a laser and a magnetic field. An intensity of the induced supercurrent was controlled by the magnitude of the initially applied z-bias field. We present our experimental results on the characteristics of our atom trap including stability, decoherence time, and influence of the chip surface.
We have trapped rubidium atoms in the magnetic field produced by a superconducting atom chip operated at liquid helium temperatures. Up to $8.2\ifmmode\times\else\texttimes\fi{}{10}^{5}$ atoms are held in a Ioffe-Pritchard trap at a distance of $440\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ from the chip surface, with a temperature of $40\text{ }\text{ }\ensuremath{\mu}\mathrm{K}$. The trap lifetime reaches 115 s at low atomic densities. These results open the way to the exploration of atom-surface interactions and coherent atomic transport in a superconducting environment, whose properties are radically different from normal metals at room temperature.
Atom chips are micro-fabricated devices which create versatile magnetic potentials for trapping, cooling and controlling ensembles of ultra-cold atoms. Advancing from the typical atom chips, currents from superconducting vortices are used to trap and manipulate the ultra-cold atoms in our experiments. The superconducting vortex traps can be configured by controlling strength and pulse time of external magnetic fields together with bias fields. In order to fully utilize reconfigurability, superconducting vortices are optically manipulated with laser light to generate desired vortex patterns with this tailored trapping potentials for ultra-cold atoms are created. We have carried out heat diffusion simulations of laser patterns and characterized laser power and pulse time to effectively configure the desired vortex potentials. We have also successfully manipulated vortex matter optically to create arbitrary vortex patterns and ring potentials for cold atoms to utilize in quantum simulations and on-chip matter wave interferometry applications. Moreover, cold atoms could be used as a sensitive probe to examine magnetic field distribution of the superconducting vortices and we have used this technique to experimentally verify the resulting magnetic potentials of superconducting vortices after optical manipulation. v First of all, I would like to express my heartfelt gratitude and appreciation to my teacher and mentor, Prof.
Atom chips are an excellent tool for studying ultracold degenerate quantum gases, due to the high degree of controllability afforded by the precise potentials generated from the current-carrying microfabricated wires on the chip surface. The geometries of the trapping potentials are inherently capable of realising extreme aspect ratios, and therefore creating model systems with effectively reduced dimensionality, particularly the theoretically-tractable one-dimensional Bose gas. In addition, the temporal tunability makes it possible to impart non-adiabatic changes on the trapping potentials, allowing experimental investigation of samples which have been brought out of equilibrium - a situation which is not fully theoretically understood. This thesis describes the implementation, development and characterisation of an experimental system for producing the first Bose-Einstein condensates of atomic rubidium 87 gas trapped on the surface of an atom chip in Nottingham. Such an apparatus is very complex and requires careful characterisation in order to run in a stable and reliable way. Details of the experimental setup are thoroughly outlined, including the vacuum system, lasers, electronics, computer control and timing, and the optical imaging system. A newly installed compact two-dimensional magneto-optical trap provides an loading rate of 5e7 atoms per second for loading a three-dimensional mirror-magneto-optical trap with 1.5e8 atoms, at a temperature of 300uK within 10s. The cloud is then sub-Doppler cooled to 50uK, and spin-polarised with 96% purity into the |F=2,mF=+2> ground state within 5ms, in preparation for loading a purely magnetic trap. A millimeter sized copper Z-shaped conductor located beneath the atom chip surface creates a Ioffe-Pritchard magnetic trap, into which the laser cooled cloud is loaded with 70% efficiency, and can be held with a vacuum-limited lifetime of 40s. Evaporative cooling then pre-cools the sample to below 20uK within 10s, to allow the subsequent loading into potentials created by the atom chip with 100% efficiency. A final evaporation stage then cools the cloud below the phase transition temperature of 800nK, resulting finally in pure BECs with
105 atoms confined using the atom chip. Key measurements of various properties of the trapped condensates are presented, which are important in order to characterise the system fully, and to compare with theoretical expectations. In particular, included are the variation of condensate fraction with temperature, the BEC expansion dynamics, and the condensate lifetime in the trap, for example. Finally, it is demonstrated how BECs can be produced on the atom chip without the use of external macroscopic coils, achieved by using novel, integrated sheet structures located beneath the chip surface - unique to this experimental system - to create the necessary bias fields.
We investigate superconducting chip structures for trapping and manipulating atoms. These structures are based on the average magnetic field of vortices induced in a type-II superconducting thin film. This magnetic field is the critical ingredient of the demonstrated vortex-based atom trap, which operate without transport current. We employ the hysteretic behavior of a superconducting thin film in the remanent state to generate different traps and flexible magnetic potentials for ultra-cold atoms. The experimental realization can be described by the Bean’s critical-state method to model the vortex field through mesoscopic super currents induced in the thin strip. Various vortex patterns can be obtained by programming different loading-field and transport current sequences. Furthermore we will discuss the expected enhanced lifetime of atoms trapped close to a superconducting surface in comparison with a metallic surface.