Probing and controlling quantum magnetism with ultra-cold atoms

Baw Swe. Phyo

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.

Wolfgang Ketterle

Jennie Guzman, Sabrina R. Leslie, Mukund Vengalattore +2 more

Gediminas Juzeliūnas, Julius Ruseckas, Patrik Öhberg

We study the influence of two resonant laser beams (to be referred to as the control and probe beams) on the centre-of-mass motion of ultra-cold atoms characterized by three energy levels of the Λ-type. The laser beams being in the electromagnetically induced transparency (EIT) configuration drive the atoms to their dark states. We impose the adiabatic approximation and obtain an effective equation of motion for the dark state atoms. The equation contains a vector potential type interaction as well as an effective trapping potential. We concentrate on the situation where the control and probe beams are co-propagating and have orbital angular momenta (OAM). The effective magnetic field is then oriented along the propagation direction of the control and probe beams. Its spatial profile can be shaped by choosing proper laser beams. We analyse several situations where the effective magnetic field exhibits a radial dependence. In particular, we study effective magnetic fields induced by Bessel beams, and demonstrate how to generate a constant effective magnetic field for a ring geometry of the atomic trap. We also discuss a possibility of creating an effective field of a magnetic monopole.

T Müller, B Zhang, R Fermani +5 more

We store and control ultra-cold atoms in a new type of trap using the magnetic fields of vortices in a high-temperature superconducting micro-structure. We generate the attractive trapping potential for the atoms by combining the magnetic field of a superconductor in the remanent state with external homogeneous magnetic fields. We show the control of crucial atom trap characteristics such as an efficient intrinsic loading mechanism, spatial positioning of the trapped atoms and the vortex density in the superconductor. The measured trap characteristics are in good agreement with our numerical simulations.

Christian Groß