A magnetic lattice and macroscopic entanglement of a BEC on an atom chip

Atom chips provide a convenient platform to study ultracold quantum gases and their interactions with electromagnetic fields, surfaces, micro-magnetic structures, superconducting circuits and nanomechanical systems. The research work presented in this thesis is classified in two major categories. The first part is focused on the development and construction of a permanent magnetic lattice on an atom chip and the study of trapped atoms in the permanent magnetic lattice potential. In the second part, a new experiment is proposed to create a macroscopic entanglement between the flux state of a superconducting loop and a Bose-Einstein condensate (BEC) on a superconducting atom chip. The permanent magnetic lattice potential is produced by applying a uniform bias magnetic field to a grooved silicon structure coated with a permanent magnetic film. The magnetic film consists of a multilayer structure of GdTbFeCo with perpendicular intrinsic magnetization. The permanent magnetic structure is mounted beneath a current carrying wire structure glued to a ceramic insulator. The current carrying wires assist in the preparation of the ultracold atoms and for loading into the magnetic lattice. In addition, the current carrying wires are used to produce a BEC in a Z- wire magnetic trap. The magnetic lattice potential is produced by a one-dimensional array of highly anisotropic and extremely tight magnetic microtraps of period 10 ¹m. A detailed study of the reflection dynamics of atoms in the magnetic lattice potential is presented along with numerical simulations. Finally, the trapping of atoms in the permanent magnetic lattice at a distance less than 5 ¹m from the surface of the atom chip is described. The properties of the trapped atoms including lifetime, temperature and trap frequency are discussed. A maximum radial trap frequency of about 90 kHz is measured in the magnetic lattice potential with no confinement applied along the axial direction. A new experiment which combines the quantum coherent dynamics in superconducting circuits and BEC manipulation on a superconducting atom chip is proposed and investigated. It is shown how a macroscopic entanglement can be produced between the flux state of a superconducting loop and the state of a BEC trapped in a magnetic trap. In addition, the detection of the macroscopic entanglement based on a quantum eraser and an entangled BEC interference is discussed. Thus, this proposal provides a platform to realise interferometry with an entangled BEC and to explore the quantum-classical interface.