Design of Feshbach and Levitation coils for a caesium interferometer with tunable interactions

Abstract

The aim of this diploma thesis is to create two sets of coils: One pair of so-called Levitation coils in anti-Helmholtz conguration and one pair of so-called Feshbach coils in Helmholtz conguration. Both will be used in an experiment which has the aim of creating a compact caesium interferometer with tunable interactions based on a ColdQuanta RuBECi system and an atomchip. In this experiment it is necessary to create a caesium BEC in the F = 3, mF = 3 state which can only be achieved with the help of the magnetic elds produced by the Levitation and Feshbach coils. The aim of the Levitation coils is to levitate and hold the atoms in a crossed dipole trap beneath the atomchip against gravity. Therefore a magnetic field gradient of 31.3G/cm is necessary. The magnetic eld of the Feshbach coilsof 10G - 55G on the other hand can be used to tune the scattering length of the atoms. This is necessary not only to be able to create the caesium BEC in the first place but also to control its phase during the interferometric sequence.After assessing the geometrical constraints due to the compactness of the setup it was clear that an ideal (anti-) Helmholtz conguration wasn't possible for either the Levitation or the Feshbach coils. COMSOL Multiphysics was used to set up a simulation to test and evaluate the fields of both pairs of coils. With the help of this simulations the coils were then optimized to find the ideal current, number of windings, thickness of the wire and distance between the coils, so that they stay as close to room temperature as possible while producing the necessary highly stable and homogeneous elds at the position of the BEC. Afterwards a company was hired to manufacture the coils. Once they arrived they were tested in orderto measure their heating and magnetic field. As it turned out the simulations were very accurate regarding the created magnetic elds and also the heating, although it became apparent that the Levitation coils will need external cooling. Once this issue is solved the coils are ready to help creating and controlling the caesium BEC.