Design and commissioning of an experiment for sympathetic cooling and coupling of ions in a cryogenic Penning trap

Abstract

Precise comparisons between the properties of matter and antimatter conjugates constitute a stringent test of CPT and Lorentz symmetries. The proton’s and antiproton’s magnetic moments have recently been measured to high precision in Penning traps, but further progress is impaired by the need to prepare a particle with low motional energy. Current preparation schemes require long preparation times and are limited by high temperatures. Sympathetic laser cooling using an atomic ion has been proposed for preparation of low-energy protons and antipro- tons. This thesis presents the design and commissioning of a cryogenic Penning trap system for sympathetic laser cooling using beryllium ions. The experiment aims to demonstrate direct Coulomb coupling between two particles trapped in nearby, but separate potential wells in a Penning trap stack for the first time. This technique could be used for sympathetic cooling of particles lacking the necessary substructure to apply laser cooling directly. The application of this method on protons and antiprotons has the potential to decrease the mean kinetic energies of the particles and the preparation times required by several orders of magnitude. Furthermore, the method can be extended to other particles, such as highly charged ions. A quantum logic spectroscopy scheme for the measurement of the magnetic moment of the proton and antiproton has been proposed by Heinzen and Wineland. Experimental requirements for realisation of this proposal are discussed. The design of a suitable Penning trap system is described. A cryogenic ultra-high vacuum system cooled by a closed-cycle cryocooler, equipped with an ultra low vibration interface, is designed and commissioned. The necessary infrastructure, such as laser systems and electronics are described. First signals taken from this newly constructed cryogenic Penning trap are presented. Laser ablation trap loading, Doppler cooling and the reduction of the particle number down to a single ion are demonstrated. Prospects of the experiment and implications for the precision of future measurements of the proton’s and antiproton’s magnetic moments augmented by sympathetic laser cooling and elements of quantum logic are discussed.