Supervisor: Prof Danny Segal, Prof Richard Thompson

Phase transitions in small ion Coulomb crystals in Penning Traps

In the ion trapping group at Imperial we trap small numbers of calcium ions using a Penning trap. This is a type of ion trap that uses static electric and magnetic fields in confine ions spatially. Lasers are then used to perform Doppler cooling and to manipulate the quantum state of the ion.

Much of the work done so far in my PhD has involved laser stabilisation of the Doppler cooling lasers so that a single ion can be cooled at a constant rate, which enables us to perform laser spectroscopy on a narrow linewidth atomic transition over long periods without the temperature of the ion changing. The aim of this high resolution spectroscopy is to observe the ‘sideband’ structure of the transition which appears due to the quantum motion of the ion in the trap potential. Once stable sideband spectra can be taken then cooling below the Doppler limit can be achieved by placing the spectroscopy laser on the red sideband so that energy is taken from the ion.

In future we would like to perform spectroscopy of this kind on Coulomb crystals of small numbers of ions. Coulomb crystals are configurations where the forces on the ion due to the trap potential and due to Coulomb repulsion balance. The exact geometry of these crystals can be manipulated by changing the trap parameters (electrode voltages, radio frequency drives, ion cooling rate, etc.). Once sideband spectroscopy and cooling of Coulomb crystals has been achieved the quantum nature of the transition between different geometries can be studied.

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