Eoin Seymour Gwyn Phillips
Click here to download thesis: Controlled Dynamics of Laser-Cooled Ions in a Penning Trap
Title: Controlled dynamics of laser-cooled ions in a Penning trap
I report on a scheme for improved control over the motion of small numbers of laser-cooled ions in a Penning trap. This work is part of a larger project to assess the suitability of the Penning trap for quantum information processing (QIP). Laser cooling of ions in this type of trap is complicated by large Zeeman shifts of the cooling- and repumping-transition wavelengths from those in zero magnetic field. Lasers can not, therefore, be tuned to the unshifted atomic spectral lines using an external reference such as a hollow-cathode lamp. In order to address this difficulty I built a wavemeter with a precision of one part in 107 for direct tuning of the lasers to the transition wavelengths. It was also necessary to improve the laser-frequency stabilities by building reference cavities to which they could be locked. In evaluating the suitability of the Penning trap for QIP, one must address the poor localisation of the ions due to the difficulty in cooling one of the radial motions: the magnetron motion. I have implemented a technique called axialisation that reduces this motion's amplitude by coupling it to the other radial motion: the modified cyclotron motion, which is efficiently laser-cooled. This was done with small clouds of magnesium ions and later with small clouds of calcium ions. The damping rate of both radial motions was measured using near-resonant motional excitation and an RF-photon correlation technique. The coupling rate could be inferred from a shift of the motional frequency in a classical analogue of a quantum avoided crossing. Increases in damping rates of the magnetron motion of more than an order of magnitude were observed for both calcium and magnesium ions and coupling rates of order 1 kHz were measured.
Issue Date: December 2004
Supervisor: Thompson, Richard
Item Type: Physics PhD Thesis