Hamid Ohadi

Click here to download thesis: Single Ca+ Ions in a Penning Trap for Applications in Quantum Info Processing

Title: Single Ca⁺ ions in a Penning trap for applications in quantum information processing

Abstract: 

I report on work aimed towards realising Quantum Information Processing with single ⁴⁰Ca⁺ ions in a Penning trap, where trapping is achieved using static electric and magnetic fields. Unlike RF traps, in the Penning trap there is no heating due to micromotion. Therefore the qubit should in principle have a longer decoherence time. However in the Penning trap, the internal levels of the ion shift and split due to the magnetic field. As a result, one needs to implement additional lasers to address the split levels. In the experiment reported here two cooling lasers at 397nm and five repumping lasers at 866nm and 850nm are used. An additional Ti:Sapphire laser has been developed to address the qubit transition at 729nm. Because the natural linewidth of this transition is extremely narrow, the laser needs to be very stable in frequency. For this reason the laser is locked to a stable, high finesse cavity (F ∼ 250, 000) using the Pound-Drever-Hall technique. This brings the stability of the laser from ∼ 3MHz down to 3kHz sufficiently low for the experiments we intend to do in the near future, for example sideband cooling. Previous attempts in our group to trap a single ion in the Penning trap failed due to an unexpectedly low fluorescence count rate per ion. This led us to simulate the cooling dynamics to investigate the possibility that “trapped states” might be the cause. Although there were trapped states in our scheme we were able to show that it was possible to avoid them by appropriately tuning the laser frequencies. Further experimental work showed that the low count rate was due to low laser power in the 866nm repumping lasers. Once this had been addressed we were able to trap and Doppler cool a single ⁴⁰Ca⁺ ion in a Penning trap for the first time. The ion is further cooled using axialisation.

Issue Date: January 2008

Supervisor: Thompson, Richard

                    Segal, Danny

Item Type:  Physics PhD Thesis