Sean Donnellan

Click here to download thesis: Towards Sideband Cooling of a Single 40Ca+ Ion in a Penning Trap

Title: Towards sideband cooling of a single ⁴⁰Ca⁺ ion in a Penning trap

Abstract: 

This thesis presents work aimed towards achieving sideband cooling of ⁴⁰Ca⁺ ions in a Penning trap.

The observation of an increase in the number of quantum jumps as a function of the trapping magnetic field is first presented. This observation is explained by the ion falling into a long-lived D_5/2 state, out of which the ion is not being re-pumped. The ion can fall into this state due to mixing of the fine structure components with the same m_J quantum number induced by the applied magnetic field. A calculation of the mixing and shelving rate as a function of magnetic field strength is presented. This theory matches well with the experimental results observed. This work has been presented in a publication in which a perturbative analysis was used. An alternative analysis is presented here in which the full Hamiltonian is diagonalised. The essential conclusions however remain unchanged.

This ‘J-state mixing’ effect means re-pumping from each of the six D_5/2 state sub-levels of our ion is required for efficient laser cooling. This is achieved by the addition of a system comprising an 854 nm laser and a fibre EOM to provide the radiation required to re-pump these levels. The same EOM is then used to re-pump out of the four sub-levels of the D_3/2 state using a single 866 nm laser. This is a great simplification of the experimental setup required to cool a 40Ca+ ion in a Penning trap which would otherwise require ten separate lasers to independently address each of the D sub-states.

Achieving efficient repumping leads to the ability to perform pulsed spectroscopy on the quadrupole S_1/2 → D_5/2 transition in ⁴⁰Ca⁺. Preliminary results of this spectroscopy in a radio-frequency trap are presented.

Issue Date: 21 November 2011

Supervisor: Thompson, Richard

                    Segal, Danny

Item Type:  Physics PhD Thesis