Valliappan Letchumanan

This thesis was based in NPL. 

Click here to download thesis: Coherent Control and Ground State Cooling of a Single 88Sr+ Ion

Title: Coherent control and ground state cooling of a single ⁸⁸Sr⁺ ion

Abstract: 

This thesis describes experiments using a single ⁸⁸Sr⁺ ion. The ion is confined in a radio-frequency end-cap trap and laser cooled on the strong 5s ²S_1/2 – 5p ²P_1/2 cooling transition. Spectroscopic investigations are performed on the narrow 5s ²S_1/2 – 4d ²D_5/2 quadrupole transition.

A precision measurement of the ²D_5/2 state lifetime has been made. The decay times of an ion prepared in the ²D_5/2 state are measured using Dehmelts electron shelving technique and analysed using several different fitting and estimation methods. A comparison of the these complementary techniques is made and systematic effects are discussed.

By driving the quadrupole transition, the electronic state of the ion has been coherently manipulated to create superpositions of the ²S_1/2 and ²D_5/2 states and Rabi oscillations observed. The rate of dephasing of these oscillations has been used to determine the mean motional quantum numbers of the Doppler cooled ion. High motional quantum numbers after Doppler cooling have been observed in the first endcap trap used. A second endcap trap has been constructed in which cooling to lower motional quantum numbers has been achieved.

Ramsey spectroscopy has been performed on a Zeeman component of the quadrupole transition. The first demonstration of Ramsey and Silsbee’s phase modulation techniques in the optical domain is presented. With this method, increased signal to noise fringes and dispersion shaped curves have been observed and stabilisation of the laser to the transition demonstrated. To simulate these experiments, optical Bloch equations describing the Ramsey oscillatory field method have been set up and solved numerically.

Sub-Doppler cooling may be achieved by resolved-sideband cooling on the quadrupole transition. To realise an acceptable cooling rate, the ²D_5/2 state is quenched using a laser tuned close to the ²P_3/2 – ²D_5/2 transition. The resulting ac-Stark shift of the quadrupole transition has been characterised. Resolved-sideband cooling of the ion using the lower axial sideband of the m_j = −1/2 – m_j = −5/2 component of the quadrupole transition has been demonstrated.

Issue Date: May 2004

Supervisor: Segal, Danny

                    Sinclair, Alastair (NPL)

Item Type:  Physics PhD Thesis