Experimental Improvement of Signal of a Single Laser-Cooled Trapped ^40Ca^＋ Ion

Fei Zhou, You-Yang Xu, Yi Xie +5 more

S. Donnellan

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 D5/2 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 mJ 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 D5/2 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 D3/2 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 S1/2 → D5/2 transition in 40Ca+ . Preliminary results of this spectroscopy in a radio-frequency trap are presented.

Cassius D'Helon

Shu Hua-Lin, Bin Guo, Guan Hua +3 more

A single 40 Ca + ion is loaded in a miniature Paul trap and the probability of directly loading a single ion is above 50%. The signal-to-noise ratio and the storage time for a single ion have been improved by minimizing the ion micromotion and locking a 397 nm cooling laser to a Fabry–Perot interferometer and optogalvanic signal. From the fluorescence spectrum, the ion temperature is estimated to be about 5 mK.

Markus Lindberg

Chang-Da-Ren Fang, Yao Huang, Hua Guan +2 more

We investigate the process of pulsed laser cooling using a self-constructed molecular dynamics simulation (MD-Simulation) program. We simulate the Doppler cooling process and pulsed laser Doppler cooling process of a single 40Ca+ ion, and the comparison with the experimental results shows that this self-constructed MD-Simulation program works well in the weak laser intensity situation. Furthermore, we analyze the pulsed laser Doppler cooling process of a single 27Al+ ion. This program can be used to analyze the molecular dynamic process of various situations of Doppler cooling in an ion trap, which could give predictions and experimental guidance.