Towards A Non-Destructive Single Molecular Ion State Readout And Rotational Inelastic Collisions Between Molecular Nitrogen Ions and Argon Atoms

Precision spectroscopy on narrow dipole-forbidden transitions in trapped ultra-cold ions can be used to investigate a possible time-variation of fundamental constants like the fine-structure constant or the proton-to-electron mass ratio. For the investigation of the proton-to-electron mass ratio, molecular ions, like N+2, can possibly offer a higher precision than atomic ions. But due to the lack of closed-cycling transitions in most molecular and many atomic ions, the state detection of these ions remains challenging and often destructive readout techniques have to be employed. In recent years, various techniques to overcome these limitations were proposed and some experimentally demonstrated. These techniques make use of the shared motion of the spectroscopic ion and a co-trapped laser-coolable atomic ion to couple the two ions dependent on the internal state of the spectroscopic ion and determine the state via the co-trapped ion.
Here, a simple and robust non-destructive state readout technique for ultra-cold co-trapped N+2 ions based on exciting the shared motion of the ground-state cooled two-ion system by the optical dipole force of an off-resonant optical lattice is presented. The properties and behavior of this non-destructive readout are investigated theoretically and possible implementations and transitions in N+2 are evaluated. In a second step, the properties of this non-destructive state readout scheme were characterized on laser-cooled Ca+ ions and a first trial on single N+2 ions was attempted. Tough designed for N+2 , the technique presented in here can be easily adopted for other ions lacking closed-cycling transition as well.
Moreover, the rotational inelastic collision rate between cold N+2 ions in the vibrational ground state and neutral Ar atoms was experimentally re-investigated in this thesis. Recent theoretical studies indicated that the rate of these inelastic collisions could be larger than previously measured. Therefore, the inelastic collision rate wit Ar was re-investigated using trapped and sympathetically cooled N+2 ions.