Achieving Cooling Without Repump Lasers Through Ion Motional Heating

TL;DR

This paper demonstrates a novel laser cooling method for Be+ ions that eliminates the need for repump lasers by using ion micromotion heating, enabling simpler and more efficient ion cooling techniques.

Contribution

The study introduces a new approach to laser cooling that leverages ion micromotion heating, removing the requirement for repump lasers and simplifying ion cooling setups.

Findings

Achieved cooling of Be+ ions with a single laser beam.

Controlled ion micromotion to reach velocities up to 3144 m/s.

Molecular dynamics simulations accurately reproduced experimental results.

Abstract

Laser cooling typically requires one or more repump lasers to clear dark states and enable recycling transitions. Here, we have achieved cooling of Be+ ions using a single laser beam, facilitated by one-dimensional heating through micromotion. By manipulating the displacement from the trap's nodal line, we precisely controlled the ion micromotion direction and speed, reaching up to 3144 m/s, which corresponds to a 7.1 GHz Doppler frequency shift in our experiment. This approach eliminates the necessity of a 1.25 GHz offset repump laser while keeping the Be+ ions cold in the perpendicular direction. Measurements were taken using cooling laser detuning and imaging of ion trajectories. Molecular dynamics simulations, based on machine learned time-dependent electric field E(X, Y, Z, t) inside the trap, accurately reproduced the experimental observation, illuminating the relationship between the direction of micromotion and the trapping electric filed vector. This work not only provides a robust method for managing the micromotion velocity of ions but also sheds light on laser cooling complex systems that require multiple repumping lasers. Additionally, it offers a method for controlling energy in the context of ion-molecule collision investigations.