Sympathetic cooling of rovibrationally state-selected molecular ions

TL;DR

This paper introduces a novel method combining state-selective photoionization and sympathetic cooling to produce rovibrationally state-selected, translationally cold molecular ions, enabling advanced quantum-controlled experiments.

Contribution

The authors develop a new technique for preparing state-selected molecular ions with high selectivity and long lifetimes, expanding capabilities for cold ion-molecule research.

Findings

Achieved > 90% selectivity in preparing ground rovibrational states.

Demonstrated ion state lifetimes of approximately 15 minutes.

Applicable to a wide range of molecular ions in various rovibrational states.

Abstract

We present a new method for the generation of rotationally and vibrationally state-selected, translationally cold molecular ions in ion traps. Our technique is based on the state-selective threshold photoionization of neutral molecules followed by sympathetic cooling of the resulting ions with laser-cooled calcium ions. Using N$_2^+$ ions as a test system, we achieve > 90 % selectivity in the preparation of the ground rovibrational level and state lifetimes on the order of 15 minutes limited by collisions with background-gas molecules. The technique can be employed to produce a wide range of apolar and polar molecular ions in the ground and excited rovibrational states. Our approach opens up new perspectives for cold quantum-controlled ion-molecule-collision studies, frequency-metrology experiments with state-selected molecular ions and molecular-ion qubits.