Optimized strategies for the quantum-state preparation of single trapped nitrogen molecular ions

TL;DR

This paper presents optimized two-step strategies for preparing single nitrogen molecular ions in specific quantum states within an ion trap, combining threshold photoionization and measurement-based purification to enhance state purity.

Contribution

It introduces a combined approach of threshold photoionization and quantum-non-demolition detection for high-fidelity preparation of molecular ions in desired quantum states.

Findings

Achieved 38% fidelity in preparing ground-state N2+ ions.

Demonstrated effective state purification by discarding non-target ions.

Characterized a resonance-enhanced photoionization scheme for N2+.

Abstract

This work examines optimized strategies for the preparation of single molecular ions in well-defined rotational quantum states in an ion trap with the example of the molecular nitrogen ion N2+. It advances a two-step approach consisting of an initial threshold-photoionization stage which produces molecular ions with a high probability in the target state, followed by a measurement-based state purification of the sample. For this purpose, a resonance-enhanced threshold photoionization scheme for producing N2+ in its rovibrational ground state proposed by Gardner et al. [Sci. Rep. 9, 506 (2019)] was characterized. The molecular state was measured using a recently developed quantum-non-demolition state-detection method finding a total fidelity of 38(7)% for producing ground-state N2+ under the present experimental conditions. By discarding ions from the trap not found to be in the target state, essentially state-pure samples of single N2+ ions can be generated for subsequent state-specific experiments.