Ion-atom hybrid systems

The study of interactions between simultaneously trapped cold ions and atoms has emerged as a new research direction in recent years. The development of ion-atom hybrid experiments has paved the way for investigating elastic, inelastic and reactive collisions between these species at very low temperatures, for exploring new cooling mechanisms of ions by atoms and for implementing new hybrid quantum systems. The present lecture reviews experimental methods, recent results and upcoming developments in this emerging field.Comment: To appear in the Proceedings of the International School of Physics Enrico Fermi, Course 189: Ion Traps for Tomorrows Application

Fine- and hyperfine-structure effects in molecular photoionization: II. Resonance-enhanced multiphoton ionization and hyperfine-selective generation of molecular cations

Resonance-enhanced multiphoton ionization (REMPI) is a widely used technique for studying molecular photoionization and producing molecular cations for spectroscopy and dynamics studies. Here, we present a model for describing hyperfine-structure effects in the REMPI process and for predicting hyperfine populations in molecular ions produced by this method. This model is a generalization of our model for fine- and hyperfine- structure effects in one-photon ionization of molecules presented in the preceding companion article. This generalization is achieved by covering two main aspects: (1) treatment of the neutral bound-bound transition including hyperfine structure that makes up the first step of the REMPI process and (2) modification of our ionization model to account for anisotropic populations resulting from this first excitation step. Our findings may be used for analyzing results from experiments with molecular ions produced by REMPI and may serve as a theoretical background for hyperfine-selective ionization experiments

Optimised surface-electrode ion-trap junctions for experiments with cold molecular ions

We discuss the design and optimisation of two types of junctions between surface-electrode radiofrequency ion-trap arrays that enable the integration of experiments with sympathetically cooled molecular ions on a monolithic chip device. A detailed description of a multi-objective optimisation procedure applicable to an arbitrary planar junction is presented, and the results for a cross junction between four quadrupoles as well as a quadrupole-to-octupole junction are discussed. Based on these optimised functional elements, we propose a multi-functional ion-trap chip for experiments with translationally cold molecular ions at temperatures in the millikelvin range. This study opens the door to extending complex chip-based trapping techniques to Coulomb-crystallised molecular ions with potential applications in mass spectrometry, spectroscopy, controlled chemistry and quantum technology.Comment: 19 pages, 10 figure

Molecules and Ions at Very Low Temperatures

The generation and study of 'cold' gas-phase molecules characterised by very low translational temperatures Ttrans ? 1 K is an upcoming field of research in physical chemistry which has received considerable attention over the past years. A particular interesting form of cold molecules are ensembles of cold localised cations in ion traps which form ordered structures known as 'Coulomb crystals'. The present article reviews the experimental methods used for the generation of atomic and molecular Coulomb crystals and highlights recent experiments which take advantage of their intriguing properties in order to study chemical reactions at very low temperatures with single-particle sensitivity

Molecular-ion quantum technologies

Quantum-logic techniques for state preparation, manipulation, and non-destructive interrogation are increasingly being adopted for experiments on single molecular ions confined in traps. The ability to control molecular ions on the quantum level via a co-trapped atomic ion offers intriguing possibilities for new experiments in the realms of precision spectroscopy, quantum information processing, cold chemistry, and quantum technologies with molecules. The present article gives an overview of the basic experimental methods, recent developments and prospects in this field

Molecular-ion quantum technologies

Quantum-logic techniques for state preparation, manipulation, and non-destructive interrogation are increasingly being adopted for experiments on single molecular ions confined in traps. The ability to control molecular ions on the quantum level via a co-trapped atomic ion offers intriguing possibilities for new experiments in the realms of precision spectroscopy, quantum information processing, cold chemistry, and quantum technologies with molecules. The present article gives an overview of the basic experimental methods, recent developments and prospects in this field

Forbidden Vibrational Transitions in Cold Molecular Ions: Experimental Observation and Potential Applications

A range of interesting fundamental scientific questions can be addressed by high-precision molecular spectroscopy. A promising way towards this goal is the measurement of dipole-forbidden vibrational transitions in molecular ions. We have recently reported the first such observation in a molecular ion. Here, we give an overview of our method and our results as well as an outlook on potential future applications

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

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