Over the past years, the development of experimental techniques for the coherent manipulation and control of single isolated quantum systems has made impressive progress. Such "quantum-logic" methods are also highly attractive in a chemical context in view of unravelling and controlling the quantum dynamics of molecular collisions and chemical reactions. However, for complex quantum systems like molecules, these techniques are still in their infancy and their considerable potential remains to be unlocked. The aim of the present project is to merge the fields of quantum science and chemical dynamics by advancing quantum technologies to polyatomic molecular ions and applying them to the study of ion-molecule collisions and chemical reactions. For this purpose, we have recently developed a quantum-non-demolition technique which enables the readout and spectroscopy of the quantum state of a single molecular ion without destroying the molecule or even perturbing its quantum state [Science 367 (2020), 1213]. In the present project, we will apply this method to achieve a complete projective state preparation of single molecular ions in specific Zeeman- hyperfine-spin-rovibronic levels as a starting point for collision studies and use the same methods to sen- sitively detect the quantum state of the collision product. In this way, state-to-state experiments on the single-molecule level will be realised using a quantum-logic state readout. In combination with Stark- decelerated beams of neutral molecules, we will be able to study for the first time completely state- and energy-controlled ion-molecule elastic, inelastic and reactive collisions. In particular, we will be able to explore the role of the hyperfine and Zeeman states in collisions involving molecular ions, which is largely uncharted territory. The quantum-non-demolition nature of our detection scheme will allow us to reach measurement sensitivities several orders of magnitude higher compared to previously used destruc- tive methods and thus enable an unprecedented precision in the study of ionic collisional processes. By introducing quantum-logic approaches to the study of molecular collisions, the present project will establish a new paradigm for probing molecular processes and a new frontier in studies of chemical dy- namics. The extension of our methods to polyatomics will also make a broad range of molecular systems available for applications in the quantum sciences including quantum bits, quantum memories, quantum simulations and quantum sensing.

In recent years, impressive advances in the cooling, manipulation and quantum control of ultracold trapped atoms and atomic ions have been achieved which enabled spectroscopic measurements with an unprecedented precision. Similarly precise spectroscopic experiments on molecules open up a range of new scientific perspectives including tests of new physical concepts, the implementation of new fre- quency standards, accurate evaluations of physical theories such as quantum electrodynamics, precise determinations of fundamental constants and exact studies of the properties of molecules and their con- stituent particles. They also lay the foundations for applications of molecules in the realm of modern quantum science such as quantum information and quantum sensing. However, the complex energy-level structure of molecules and the absence of optical cycling transitions in most molecular systems constitute a major challenge for their state preparation, laser cooling, state detection, coherent manipulation and, therefore, precise spectroscopic characterisation. Molecular ions confined in radiofrequency traps and sympathetically cooled by simultaneously trap- ped atomic ions have proven a promising route for overcoming these obstacles. We have recently devel- oped a new experimental scheme enabling the readout of the quantum state of a single trapped molecular ion without destroying the molecule and indeed the quantum state itself. This quantum-non-demolition technique enables spectroscopic experiments with four to five orders of magnitude faster duty cycles than previous destructive state-readout techniques and concomitant improvements in spectroscopic sensitivity and precision. Such "quantum-logic" methods represent a paradigm change in the way spectroscopic experiments are performed on molecules. In the present project, we will harness the potential of this new approach to perform highly sensitive spectroscopic measurements on the hyperfine, rotational and vibrational energy- level structure of the homonuclear diatomic ion N+2 with unprecedented precision. N+2 has previously been identified as an ideal system for molecular precision measurements. In a recent comprehensive the- oretical screening, we have explored suitable clock transitions within the energy-level manifolds of N+2 which will be characterised experimentally in the present project. We will make use of a newly estab- lished infrastructure for the distribution of the Swiss primary frequency standard at the Swiss metrology institute METAS in Berne to our laboratory in Basel via an optical fibre link. Referencing all our laser sources to the METAS standard will allow us to reach an absolute measurement precision on the level of 10−15 thus establishing a new frontier in the precision of spectroscopic measurements on molecular ions across different frequency domains. The clock transitions to be probed here are predicted to also exhibit excellent coherence properties and are therefore attractive candidates for molecular quantum bits with prospective applications in quantum science. In summary, using quantum-logic techniques for state readout in combination with remote calibration to the Swiss primary frequency standard via a fibre link, the present project will introduce new methods for molecular frequency metrology and establish new limits in the measurement precision of the hyper- fine, rotational and vibrational spectroscopy of molecular ions. In this framework, we will also perform the first direct rotational spectroscopy on a homonuclear diatomic ion. Besides their immediate relevance for molecular spectroscopy, the targeted results are expected to be of importance for the wider field of frequency metrology and the development of new frequency standards, for atomic, molecular, optical and chemical physics by introducing new concepts to probe and interrogate molecules, for quantum science by establishing quantum bits with very high coherence properties and also for fundamental physics by setting new constraints on a possible time variation of the electron-proton mass ratio.

Following the resounding successes with atomic and solid-state systems, the development of quantum technologies for molecular systems has made rapid progress over the past few years. The experiments pursued rely on the entanglement of single molecular ions trapped together with single atomic ions. The atom serves the purpose of cooling the molecule and acting as a probe for the molecule by state readout through a suitable quantum protocol. These approaches have enabled the fully coherent manipulation of single isolated molecules thus opening up a wealth of exciting research directions in the molecular sciences. Experiments in this domain have so far focused on applications of this technology in molecular spectroscopy and precision measurements. In the present PhD project, we will harness state-preparation and readout methods recently developed in our group to probe for the first time collisional and chemical properties on the single-molecule level in a fully coherent manner. Specifically, we will prepare single molecules in well-defined quantum and motional states in an ion trap and monitor their collisions with other molecules. Changes of their quantum state, translational energy and chemical composition will be monitored in real time by readout of these properties using an entangled atomic ion. We expect that this new approach will provide new insights into molecular collisions, molecular energy transfer and chemical transformations at a level of detail which has not been attainable before. The project is highly interdisciplinary connecting the quantum sciences, molecular physics and chemistry in a new and original fashion.

Studies of the dynamics of chemical reactions have made impressive advances in recent years owing to the development of techniques for the cooling and manipulation of the motion of molecules in the gas phase. These methods have enabled new insights into the microscopic mechanisms, the quantum nature and the detailed dynamics of chemical processes which were not accessible before. By combining trapped, sympathetically cooled molecular ions with electrostatically deflected molec- ular beams, we have recently established a new experimental approach for studying reactive collisions of trapped molecular ions with state- and conformationally controlled neutral molecules. While we have so far achieved state, collision-energy and conformational control for the neutral reactants using the elec- trostatic deflection technique, the quantum state and conformation of the ionic co-reactant has not been specified in our previous experiments. To achieve a comprehensive control over a reactive process by predetermining its most important dynamical parameters, it is necessary to specify the quantum state and conformation of both reactants. In the present grant application, we propose to additionally generate polyatomic molecular ions in the vibrational ground state of specific conformational isomers in order to realise a fully vibrationally, conformationally and collision-energy-controlled ion-molecule reaction experiment for the first time. This will be achieved by preparing the ions using conformer-selective pho- toionisation techniques in combination with sympathetic cooling of their translational motion in an ion trap. Our new methodology will be applied to study conformationally and state-specific dynamics in a range of pertinent model systems including the reactions of rotationally state-selected water molecules and of conformationally selected 3-aminophenol molecules with conformationally selected phenylala- nine and 3-aminophenol ions. The experimental results on the kinetics and reaction dynamics of these systems will be complemented and analysed by quasiclassical-trajectory simulations on accurate ab-initio potential energy surfaces. We expect that these advancements will take the study of ion-molecule chemistry of polyatomic sys- tems to a new level and enable insights into their state- and geometry-specific reaction dynamics, kinetics and mechanisms in unprecedented detail. The present grant application is thematically fully embedded in the COST Action CA17113 - TIPICQA "Trapped Ions: Progress in classical and quantum applications" and capitalises on scientific synergies through collaborations and scientific exchanges within Workgroup 4 "Hybrid Systems" of this Action.

The reaction rates and dynamics of chemical reactions and molecular energy transfer are often influenced by the structure of the involved molecules. Even subtle changes of the molecular geometry can make significant differences in chemical reactivity. Both intramolecular and intermolecular processes need to be understood on the quantum level in molecular systems with well-defined geometries in order to establish a detailed understanding of structure- reactivity relationships. The present project aims at establishing a comprehensive characterisation of these relationships in selected model systems by studying both collisional and half-collisional reactions by pooling the expertise of the Korean and Swiss partners. Combined structural and quantum aspects of chemical reaction dynamics will be studied under precisely controlled conditions in the gas phase. State-of-the-art experimental techniques such as Stark deflection, double-resonance, stimulated-emission pumping and hole-burning will be employed in order to spatially or spectroscopically isolate specific conformational isomers of the molecules in the gas phase. This will enable the study of half-collisional reactions such as photodissociation, intramolecular tunnelling, and isomerization as well as state-selective full collisional reactions in a conformer-specific manner. Measurements of conformationally resolved spectra and reaction-rate constants will be complemented by frequency and/or time resolved velocity-map ion/electron imaging experiments to elucidate fine details of the reaction dynamics. The systems targeted in this study are hydroquinone, resorcinol and oxalyl chloride and their reactions with free radicals such as F, Cl and OH which have been selected for their prototypical character and experimental amenability. In addition to the bare conformationally selected molecules, investigations will also be performed with their conformationally selected clusters with water in order to study the effects of incipient solvatisation on the reactivity and dynamics. Moreover, vibrationally state-selected studies will be performed to gain insights into the interplay between mode- and structure-specific reactive effects. The experiments will be complemented by ab-initio and reactive molecular dynamics calculations to analyse and interpret the data. Spectroscopic characterization of conformers and their half-collisional dynamics will be studied at KAIST in Korea, whereas full collisional dynamics involving conformer-specific neutral-radical will be investigated at University of Basel in Switzerland. The partner groups constitute an ideal match to carry out the present research programme by sharing similar research interests, but contributing complementary scientific expertise, techniques and equipment. The project relies on harvesting the synergies between the groups through the exchange of knowledge, of experimental techniques and of data as well as through the joint training of PhD students and regular scientific visits of the involved personnel between Switzerland and Korea. By for the first time contrasting intra- with inter-molecular dynamics in selected geometry- selected model systems, we expect that the present project will yield new and valuable insights into structure-reactivity relationships in chemistry. We expect that the present results will not only be of immediate relevance for the advancement of molecular and chemical physics, but will also contribute to the general understanding of chemical reactivity and be of specific benefit to a wider range of disciplines such as synthetic chemistry and catalysis.

The goal of this project is to exploit recent progress in laser technology, frequency metrology and molecule optics to carry out ultra-precise measurements of energy intervals between electronic, vibrational and rotational states of molecules, in particular molecular ions. The present project aims to achieve a relative measurement accuracy in molecular-ion spectroscopy of order 10−14 −10−15, an improvement of several orders of magnitude in comparison to the present state of the art of 10−9. These advancements will open up a new frontier in precision molecular spectroscopy which will pave the way for using molecules as new high-precision frequency standards and clocks, for addressing fundamental physical problems such as the proton-radius puzzle and a possible temporal variation of fundamental physical constants and for precision tests of quantum electrodynamics. All of these application will be explored in the present project. The dramatic advancement in measurement accuracy targeted here will be enabled by the implementation of new spectroscopic methodologies based on quantum technologies, by the de- velopment of ultranarrow quantum-cascade laser sources tailored to the present needs, and in particular through the implementation of a fibre-optical network for the distribution of the Swiss primary frequency standard maintained by the Federal Institute of Metrology METAS to spec- troscopy laboratories in Basel and Zurich. This network will enable the absolute stabilisation, calibration and frequency comparison of the laser sources employed in the present measurements at a level of up to 10−15 by their referencing to the Swiss primary standard. While several Eu- ropean countries have already set up similar national and international networks for precision frequency distribution, Switzerland thus far possesses no such facilities. For Switzerland not to lose contact and competitiveness in the key future scientific domain of frequency metrology, it is imperative for our country to establish similar infrastructures. The present project will establish and test a prototype network connecting ETH Zurich, the University of Basel and the Federal Institute of Metrology METAS in Bern/Wabern. This prototype is intended to form the nucleus of a Swiss national network for precision frequency- and time distribution linking a broad range of national laboratories and research groups involved in frequency metrology in the future. These objectives can only be reached through the close collaboration of a highly interdisci- plinary team involving physical chemists, laser physicists, metrologists and telecommunication- network engineers which are assembled in the present project.

Enabled by the recent development of experimental techniques for the simultaneous trapping of cold ions and atoms, the study of interactions between these species at temperatures down to the millikelvin range has emerged as a new scientific field at the interface between chemistry and physics over the past few years. These "hybrid" systems of cold ions and atoms have formed the basis of exciting new avenues of research. These include studies of the dynamics of ion-neutral collisions at very low energies, the elucidation of exotic ultralow-temperature ion chemistry, the investigation of many-body physics in a regime of intermediate interaction strengths, precise characterizations of intermolecular interactions and the development of new cooling techniques for ions.One major drawback of previous experiments, however, was their technological restriction to laser- coolable atoms, mostly alkalis, which were confined in suitable atom traps and superimposed with trapped ions. This experimental limitation severely constrained the scope of systems and phenomena which could be studied. As the main objective of our current SNSF project over the past two years, we have been developing a new experimental approach for the simultaneous trapping of cold neutral molecules and molecular ions which substantially enhances the chemical and scientific scope of hybrid trapping experiments. Our new method is based on the magnetic trapping of Stark-decelerated cold neu- tral molecules which are superimposed with sympathetically cooled molecular ions in a radiofrequency ion trap under cryogenic conditions. This new experimental setup opens the dorr for probing interactions, collisions and chemical reactions between ions and molecules in the millikelvin regime for the first time.Following the experimental development of this new method during the first phase of the project, we now apply for a continuation of this project grant to harvest its full scientific potential by (i) implementing internal quantum-state preparation of both the trapped neutrals and the trapped ions in order to realize fully state-controlled studies, (ii) further extending its chemical scope by trapping a wider range of neutral molecules and molecular ions, and (iii) apply these developments to investigations of cold collisions and chemical reactions in a range of prototypical and fundamental ion-molecule hybrid systems consisting of the combination of N2+ , O2+ and H2O+ with OH and NH.The present project combines experimental methods established in the domains of quantum optics and atomic and molecular physics in a new and original fashion in order to address pertinent problems in chemistry and chemical physics. It will introduce new experimental techniques into studies of the collisional and chemical dynamics of ionic processes which enable an unprecedented level of control over collision parameters such as collision energies and molecular quantum states. In this way, it will provide new insights into fundamental principles of molecular energy transfer, chemical reactivity and collision dynamics of interest to a wider chemistry and physics community

Editorship for Molecular Physics - A Journal at the Interface of Chemsitry and Physics

We propose to couple for the first time a cold ion in an ion trap to a nanomechanical oscillator consisting of metallic nanowire, establishing a new type of quantum interface between a single atom and a solid-state device. We will realize resonant coupling between the two systems mediated by electric fields and will use the nanowire to manipulate the quantum motion of the ion. The present project stands right at the interface between quantum science, quantum optics and nanoscience and will introduce nano-techniques into quantum optics in a new and original fashion. The present proposal is laid out as a collaboration between the Willitsch and Poggio groups, combining the complementary expertise of both groups in a highly interdisciplinary project. The results of the present project open up perspectives for a new research direction, i.e., ion-solid state interfaces, with potential applications in fields as diverse as quantum technology, the nanosciences, mass spectrometry and chemical sensing.

The relationship between structure and reactivity is one of the central tenets of chemistry. In particular, many molecules exhibit structural isomers that interconvert over low barriers through rotations about covalent bonds (conformers). Conformers are the dominant isomers of complex molecules, and the conformation of a molecule can have pronounced effects on its chemical reactivity. Despite the eminent importance of conformational isomers in chemistry, very few studies have been reported thus far charac- terising conformational effects in chemical reactions under single-collision conditions. Consequently, the role of molecular conformations in fundamental reactions is only poorly understood. This striking lack of data reflects the experimental challenges to isolate und control specific conformers. In a recent proof-of-principle study [ Science 342 (2013), 98], we have spatially separated specific con- formers in a molecular beam through electrostatic deflection and directed them at a spatially localized reaction target of cold ions in a trap. This approach allowed us to study conformation-specific effects in ion-molecule reactions under precisely controlled experimental conditions in the gas phase. Here, we pro- pose a wide-ranging research programme aiming at extending our method to neutral reactions and applying it to a range of chemically relevant problems in order to explore the relationship between structure and reactivity in unprecedented detail. These methodological advances will enable for the first time detailed and systematic studies of the reaction mechanisms and dynamics of isolated conformers. The fundamental mechanistic insights gained will benefit a wide range of fields as diverse as fundamental reaction dynamics, organic synthesis, catalysis, atmospheric chemistry and rational molecule design.