The quantum superposition principle, a key distinction between quantum physics and classical mechanics, is often perceived as a philosophical challenge to our concepts of reality, locality or space-time since it contrasts with our intuitive expectations with experimental observations on isolated quantum systems. While we are used to associating the notion of localization with massive bodies, quantum physics teaches us that every individual object is associated with a wave function that may eventually delocalize by far more than the body's own extension. Numerous experiments have verified this concept at the microscopic scale but intuition wavers when it comes to delocalization experiments with complex objects. While quantum science is the uncontested ideal of a physical theory, one may ask if the superposition principle can persist on all complexity scales. This motivates matter-wave diffraction and interference studies with large compounds in a three-grating interferometer configuration which also necessitates the preparation of high-mass nanoparticle beams at low velocities. Here we demonstrate how synthetic chemistry allows us to prepare libraries of fluorous porphyrins which can be tailored to exhibit high mass, good thermal stability and relatively low polarizability, which allows us to form slow thermal beams of these high-mass compounds, which can be detected using electron ionization mass spectrometry. We present successful superposition experiments with selected species from these molecular libraries in a quantum interferometer, which utilizes the diffraction of matter-waves at an optical phase grating. We observe high-contrast quantum fringe patterns of molecules exceeding a mass of 10,000 amu and having 810 atoms in a single particle.
The quantum superposition principle, a key distinction between quantum physics and classical mechanics, is often perceived as a philosophical challenge to our concepts of reality, locality or space-time since it contrasts with our intuitive expectations with experimental observations on isolated quantum systems. While we are used to associating the notion of localization with massive bodies, quantum physics teaches us that every individual object is associated with a wave function that may eventually delocalize by far more than the body's own extension. Numerous experiments have verified this concept at the microscopic scale but intuition wavers when it comes to delocalization experiments with complex objects. While quantum science is the uncontested ideal of a physical theory, one may ask if the superposition principle can persist on all complexity scales. This motivates matter-wave diffraction and interference studies with large compounds in a three-grating interferometer configuration which also necessitates the preparation of high-mass nanoparticle beams at low velocities. Here we demonstrate how synthetic chemistry allows us to prepare libraries of fluorous porphyrins which can be tailored to exhibit high mass, good thermal stability and relatively low polarizability, which allows us to form slow thermal beams of these high-mass compounds, which can be detected using electron ionization mass spectrometry. We present successful superposition experiments with selected species from these molecular libraries in a quantum interferometer, which utilizes the diffraction of matter-waves at an optical phase grating. We observe high-contrast quantum fringe patterns of molecules exceeding a mass of 10,000 amu and having 810 atoms in a single particle.
The wave nature of matter is a key ingredient of quantum physics and yet it defies our classical intuition. First proposed by Louis de Broglie a century ago, it has since been confirmed with a variety of particles from electrons up to molecules. Here we demonstrate new high-contrast quantum experiments with large and massive tailor-made organic molecules in a near-field interferometer. Our experiments prove the quantum wave nature and delocalization of compounds composed of up to 430 atoms, with a maximal size of up to 60 Å, masses up to m=6,910 AMU and de Broglie wavelengths down to λdB=h/mv≃1 pm. We show that even complex systems, with more than 1,000 internal degrees of freedom, can be prepared in quantum states that are sufficiently well isolated from their environment to avoid decoherence and to show almost perfect coherence. Observing superposition states of mesoscopic quantum systems is an ongoing challenge. Gerlichet al. report quantum interference of large tailor-made organic compounds, demonstrating delocalization and the quantum wave nature of entire molecules composed of up to 430 atoms.
Matter-wave dualism is a fundamental concept in quantum physics. The observation of wave properties of heavy organic molecules can be used to approach the borderline between classical and quantum physics. Up to which mass and size do particles or molecules still have wave properties? This question is subject to be answered within this thesis and as part of the international nanoquestfit-project where many researchers of different disciplines are involved. \nThis thesis is a summary of the work done within a research collaboration between the group of Prof. Dr. Marcel Mayor (University of Basel) and the group of Prof. Dr. Markus Arndt (University of Vienna). The work is mainly focused on the development of novel quantum interference experiments that imply the development of new synthetic strategies towards tailor-made molecules. Novel interferometers have been developed by the Arndt group and therefore the molecular requirements changed strongly within the past years. The syntheses of these tailor-made molecules were performed by the author in the laboratories of Prof. Mayor in Basel. Quantum interference experiments and the preliminary investigations described within this work, namely the thermal stability test, the desorption studies and the laser-induced acoustic desorption have been performed by the Arndt group in Vienna. \nInvestigations at the interface of quantum and classical physics are a fascinating part of the research. The final goal is to approach the quantum-to-classical transition by the observation of quantum properties of large and complex molecules. In order to study the wave nature of such particles—a purely quantum mechanical phenomenon—synthetic procedures towards tailor-made compounds are developed to improve the observation of this phenomenon through matter-wave experiments. \nAt the starting point of this work, a series of highly fluorinated porphyrin-monomers set a new benchmark in high-mass quantum interference experiments. The highest masses of particles used in quantum interference experiments were around 10’000 g/mol. Thus, our objective was to reach masses up to 25’000 g/mol with the suitable features for the quantum interferometry experiments. \nIn the first chapter of this thesis, the principle of interferometry, the development and evolution of this technology are presented. In the subsequent chapters, the different synthetic approaches of the tailor-made molecules designed to improve the measurements and achieve the goal of this thesis are described. \nThe main part of this thesis is focused on the synthesis of tailor-made molecules for quantum interference experiments. In a first part, the synthesis of a novel, more massive fluorinated phthalocyanine is presented. That phthalocyanine was used in far-field quantum interference experiments. Unfortunately, the molecular requirements could not been tuned to observe wave-particle duality in these experiments. The second part focuses on the synthesis of three different molecular libraries. Molecular libraries are mixtures of molecules having the same core but a to some extent random number of long perfluorinated chains. The individual members within the library were observable in MALDI-TOF mass spectrometry. We attached the chains to three different cores to obtain three different molecular libraries. To produce a first generation of libraries we used diacetylene bond porphyrin-dimer. The rather limited reaction scope of diacetylene bond porphyrins was enhanced by the second generation of tetramers and pentamers. To compare the modularity of the synthesis of oligo-porphyrin systems two additional cores, a porphyrin-dimer and a porphyrin-trimer, have also been synthesized. The possibility to produce a molecular beam with the three molecular-libraries has been investigated by thermal studies, desorption experiments and laser-induced acoustic desorption. \nThe last part of the thesis is focused on the synthesis of photocleavable tags that can be attached to model compounds. These tags are synthesized since novel quantum interference experiments are based on light gratings where a mass difference is supposed to be observed at the detector level upon cleavage. The final idea is, in the near future, to attach these molecules to large particles, such as metal-nanoparticles, clusters or proteins. It is expected to enable the detection of mass differences of the intact clusters and the clusters with the cleaved tags. Three different model compounds have been synthesized. The cleavage of the tags was proven in solution upon irradiation of UV-light in solution, where a constant and reproducible decay was observed. In future quantum interference experiments, the cleavage should be performed in gas-phase as a final prove of concept. The molecules are currently under investigations in the Arndt group.
In order to explore the quantum-to-classical transition, the ambition of this thesis was the design and synthesis of tailor-made molecules for matter-wave interference experiments. Firstly, the focus was set on a deeper understanding of the influence of a molecule’s internal structure, especially its polarizability, on quantum interference. Furthermore, the limits of quantum mechanics were addressed by increasing the size of the interfering objects. The metrological aspect of molecule interferometry - to measure influences of molecule properties on the wave nature - is described in the first part of this thesis. Two fourfold perfluorohexyl functionalized constitutional isomers were synthesized in order to demonstrate that different molecular conformations can be distinguished in quantum interference experiments. A tetrahedral isomer and a rod-like oligo(phenylene ethynylene) derivative were applied in a near-field Kapitza-Dirac-Talbot-Lau interferometer. Although de Broglie quantum interference describes the center of mass motion of a massive body, it was shown to be sensitive to the internal molecular structure of the constitutional isomers. The different total susceptibilities of both isomers lead to different de Broglie interference shifts in the presence of external electric fields. The isomers thus become distinguishable in spite of their identical mass and chemical sum formula. Besides metrological applications, a main goal of this thesis was to synthesize model compounds for molecule interferometry to increase the preexisting mass record for quantum interferometry, which was held by the fluorofullerene C60F48 with a molecular weight of 1 633 g/mol. Near-field interferometry is a promising concept to set new records and thus to approach the quantum-to-classical transition. To meet the requirements of quantum studies with complex organic molecules in a Kapitza-Dirac-Talbot-Lau near-field interferometer – high volatility, high stability, and high molecular mass – we chose the functionalization of tetraarylporphyrins with perfluoroalkyl moieties. A modular synthesis of seven perfluoroalkyl-substituted porphyrin derivatives with up to 16 fluorous alkyl chains was presented. With this series in hand, it was possible to observe interference patterns for three of the seven derivatives. The heaviest molecule of this series for which the wave nature has been observed has a 3.3 fold higher molecular weight than the preexisting mass record for quantum interference. These experiments open a new window for quantum experiments with nanoobjects in a complexity class comparable to that of small proteins. The experimental setup of the near-field Kapitza-Dirac-Talbot-Lau interferometer is not restricted to monodisperse and pure starting compounds. It also allows for experiments with compound mixtures because individual components of compound libraries can be detected in the mass spectrometric detection unit. The preparation of porphyrin libraries gave access to compounds in a new mass region (> 10 000 g/mol). Preliminary investigations in near-field interferometers with these structures revealed suitable molecule beam properties. With these porphyrin libraries in hand, it is expected to exceed for the first time the ceiling of 10 000 g/mol for an interfering object in the future. Large, stable, highly volatile and fluorescent molecules were the goal of synthetic work that was performed for novel far-field interference experiments in a setup based on fluorescence detection. For this purpose three fluorescent fluorous phthalocyanine derivatives were prepared. With the help of a new laser-controlled micro-evaporation source it was possible to produce a beam of molecules with the required intensity and coherence. The observation of the wave nature of a free base phthalocyanine having a molecular weight of 1 299 g/mol set a new mass record for far-field molecule interferometry. The preexisting record for far-field interferometry was held by the fullerene C70 with a mass of 841 g/mol. To conclude, major contributions to the exploration of the frontiers of quantum mechanics were achieved by matter-wave interferometry using the perfluoroalkyl-functionalized molecules described in this thesis. \n
Recent progress and future prospects of matter-wave interferometry with complex organic molecules and inorganic clusters are reviewed. Three variants of a near-field interference effect, based on diffraction by material nanostructures, at optical phase gratings, and at ionizing laser fields are considered. The theoretical concepts underlying these experiments and the experimental challenges are discussed. This includes optimizing interferometer designs as well as understanding the role of decoherence. The high sensitivity of matter-wave interference experiments to external perturbations is demonstrated to be useful for accurately measuring internal properties of delocalized nanoparticles. The prospects for probing the quantum superposition principle are investigated in the limit of high particle mass and complexity.
Abstract The quantum superposition principle is a fundamental concept of physics 1 and the basis of numerous quantum technologies 2,3 . Yet, it is still often regarded counterintuitive because we do not observe its key features on the macroscopic scales of our daily lives. It is, therefore, interesting to ask how quantum properties persist or change as we increase the size and complexity of objects 4 . A model test for this question can be realized by matter-wave interferometry, in which the motion of individual massive particles becomes delocalized and needs to be described by a wave function that spans regions far larger than the particle itself 5 . Over the years, this has been explored with a series of objects of increasing mass and complexity 6–9 and a growing community aims at pushing this to ever larger limits. Here we present an experimental platform that extends matter-wave interference to large metal clusters, a qualitatively new material class for quantum experiments. We specifically demonstrate quantum interference of sodium nanoparticles, which can each contain more than 7,000 atoms at masses greater than 170,000 Da. They propagate in a Schrödinger cat state with a macroscopicity 10 of μ = 15.5, surpassing previous experiments 5,9,11 by an order of magnitude.
The chapter discusses advances in matter-wave optics with complex molecules, generalizing Young’s double slit to high masses. The quantum wave-particle duality is visualized by monitoring the arrival patterns of molecules diffracted at nanomechanical masks. Each molecule displays particle behavior when it is localized on the detector; however, the overall interference pattern requires their delocalization in free flight. Internal particle properties influence the de Broglie waves in the presence of surfaces or fields—even in interaction with atomically thin gratings. To probe the quantum nature of high-mass molecules, universal beam splitters are combined in a multi-grating interferometer to observe high-contrast matter-wave fringes even for 500 K hot molecules, containing 810 atoms with a mass of 10 000 amu. The high sensitivity of the nanoscale interference fringes to deflection in external fields enables non-invasive measurements of molecular properties. The chapter concludes by discussing research on beam techniques that extend molecular quantum optics to large biomolecules.