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.

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 observation of interference patterns in double-slit experiments with massive particles is generally regarded as the ultimate demonstration of the quantum nature of these objects. Such matter-wave interference has been observed for electrons 1 , neutrons 2 , atoms 3,4 and molecules [5][6][7] and it differs from classical wave-physics in that it can even be observed when single particles arrive at the detector one by one. The build-up of such patterns in experiments with electrons has been described as the "most beautiful experiment in physics" [8][9][10][11] . Here we show how a combination of nanofabrication and nanoimaging methods allows us to record the full two-dimensional build-up of quantum diffraction patterns in real-time for phthalocyanine molecules PcH2 and their tailored derivatives F24PcH2 with a mass of 1298 amu. A laser-controlled micro-evaporation source was used to produce a beam of molecules with the required intensity and coherence and the gratings were machined in 10-nm thick silicon nitride membranes to reduce the effect of van der Waals forces. Wide-field fluorescence microscopy was used to detect the position of each molecule with an accuracy of 10 nm and to reveal the build-up of a deterministic ensemble interference pattern from stochastically arriving and internally hot single molecules.When Richard Feynman described the double-slit experiment with electrons as "at the heart of quantum 2 physics" 12 he was emphasizing the fundamentally non-classical nature of the superposition principle which allows the quantum wave function associated with a massive object to be widely delocalized, while the object itself is always observed as a well-localized particle. Several recent experiments contributed to a further sharpening of the discussion by demonstrating the stochastic build-up of interferograms 11,13 , by implementing double-slit diffraction in the time-domain 14,15 , even down to the attosecond level 16 , and by identifying a single molecule as the smallest double-slit for electron interference 17,18 that enables fundamental decoherence studies 19 . The extension of far-field diffraction 20 to large molecules requires a sufficiently intense and coherent beam of slow and neutral molecules, a nanosized diffraction grating and a detector with both a spatial accuracy of a few nanometers and a molecule specific detection efficiency of close to 100 %. Our present experiment solves all these tasks simultaneously, using advanced micro-preparation, nanodiffraction and nanoimaging technologies. It thus exposes the quantum wave-particle duality in a particularly clear way and opens the way to new studies with ever larger molecules in an ongoing exploration of the quantumclassical borderline.Our setup is shown in Figure 1. It is divided into three parts: the beam preparation, coherent manipulation and detection. We need to prepare the molecules such that each of them interferes with itself and that all of them lead to similar interference patterns on the screen. Since the transverse and longitudina...

Here we describe the design, synthesis, and characterization of new, metal-functionalized, amphiphilic diblock copolymers for molecular recognition. Polybutadiene-block-polyethylenoxide copolymers were synthesized by living anionic polymerization and end group functionalized with nitrilotriacetic acid and tris(nitrilotriacetic acid). After complexation with nickel and copper, these groups are known to selectively bind to oligohistidine residues of proteins. The polymers were characterized by 1H NMR spectroscopy, size exclusion chromatography, electron paramagnetic resonance, and UV-vis spectroscopy. Mixtures of these polymers with the respective nonfunctionalized block copolymers self-assemble in aqueous solution into vesicular structures with a controlled density of the metal complex end-groups on their surface. The accessibility of these binding sites was tested using maltose binding protein carrying a terminal decahistidine moiety and His-tagged enhanced green fluorescent protein as model systems. Fluorescence correlation spectroscopy clearly showed a significant and selective binding of these proteins to the vesicle surface.

Quantum interferometry can serve as a useful complement to mass spectrometry. The interference visibility (see picture) reveals important information on molecular properties, such as mass and polarizability. The method is applicable to a wide range of molecules, and is particularly valuable for characterizing neutral molecular beams. In particular, fragmentation in the source can be distinguished from molecular dissociation in the detector.