Real-time single-molecule imaging of quantum interference

Abstract

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...

A Green's function approach to modeling molecular diffraction in the limit of ultra‐thin gratings

“…1a we show a typical molecular diffraction experiment, which has been described in more detail in Ref. [9]. It is contained in a vacuum chamber at p < 10 −7 mbar to make sure that the molecules propagate freely from the source to the detector after they were evaporated from the entrance window by a focused laser beam.…”

“…Matter-wave diffraction at a double slit or grating is a paradigmatic example of fundamental quantum physics [1], which has been demonstrated with electrons [2], neutrons [3], atoms [4,5], and small [6,7] and complex molecules [8,9]. Babinet's theorem predicts also quantum fringes in diffraction at opaque obstacles, and Poisson's spot was observed with atoms [10] and diatomic molecules [11] -with an application also in Fresnel zone plates [12].…”

Spatial Coherence Properties of Organic Molecules Coupled to Plasmonic Surface Lattice Resonances in the Weak and Strong Coupling Regimes

“…Inspired by this phenomenon well known for classical radiation, interference experiments were crucial in establishing the wave-particle nature of single photons, as well as massive particles [1][2][3], within quantum mechanics.…”

“…In the experiments [1][2][3] the quantum mechanical wave properties of matter became visible at low temperatures. Here, we consider a different question: the spatial coherence properties of objects, or modes, that are hybrids of wavelike and particlelike components.…”

An atomically thin matter-wave beamsplitter

“…1g,) and reference all images to the diffraction of molecules at 45 nm thick silicon nitride (Fig. 1h) [23]. Figure 1 demonstrates that stable structures can be written even into atomically thin membranes.…”