In recent years, matter-wave diffraction at nanomechanical structures has been used by several research groups to explore the quantum nature of atoms and molecules, to prove the existence of weakly bound molecules or to explore atom-surface interactions with high sensitivity. The particles' Casimir-Polder interaction with the diffraction grating leads to significant changes in the amplitude distribution of the diffraction pattern. This becomes particularly intriguing in the thin-grating limit, i.e. when the size of a complex molecule becomes comparable with the grating thickness and its rotation period comparable to the transit time through the mask. Here we analyze the predictive power of a Green's function scattering model and the constraints imposed by the finite control over real-world experimental factors on the nanoscale.

Matter-wave interferometry has become an essential tool in studies on the foundations of quantum physics [1] and for precision measurements [2][3][4][5][6]. Mechanical gratings have played an important role as coherent beamsplitters for atoms [7], molecules and clusters [8,9] since the basic diffraction mechanism is the same for all particles. However, polarizable objects may experience van der Waals shifts when they pass the grating walls [10,11] and the undesired dephasing may prevent interferometry with massive objects [12]. Here we explore how to minimize this perturbation by reducing the thickness of the diffraction mask to its ultimate physical limit, i.e. the thickness of a single atom. We have fabricated diffraction masks in single-layer and bilayer graphene as well as in 1 nm thin carbonaceous biphenyl membrane. We identify conditions to transform an array of single layer graphene nanoribbons into a grating of carbon nanoscrolls. We show that all these ultra-thin nanomasks can be used for high-contrast quantum diffraction of massive molecules. They can be seen as a nanomechanical answer to the question debated by Bohr and Einstein [13] whether a softly suspended double slit would destroy quantum interference. In agreement with Bohr's reasoning we show that quantum coherence prevails even in the limit of atomically thin gratings.

Matter waves pass multipath interference test.