The wave nature of matter is a cornerstone of modern physics and has been demonstrated for a wide range of fundamental and composite particles. While diffraction at nanomechanical masks is usually regarded to be independent of internal atomic or molecular states, the particles' polarizabilities and dipole moments lead to dispersive interactions with the grating surface. In prior experiments, such forces largely prevented coherent diffraction of polar molecules as they induce dephasing of the matter wave in the presence of randomly distributed charges inside the grating. Here, we show that surface milling using neon ions facilitates the fabrication of lowly charged nanomasks in gold-capped silicon nitride membranes. This allows us to observe diffraction of polar molecules with over four times larger electric dipole moment than in previous experiments, opening a path towards distinction of structural conformers in matter-wave experiments. Published by the American Physical Society 2024
We investigate the influence of different electric moments on the shift and dephasing of molecules in a matter wave interferometer. Firstly, we provide a quantitative comparison of two molecules that are non-polar yet polarizable in their thermal ground state and that differ in their stiffness and response to thermal excitations . While C 25 H 20 is rather rigid, its larger derivative C 49 H 16 F 52 is additionally equipped with floppy side chains and vibrationally activated dipole moment variations. Secondly, we elucidate the role of a permanent electric dipole moment by contrasting the quantum interference pattern of a (nearly) non-polar and a polar porphyrin derivative. We find that a high molecular polarizability and even sizeable dipole moment fluctuations are still well compatible with high-contrast quantum interference fringes. The presence of permanent electric dipole moments, however, can lead to a dephasing and rapid degradation of the quantum fringe pattern already at moderate electric fields. This finding is of high relevance for coherence experiments with large organic molecules, which are generally equipped with strong electric moments.
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. image
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.
Even 100 years after its introduction by Louis de Broglie, the wave-nature of matter is often regarded as a mind-boggling phenomenon. To give an intuitive introduction to this field, we here discuss the diffraction of massive molecules through a single, a double, and a triple slit, as well as a nanomechanical grating. While the experiments are in good agreement with undergraduate textbook predictions, we also observe pronounced differences resulting from the molecules' mass and internal complexity. The molecules' polarizability causes an attractive van der Waals interaction with the slit walls, which can be modified by rotating the nanomechanical mask with respect to the molecular beam. The text is meant to introduce students and teachers to the concepts of molecule diffraction, supported by problems and solutions that can be discussed in class.
Abstract Self-imaging in near-field diffraction is a practical application of coherent manipulation of matter waves in Talbot interferometry. In this work, near-field diffraction of protons by a nanostructured metallic grating under the influence of (a) uniform, (b) spatially modulated, and (c) temporally modulated electric fields are investigated. Time-domain simulations of two-dimensional Gaussian wave packets for protons are performed by solving the time-dependent Schrödinger’s equation using the generalized finite difference time domain method for quantum systems. Effects of strength (E 0) and orientation (θ) of the uniform electric field on the diffraction properties, such as fringe pattern, intensity of the peaks, fringe shift, and visibility, are investigated. The results show that the Talbot fringes shift significantly in the transverse direction even for a small change in the applied electric field ( <?CDATA
ΔE0=0.1?> Δ E 0 = 0.1 V m−1) and its orientation ( <?CDATA
Δθ=0.1∘?> Δ θ = 0.1 ∘ ). Moreover, electric field-dependent fringe visibility is observed, which can be tuned by E 0 and θ. The potential barriers arising from a spatially modulated electric field are observed to cause significant distortions in the Talbot patterns when the modulation length ( <?CDATA
λ′?> λ ′ ) is equal to the de Broglie wavelength ( <?CDATA
λdB?> λ d B ). Sidebands are observed in the Talbot pattern due to the efficient transfer of energy from the oscillating field to the wave packet when the frequency of oscillation (ω) is of the order of ω 0 ( <?CDATA $ = 2\pi/T_0$?> = 2 π / T 0 ), where T 0 is the interaction time. This study will be helpful in uniform electric field-controlled precision metrology, developing a highly sensitive electric field sensor based on Talbot interference, and precisely aligning the matter wave optical setup. Furthermore, the sidebands in the Talbot fringe can be used as a precise tool for momentum splitter in matter wave interferometry.