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.
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.
These lecture notes emerged from a contribution to the "Les Houches Summer School, Session CVII - Current Trends in Atomic Physics, July 2016". It is meant to serve students as a guide to a selection of topics that are currently at the focus of molecular quantum optics and complements an earlier lecture on related topics [Arndt et al., 2014]. In this review we discuss recent advances in molecular quantum optics with large organic molecules. In particular, we present successful experiments of molecules of biological importance, such as neurotransmitters and map out the route towards interferometry of large bio-matter such as proteins. The interaction of internally complex molecules with various beam splitters is discussed for both far-field diffraction at a single nanomechanical grating and the Kapitza-Dirac Talbot-Lau near-field interferometer - addressing recent progress, experimental challenges, and prospects for quantum enhanced metrology of highly complex systems in the gas phase. A central part of this review deals with the preparation of slow beams of neutral biomolecules, ranging from a single amino acid to proteins or peptides in a micro-environment.
We describe the state of the art in preparing, manipulating and detecting coherent molecular matter. We focus on experimental methods for handling the quantum motion of compound systems from diatomic molecules to clusters or biomolecules.Molecular quantum optics offers many challenges and innovative prospects: already the combination of two atoms into one molecule takes several well-established methods from atomic physics, such as for instance laser cooling, to their limits. The enormous internal complexity that arises when hundreds or thousands of atoms are bound in a single organic molecule, cluster or nanocrystal provides a richness that can only be tackled by combining methods from atomic physics, chemistry, cluster physics, nanotechnology and the life sciences.We review various molecular beam sources and their suitability for matter-wave experiments. We discuss numerous molecular detection schemes and give an overview over diffraction and interference experiments that have already been performed with molecules or clusters.Applications of de Broglie studies with composite systems range from fundamental tests of physics up to quantum-enhanced metrology in physical chemistry, biophysics and the surface sciences.Nanoparticle quantum optics is a growing field, which will intrigue researchers still for many years to come. This review can, therefore, only be a snapshot of a very dynamical process.
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.
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.
We discuss new de Broglie coherence experiments in a near-field molecule interferometer with a variety of large organic molecules. While de Broglie coherence is to first order only associated with the center-of-mass motion of the diffracted particle, we here investigate the question as to which extent the internal molecular property is relevant for, compatible with or detrimental for maintaining coherence in the translational degree of freedom. External perturbations, such as inhomogeneous external electric fields, may influence the delocalized molecules inside the matter wave interferometer and they allow us to access the molecular polarizabilities, permanent or even fluctuating electric dipole moments. We extract information about the molecular states from the interference phase shifts as well as from the observed dephasing in a Kapitza-Dirac Talbot-Lau-Stark-deflectometer. We discuss the relevance of our experiments with regard to both molecule metrology and the foundations of quantum mechanics, i.e. the preservation of coherence for highly complex particles in external fields.
Since de Broglie's work on the wave nature of particles, various optical phenomena have been observed with matter waves of atoms and molecules. However, the analogy between classical and atom/molecule optics is not exact because of different dispersion relations. In addition, according to de Broglie's formula, different combinations of particle mass and velocity can give the same de Broglie wavelength. As a result, even for identical wavelengths, different molecular properties such as electric polarizabilities, Casimir-Polder forces, and dissociation energies modify (and potentially suppress) the resulting matter-wave optical phenomena such as diffraction intensities or interference effects. We report on the universal behavior observed in matter-wave diffraction of He atoms and He2 and D2 molecules from a ruled grating. Clear evidence for emerging beam resonances is observed in the diffraction patterns, which are quantitatively the same for all three particles and only depend on the de Broglie wavelength. A model, combining secondary scattering and quantum reflection, permits us to trace the observed universal behavior back to the peculiar principles of quantum reflection.