Coherent Optics for Long-Base-Line Molecule Interferometry

Quantum physics tells us that matter has a much more intriguing character than we usually perceive in our everyday life. While we often think of atoms and molecules as localized building blocks of nature with a well-defined location and momentum, comparable to little Lego blocks, it has been known for 90 years by now that all matter is also associated with a quantum wave function. This wave function carries many characteristics that we know from water waves, acoustics or light: it can spread out, delocalize, diffract and two or more wavelets may also interfere. Quantum physics differs, however, from classical mechanics in that these phenomena even apply to individual atoms or molecules. This surprising fact can be verified by exposing single particles to matter-wave interferometry. Successful early experiments with electrons, neutrons and atoms have stimulated molecule interferometry. Throughout the last years the Quantum Nanophysics Group at the University of Vienna has become home to cluster and molecule diffraction and interference experiments, recently even with molecules composed of more than 800 atoms, weighing as much as 10’000 protons, still the current world record. The refined machines needed for tracking the quantum nature of matter, now also turn out to be highly sensitive force sensors, for molecule metrology as well as for novel tests in fundamental physics.
Within the project COLMI we propose to build LUMI, the first long-baseline matter-wave interferometer, 10 times longer than all previous molecule experiments, and with a versatile choice of diffraction gratings. The proposed instrument will allow us to study and use the quantum wave nature of atoms over biomolecules to metal clusters, under comparable conditions in the same machine. Its extended length and its small grating periods, close the minimum of what is technologically feasible in continuous wave laser technology, will enable quantum interference with de Broglie wavelengths down to 𝜆𝑑𝐵≃ 50 fm i.e. an order of magnitude smaller than in any matter-wave interferometer so far.
For this to become reality, we will explore new beam splitting techniques, advanced interferometer concepts, and we will dedicate substantial efforts to fight external perturbations which become systematically more relevant with the expected more than 100-fold increase in force sensitivity. This includes a new interferometer design, vibration isolation, monitoring, compensation and cross-correlation of subtle effects related to the Earth’s rotation and gravity.
The project will contribute substantially to future tests of the quantum superposition principle and it shall become the basis for one of the finest tools for quantum-based molecule metrology.