Interferometry with tunable matter waves - iWave

Particle-wave-duality is one of the cornerstones of quantum physics. Assigning wave properties to rest-mass particles such as atoms enables the construction of matter wave optics, in particular atom interferometers and gyroscopes. There is however a fundamental difference between photon and atom optics: While photons do not interact, atom-atom interactions lead to an intrinsic non-linearity in the matter wave dynamics. As these interactions can in principle be controlled (concerning both, sign and magnitude), this adds a powerful degree of freedom to explore new physics regimes, fundamentally inaccessible to photon optics. The tunability of atom interactions is however not yet fully exploited in matter wave optics. The aim of the iWave project is to establish matter wave optics with tunable atom interactions to realize a new class of experiments that go beyond the photon analogy. In particular, we aim to fully exploit the many-particle coherence, correlations, and entanglement of Bose-Einstein condensates in interferometry experiments for fundamental investigations and metrology applications at the quantum limit. The overarching problem with current BEC interferometers is that they are built from atoms with fixed (usually repulsive) interactions. This leads to fundamental phase diffusion, severely limiting the operation time of the interferometer. As a consequence, no metrological relevant device has yet been demonstrated. In iWave we will work to overcome this roadblock by bringing together different experimental techniques in an interdisciplinary approach. In practice we will realize matter wave optics using Cesium atoms, where atom interactions can be dynamically adjusted. This should allow us to extend the interferometer operation time beyond what is accessible in other approaches and reach new regimes of sensitivity. The setup we propose is designed to measure feeble tilts of the line of gravity (tiltmeter). The line of gravity exhibits interesting dynamics on different timescales due to tides, celestial mechanics, processes of the earths interior and several others. We will collaborate with the geodesy department to analyze and interpret the observed signals.

In the framework of the iWave project, a new experimental setup for the generation and study of ultra cold and quantum-degenerate gases of Caesium was constructed. This setup combines the established methods of atom chips with optical dipole trapping, it is the first setup of its kind. This combination allows trapping and manipulation of Caesium atoms in arbitrary hyperfine and Zeeman states in close proximity to the atom chip wires and hence realize strong local near fields in the radio frequency and microwave regime. Direkt optical access is enabled through a through-chip window. At the end of the project, the setup is fully functioning, routinely producing cold trapped samples (cycle time 5 s) in controlled states. Current studies investigate the collisional properties, most notably Feshbach resonances, as a function of density, temperature, dc magnetic field, state (mixture). Evaporative Cooling is effective in the 3-3 (and 4-4) state, realization of a BEC is pending. Due to the CORONA pandemic, the progress is delayed with respect to the original planning, partially because of limited (or no) access to the lab, partially due to massivley enhanced delivery times of components. Project phase 3 (out of 5) could be finished successfully. The experimental setup is working beautifully, the future investigations will be carried out in the framework of a bi-national FWF-ANR follow-up project "Microwave and Radiofrequency control of cold alkali atoms collisions" in collaboration with Aurelien Perrin from Université Paris Nord, with support by Jean Dalibard and Timur Tscherbul.