Pair Correlations in Atomic Bose Gases

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Pair correlations play a central role in the physics of interacting quantum gases. In atomic Bose and Fermi gases they can be varied over many orders of magnitude with the help of Feshbach resonances. This control is used in a variety of ways in current research and makes the field of atomic quantum gases extremely fruitful for a deeper understanding of quantum many-body systems.Until now, pair correlations could only be observed via the increased inelastic scattering losses associated with them. This method is very time-consuming, since for each data point a complete experimental cycle of several tens of seconds must be run through. The recording of meaningful spectra therefore requires several days to weeks. Last year, we developed a method that overcomes these problems and allows us to observe pair correlations in situ with a time resolution of less than 100 nanoseconds without destroying the atomic quantum gas. With the present proposal we want to further develop the method and apply it to two fundamental questions. The first issue concerns unitary Bose gases. Unitary Bose gases are quantum gases with maximum pair correlation at small distances. They are universal many-body systems whose properties depend only on the mass of the atoms and the particle density. Due to their fundamental importance, they are currently the subject of intensive experimental and theoretical research. We plan to use our method to study the dynamic properties of unitary Bose gases. For this purpose, the scattering length is periodically modulated and the change of the pair correlation observable directly in the ion signal is detected in situ and with high time resolution. In a second subproject we plan to use our method to detect Efimov trimers. In our Tübingen lithium-rubidium mixture we have investigated bound heteronuclear Efimov trimer states. Here, too, we were previously dependent on the extremely time-consuming and noisy observation of three-body losses. Efimov states consisting of one light atom (lithium) and two heavy atoms (rubidium) can be attributed to a two-body problem by adiabatically eliminating the fast dynamics of the light atom. This leads to an additional potential between the two heavy atoms. The resulting change in the pair correlation of the heavy atoms should be observable in the ion signal in situ and in real time.