Multi-component quantum gases: Entanglement and Phononic Lamb shift

Mixtures of quantum gases have been investigated in many different contexts. Here I will present recent results addressing two distinct topics. In the context of spinor condensates I will describe the realization of an atomic SU(1,1) interferometer \footnote{D. Linnemann et al.~ \textbf{Phys.Rev.Lett} 117, 013001 (2016)}. With these experiments we show that time reversal of nonlinear dynamics can be used to utilize many particle entanglement at the Heisenberg limit even in the limit of a noisy atom detector. This opens an alternative route for accessing quantum resources even with limited detection capabilities. As second topic I will report on the first observation of the phononic Lamb shift. It has been predicted in the context of the Fr\" ohlich hamiltonian which describes a particle coupling to excitations of a bosonic system. For the realization we use trapped lithium atoms immersed in a sodium Bose Einstein condensate forming the synthetic vacuum. A precise determination of the self energies with motional Ramsey spectroscopy reveal additional energy shifts to the expected mass renormalization \footnote{T. Rentrop, et al.~ \textbf{Phys.Rev.X} 6, 041041 (2016)}. The minute energyshifts become accessible since the atomic model system allows the direct comparison between quantum vacuum and truely empty space.