The experimental platform of ultracold gases allow for the exploration of new regimes in quantum metrology as well as the demonstration of basic quantum field theoretical phenomena such as Lamb shift in reduced dimension. After giving a short general overview of our activities I will report in detail on two recent experiments which will touch on both aspects.
For the metrological aspect I will discuss our recent results using time reversal of nonlinear many particle dynamics to beat the quantum limited readout of a phase measurement. This is directly connected to the active atom interferometer scheme known as SU(1,1) interferometry .
The analog quantum simulation aspect I will motivate by our recent result on the observation of the phononic Lamb shift for bound polarons. A phenomenon predicted in the context of solid state physics in the early 60ies of last century but could not been observed in a clear direct manner. The atomic system of Bose-Fermi mixture allow for a very clean demonstration of this phenomenon relying on very sensitive spectroscopy building on motional Ramsey spectroscopy . Our results point towards the direction of analog quantum simulators for QED analog phenomenon in reduced dimensions .
 Quantum-enhanced sensing based on time reversal of non-linear dynamics, D. Linnemann et al. PRL 117, 013001 (2016)
 Motional Coherence of Fermions Immersed in a Bose Gas, R. Scelle, et al. Phys.Rev.Lett. 111, 070401 (2013).
 Observation of the Phononic Lamb Shift with a Synthetic Vacuum, T. Rentrop et al. to appear in PRX (2016)