EUROCORES_EUROQUASAR_1.Call_QuDeGPM_quantum-Degenerate Gases for Precision Measurements

Atom interference has been applied in many pioneering experiments ranging from fundamental studies to precision measurements. The techniques of laser cooling and trapping have allowed the realization of bright sources of macroscopic matter waves. The central goal of the Collaborative Research Project QuDeGPM is to build on this expertise and use interference of quantum degenerate macroscopic matter waves for a new generation of precision measurements. Two sets of applications are envisioned: (1) Precision determination of fundamental constants and inertial forces in free space, and (2) Interferometers for trapped atoms close to the surface as a microscope for highly sensitive measurements of surface forces on m length scale. To achieve the ultimate sensitivity we will engineer the interactions between the atoms and create non-classical matter-wave quantum states to beat the standard quantum measurement limit. Ultracold degenerate quantum gases with their inherent coherence and narrow spread in space and momentum promise to be the ideal starting point for precision matter wave interference experiments, similar to lasers for light optics. In contrast to light, atoms interact with each other, and the physics of degenerate quantum gases is in many cases dominated by these interactions. This can be an advantage, allowing tricks from non-linear optics like squeezing to boost sensitivity, and a disadvantage, resulting in additional dephasing due to uncontrolled collisional phase shifts. We will exploit recent advances in controlling these interactions by Feshbach resonances to pick out the advantages and to suppress the disadvantages caused by the interactions. The project is organized along the main objectives of (i) performing precision atom interferometry with quantum degenerate gases, (ii) using quantum degenerate gases for precision surface probing, and (iii) exploring, realizing, and testing novel measurement schemes with non-classical matter wave states.

Cold clouds of neutral gases containing a few thousands to a few million atoms and cooled down to a few billionths of degrees above absolute zero (-273.15C) may one day replace lasers in precision measurement devices. Atom interference has already been applied in many pioneering experiments ranging from fundamental studies to precision measurements. The central goal of our research in the framework of the Collaborative Research Project QuDeGPM was to develop an interferometer for trapped atoms to study potentials close to surfaces. An interferometer for trapped atoms consists of a beam splitter which separates a single cloud into two, a measurement time where the coherently split cloud is held and the interaction can shift the phase between the two trapped atomic ensembles. Finally the two clouds are recombined and the relative phase is read by observing the interference. The core of our research project was to investigate each of these steps and implement them on an atom chip, a micro-engineered integrated device used to manipulate the atom clouds. We started by developing a novel detector for atoms that allows is to count every single atom in a time of flight experiment. We then studied experimentally the intrinsic coherence properties of ultracold Bose-Einstein condensates (BEC). This proved that for the elongated clouds we will use for the interferometer they possess coherence properties similar to those of lasers, but their multi mode character, which most probably stems from the interaction between the atoms, persists down to colder temperatures then expected. We then investigated the splitting process itself, both theoretically and in experiment. Using optimal control techniques we studied the splitting protocols with the focus on best interferometer performance. In experiment we were able to demonstrate number squeezing during splitting, a prerequisite to improve interferometer performance. This led to the development of a fully integrated Mach-Zehnder interferometer using a 1d BEC. The performance of the trapped atom interferometer should allow significantly more sensitive measurements of surface potentials as compared to our previous magnetic field microscope experiments. In a parallel study we investigated the intrinsic de-phasing effects which limits the phase accumulation time in an interferometer. Interestingly the system does not decay to the expected thermal equilibrium but to a pre-thermalized state.