edoc: No conditions. Results ordered -Date Deposited. 2024-11-12T00:33:47ZEPrintshttps://edoc.unibas.ch/images/uni-logo.jpghttps://edoc.unibas.ch/2017-02-15T13:39:30Z2018-11-01T16:21:58Zhttps://edoc.unibas.ch/id/eprint/52751This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/527512017-02-15T13:39:30ZBell correlations in a Bose-Einstein condensateCharacterizing many-body systems through the quantum correlations between their constituent particles is a major goal of quantum physics. Although entanglement is routinely observed in many systems, we report here the detection of stronger correlationsâ€”Bell correlationsâ€”between the spins of about 480 atoms in a Bose-Einstein condensate. We derive a Bell correlation witness from a many-particle Bell inequality involving only one- and two-body correlation functions. Our measurement on a spin-squeezed state exceeds the threshold for Bell correlations by 3.8 standard deviations. Our work shows that the strongest possible nonclassical correlations are experimentally accessible in many-body systems and that they can be revealed by collective measurements. Roman SchmiedJean-Daniel BancalBaptiste AllardMatteo FadelValerio ScaraniPhilipp TreutleinNicolas Sangouard2017-02-15T13:32:05Z2017-02-15T13:32:05Zhttps://edoc.unibas.ch/id/eprint/52750This item is in the repository with the URL: https://edoc.unibas.ch/id/eprint/527502017-02-15T13:32:05ZSideband Rabi spectroscopy of finite-temperature trapped Bose gasesWe use Rabi spectroscopy to explore the low-energy excitation spectrum of a finite-temperature Bose gas of rubidium atoms across the phase transition to a Bose-Einstein condensate (BEC). To record this spectrum, we coherently drive the atomic population between two spin states. A small relative displacement of the spin-specific trapping potentials enables sideband transitions between different motional states. The intrinsic nonlinearity of the motional spectrum, mainly originating from two-body interactions, makes it possible to resolve and address individual excitation lines. Together with sensitive atom counting, this constitutes a feasible technique to count single excited atoms of a BEC and to determine the temperature of nearly pure condensates. As an example, we show that for a nearly pure BEC of N=800 atoms the first excited state has a population of less than five atoms, corresponding to an upper bound on the temperature of 30nK. Baptiste AllardMatteo FadelRoman SchmiedPhilipp Treutlein