Seminar
Tuesday, 20 April, 2010
Group Seminar LMU: Spin squeezing and nonlinear interferometry with ultra-cold quantum gases
Tuesday, 20.04.2010 10 a.m. (s.t.) in H107, Fakultät für Physik LMU
Christian Gross, Synthetic Quantum Systems, Kirchhoff Institute for Physics, University of Heidelberg
The optimal phase detection precision of "classical" linear atom interferometers is given by the standard quantum limit. Using spin squeezed states this "classical" limit can be beaten and therefore a greater measurement precision is possible.
We report on the generation of spin squeezed states in two experiments, one based on external and the second based on internal degrees of freedom of a Rubidium Bose-Einstein condensate. In the external case we detect spin squeezing despite of finite temperature, but due to the lack of a beam splitter analog the realization of a complete interferometer is still an open challenge. In the internal case precise control of the collective spin state and thus the realization of a full interferometer is possible. Interaction tuning via a narrow Feshbach resonance is used to generate spin squeezed states dynamically in the interferometer. A prototypal measurement with this nonlinear interferometer shows a phase precision enhancement of 15% beyond the "classical" limit. Characterization of the quantum state within the interferometer reveals spin squeezing of -8.2dB and furthermore entanglement of 170 atoms.