Competition between Spin Echo and Spin Self-Rephasing in a Trapped Atom   Interferometer
  We perform Ramsey interferometry on an ultracold 87Rb ensemble confined in an optical dipoletrap. We use a \pi-pulse set at the middle of the interferometer to restore the coherence of the spinensemble by canceling out phase inhomogeneities and creating a spin echo in the contrast. However,for high atomic densities, we observe the opposite behavior: the \pi-pulse accelerates the dephasingof the spin ensemble leading to a faster contrast decay of the interferometer. We understand thisphenomenon as a competition between the spin-echo technique and an exchange-interaction drivenspin self-rephasing mechanism based on the identical spin rotation effect. Our experimental data iswell reproduced by a numerical model. 
Cyrille Solaro (LNE - SYRTE), Alexis Bonnin (LNE - SYRTE),   Fr\'ed\'eric Combes (LPS), Matthias Lopez (LNE - SYRTE), Xavier...
physics.atom-ph cond-mat.quant-gas