Spontaneous spin squeezing in a rubidium BEC

Abstract

We describe an experiment where spin squeezing occurs spontaneously within a\nstandard Ramsey sequence driving a two-component Bose-Einstein condensate (BEC)\nof 87Rb atoms trapped in an elongated magnetic trap. Multiparticle entanglement\nis generated by state-dependent collisional interactions, despite the\nnear-identical scattering lengths of the spin states in 87Rb. In our\nproof-of-principle experiment, we observe a metrological spin squeezing that\nreaches 1.3+/-0.4dB for 5000 atoms, with a contrast of 90+/-1%. The method may\nbe applied to realize spin-squeezed BEC sources for atom interferometry without\nthe need for cavities, state-dependent potentials or Feshbach resonances.\n