Abstract
We describe an experiment where spin squeezing occurs spontaneously within a standard Ramsey sequence driving a two-component Bose–Einstein condensate (BEC) of 87Rb atoms trapped in an elongated magnetic trap. The squeezing is generated by state-dependent collisional interactions, despite the near-identical scattering lengths of the spin states in 87Rb. In our proof-of-principle experiment, we observe a metrological spin squeezing that reaches 1.3 ± 0.4 dB for 5000 atoms, with a contrast of 90 ± 1%. The method may be applied to realize spin-squeezed BEC sources for atom interferometry without the need for cavities, state-dependent potentials or Feshbach resonances.
Highlights
Bose-Einstein condensates (BECs) of atoms with more than one spin state present rich dynamics in their spin and motional degrees of freedom
Spin-squeezed states of BECs have met with wide interest, and it has been pointed out early on that such states can naturally arise in two-component BECs due to different scattering lengths between the internal states [12]
The basic idea of creating spin squeezing by atomic interaction in a BEC, as originally envisaged in 2001 [12], is understood in the basis of well-defined atom numbers |N1 and |N2 =|N − N1, where the index refers to the spin state and N is the total atom number, which we consider fixed for
Summary
Bose-Einstein condensates (BECs) of atoms with more than one spin state present rich dynamics in their spin and motional degrees of freedom. One class of experiments prepares each atom in the BEC in a precisely controlled spin superposition and explores the complex spatial phase dynamics that deploys due to the spin-dependent interactions [1]. In these studies, mainly focused on the mean field dynamics, the spin state remains unchanged throughout the evolution. Experiments with two-component BECs have not produced such states, except when atomic interactions were enhanced with the help of a Feshbach resonance [3] or by actively separating the spin components in a state-dependent trap [4] Both methods have led to spectacular results, but come at the price of a considerably more complex setup. We describe an experiment where spin squeezing occurs spontaneously after an internal state quench, the dynamics being initiated by an initial π/2 pulse [13] applied to a rubidium BEC in a harmonic trap
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