Quantum dynamics of a spin-1 condensate in a double-well potential

We study quantum dynamics of a Bose-Einstein condensate of spin-1 atoms inside a double-well potential. Under the single spatial mode approximation for condensate wave functions localized within each of the two wells, we examine quantum entanglement and pseudo-spin-squeezing properties in both the Rabi and Josephson regimes. Quantum fluctuations is found to be more stable leading to robust multipartite entanglement in the lower end of the Josephson regime, or the mean field self-trapped region. Substantial multipartite entanglement is witnessed not only due to pseudo-spin-squeezing by the axis-twisting interaction but also from redistribution of mode-entangled atoms between the wells by the tunneling coupling.