We report the observation of strongly ferromagnetic F = 1 spinor Bose-Einstein condensates of 7 Li atoms. The condensates are generated in an optical dipole trap without using magnetic Feshbach resonances, so that the condensates have internal spin degrees of freedom. Studying the nonequilibrium spin dynamics, we have measured the ferromagnetic spin interaction energy and determined the s-wave scattering length difference among total spin f channels to be a f =2 − a f =0 = −18(3) Bohr radius. This strong collision-channel dependence leads to a large variation in the condensate size with different spin composition. We were able to excite a radial monopole mode after a spin-flip transition between the |m F = 0 and |m F = 1 spin states. From the experiments, we estimated the scattering length ratio a f =2 /a f =0 = 0.27(6), and determined a f =2 = 7(2) and a f =0 = 25(5) Bohr radii, respectively. The results indicate the spin-dependent interaction energy of our system is as large as 46% of the condensate chemical potential.

We demonstrate the production of large 7 Li Bose-Einstein condensates in an optical dipole trap using D1 gray molasses. The sub-Doppler cooling technique reduces the temperature of 4×10 9 atoms to 25 µK in 3 ms. After microwave evaporation cooling in a magnetic quadrupole trap, we transfer the atoms to a crossed optical dipole trap, where we employ a magnetic Feshbach resonance on the |F = 1, mF = 1 state. Fast evaporation cooling is achieved by tilting the optical potential using a magnetic field gradient on the top of the Feshbach field. Our setup produces pure condensates with 2.7×10 6 atoms in the optical potential for every 11 s. The trap tilt evaporation allows rapid thermal quench, and spontaneous vortices are observed in the condensates as a result of the Kibble-Zurek mechanism.

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We report the observation of matter-wave jet emission in a strongly ferromagnetic spinor Bose-Einstein condensate of 7 Li atoms. Directional atomic beams with |F = 1, m F = 1 and |F = 1, m F = −1 spin states are generated from |F = 1, m F = 0 state condensates, or vice versa. This results from collective spin-mixing scattering events, where spontaneously produced pairs of atoms with opposite momentum facilitates additional spin-mixing collisions as they pass through the condensates. The matter-wave jets of different spin states (|F = 1, m F = ±1 ) can be a macroscopic Einstein-Podolsky-Rosen state with spacelike separation. Its spinmomentum correlations are studied by using the angular correlation function for each spin state. Rotating the spin axis, the inter-spin and intra-spin momentum correlation peaks display a high contrast oscillation, indicating collective coherence of the atomic ensembles. We provide numerical calculations that describe the experimental results at a quantitative level and can identify its entanglement after 100 ms of a long time-of-flight.

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