Observation of a strongly ferromagnetic spinor Bose-Einstein condensate

Abstract

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.

Three-body spin mixing in spin-1 Bose-Einstein condensates

“…Finally, we note that the exponential growth of N p (t ) below the critical value of q Z in Eq. (37) has recently been observed for a spin-1 BEC of 7 Li atoms [6]. Tuning the magnetic field strength closer to the critical value could also reveal signatures of three-body spin exchange for these atoms.…”

“…The properties of spinor BECs depend crucially on spin-mixing collisions, which change the spin state of the colliding atoms. Such collisions have been observed for several atomic species and spins [4][5][6][7][8][9][10][11].…”

“…Our results for a 0 and a 2 are consistent with the values stated in Refs. [2,6,[40][41][42][43]. We also give r vdW in units of the Bohr radius a B .…”

“…The first spinor BEC consisting of 23 Na atoms featured antiferromagnetic interactions [3,4]. Spinor condensates with ferromagnetic interactions have been created with 87 Rb atoms [5] and recently also with 7 Li atoms [6]. The properties of spinor BECs depend crucially on spin-mixing collisions, which change the spin state of the colliding atoms.…”

Damped point-vortex model for polar-core spin vortices in a ferromagnetic spin-1 Bose-Einstein condensate

“…The spin-1 atoms interact via spin-independent (strength g n ) and spin-dependent (strength g s ) interactions, with n(x) = Ψ † (x)Ψ(x) the areal density and F(x) = µ=x,y,z Ψ † (x)f µ Ψ(x)ŝ µ the areal spin density for spin-1 Pauli matrices f µ and spin directions ŝµ . We consider ferromagnetic (g s < 0) spin interactions, arising for example in 87 Rb [74, 75] and 7 Li [76], which favours a nonzero magnetization density. A magnetic field along ŝz , along with microwave dressing techniques [77,78], results in a Zeeman splitting of the spin levels, and has both a linear p and quadratic q contribution.…”