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Long-lived states with well-defined spins in spin-$1/2$ homogeneous Bose gases

Many-body eigenfunctions of the total spin operator can be constructed from the spin and spatial wavefunctions with non-trivial permutation symmetries. Spin-dependent interactions can lead to relaxation of the spin eigenstates to the thermal equilibrium. A mechanism that stabilizes the many-body entangled states is proposed here. Surprisingly, in spite coupling with the chaotic motion of the spatial degrees of freedom, the spin relaxation can be suppressed by destructive quantum interference due to spherical vector and tensor terms of the spin-dependent interactions. Tuning the scattering lengths by the method of Feshbach resonances, readily available in cold atomic labs, can enhance the relaxation timescales by several orders of magnitude.