SU(N) symmetry can emerge in a quantum system with N single-particle spin states when spin is decoupled from inter-particle interactions. So far, only indirect evidence for this symmetry exists, and the scattering parameters remain largely unknown. H
ere we report the first spectroscopic observation of SU(N=10) symmetry in Sr-87 using the state-of-the-art measurement precision offered by an ultra-stable laser. By encoding the electronic orbital degree of freedom in two clock states, while keeping the system open to 10 nuclear spin sublevels, we probe the non-equilibrium two-orbital SU(N) magnetism via Ramsey spectroscopy of atoms confined in an array of two-dimensional optical traps. We study the spin-orbital quantum dynamics and determine all relevant interaction parameters. This work prepares for using alkaline-earth atoms as test-beds for iconic orbital models.
Two anomalously weak transitions within the $2 ^3{rm S}_1~-~3 ^3{rm P}_J$ manifolds in $^3$He have been identified. Their transition strengths are measured to be 1,000 times weaker than that of the strongest transition in the same group. This dramati
c suppression of transition strengths is due to the dominance of the hyperfine interaction over the fine structure interaction. An alternative selection rule based on textit{IS}-coupling (where the nuclear spin is first coupled to the total electron spin) is proposed. This provides qualitative understanding of the transition strengths. It is shown that the small deviations from the textit{IS}-coupling model are fully accounted for by an exact diagonalization of the strongly interacting states.
