  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. Here 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.
