  Spin transport phenomena at strongly-correlated interfaces play central roles
in fundamental physics as well as spintronic applications. To anatomize
spin-transport carriers, we propose the detection of the spin current noise in
interacting itinerant fermions. The Fano factor given by the ratio between the
spin current and its noise reflects elementary carriers of spin transport at
the interface of spin-polarized Fermi gases realized in ultracold atoms. The
change of the Fano factor microscopically evinces a crossover from the
quasiparticle transport to magnon transport in itinerant fermionic systems.
