Optical spin conductivity in ultracold quantum gases

We show that the optical spin conductivity being a small AC response of bulk current and elusive in condensed matter systems can be measured ultracold atoms. demonstrate this contains rich information on quantum states by analyzing experimentally achievable such as spin-1/2 superfluid Fermi gas, spin-1 Bose-Einstein condensate, Tomonaga-Luttinger liquid. The obtained spectra absent Drude reflect quasiparticle excitations non-Fermi liquid properties. Accessible physical quantities include gap contact for gapped gapless well depletion part parameter cold-atom experiments. Unlike its mass transport counterpart, serves probe applicable to clean atomic gases without disorder lattice potentials. Our formalism generalized various spin-orbit coupled nonequilibrium systems.