  We introduce a new paradigm: the chiral electromagnetic local density of
states (LDOS) in a spiral plasmonic nanostructure. In both classical and
quantum regimes, we reveal using scanning near-field optical microscopy (NSOM)
in combination with spin analysis that a spiral cavity possesses spin-dependent
local optical modes. We expect this work to lead to promising directions for
future quantum plasmonic device development, highlighting the potentials of
chirality in quantum information processing.
