  Electromagnetic quantities such as energy density, momentum, spin, and
helicity bring meaning and intuition to electromagnetism and possess intricate
interrelations, particularly prominent in complex non-paraxial near-fields.
These quantities are conventionally expressed using electric and magnetic field
vectors, yet the electric-magnetic basis is one among other often overlooked
alternatives, including parallel-antiparallel and right-left-handed helicity
bases, related to the parity and duality symmetries of electromagnetism.
Projecting time-harmonic electromagnetic fields into a variety of bases allows
re-interpreting established quantities and reveals underlying mathematical
structures: a Bloch sphere which describes asymmetries in electromagnetic
energy, a systematic path to unify and uncover relations between
electromagnetic quantities, and the unlocking of symmetry-driven equations in
light-matter interaction.
