  The electron g-factor measured in a quantum point contact by source-drain
bias spectroscopy is significantly larger than its value in a two-dimensional
electron gas. This enhancement, established experimentally in numerous studies,
is an outstanding puzzle. In the present work we explain the mechanism of this
enhancement in a theory accounting for the electron-electron interactions. We
show that the effect relies crucially on the non-equilibrium nature of the
spectroscopy at finite bias.
