  We present measurements of current noise in quantum point contacts as a
function of source-drain bias, gate voltage, and in-plane magnetic field. At
zero bias, Johnson noise provides a measure of the electron temperature. At
finite bias, shot noise at zero field exhibits an asymmetry related to the 0.7
structure in conductance. The asymmetry in noise evolves smoothly into the
symmetric signature of spin-resolved electron transmission at high field.
Comparison to a phenomenological model with density-dependent level splitting
yields quantitative agreement. Additionally, a device-specific contribution to
the finite-bias noise, particularly visible on conductance plateaus (where shot
noise vanishes), agrees quantitatively with a model of bias-dependent electron
heating.
