  Quantum physics predicts that there is a fundamental maximum heat conductance
across a single transport channel, and that this thermal conductance quantum
$G_Q$ is universal, independent of the type of particles carrying the heat.
Such universality, combined with the relationship between heat and information,
signals a general limit on information transfer. We report on the quantitative
measurement of the quantum limited heat flow for Fermi particles across a
single electronic channel, using noise thermometry. The demonstrated agreement
with the predicted $G_Q$ establishes experimentally this basic building block
of quantum thermal transport. The achieved accuracy of below 10\% opens access
to many experiments involving the quantum manipulation of heat.
