The current emission noise of a carbon nanotube quantum dot in the Kondo regime is measured at frequencies $ u$ of the order or higher than the frequency associated with the Kondo effect $k_B T_K/h$, with $T_K$ the Kondo temperature. The carbon nanotube is coupled via an on-chip resonant circuit to a quantum noise detector, a superconductor-insulator-superconductor junction. We find for $h u approx k_B T_K$ a Kondo effect related singularity at a voltage bias $eV approx h u $, and a strong reduction of this singularity for $h u approx 3 k_B T_K$, in good agreement with theory. Our experiment constitutes a new original tool for the investigation of the non-equilibrium dynamics of many-body phenomena in nanoscale devices.
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