Dynamic response of a spin-1/2 Kondo singlet

We present a study of spin 1/2 Kondo singlets in single electron transistors under a microwave frequency bias excitation. We compare time-averaged conductance $G$ to predicted universal response with respect to microwave frequency, oscillation amplitude and the Kondo temperature and find a non-adiabatic response when the microwave photon energy $hf$ is comparable to the Kondo temperature $k_B T_K$. We show that our measurements are qualitatively consistent with the predictions for the radiation-induced decoherence rate of the Kondo spin.