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 nonadiabatic response when the microwave photon energy hf is comparable to the Kondo temperature k_BT_K. We show that our measurements are qualitatively consistent with the predictions for the radiation-induced decoherence rate of the Kondo spin.