Microwave-assisted reversal of a single electron spin

The dynamics of a quantum system in a dissipative environment presents a rich and still largely unexplored phenomenology that is relevant for the control of quantum devices. The simplest problem can be modeled as a two-level system—such as a spin—in contact with a thermal bath. Here, we present experiments in which we monitor the spin reversal in a TbPc2 single-molecule spin transistor, and we show that the application of microwave pulses can cause the spin to flip between its two lowest-lying states (|↑⟩ and |↓⟩) at a rate that increases with increasing duration and power of the pulses. This process is neither resonant nor coherent with the microwave pulses. Moreover, an asymmetry appears in the |↓⟩→|↑⟩ and |↑⟩→|↓⟩ transition probabilities, suggesting that the process occurs out of equilibrium. We explain the experimental results and provide an estimate of the local temperature increase induced by the microwave pulses by means of a model that takes into account the energy exchange between the single Tb3+ electron spin and the local environment.