Non-thermal energy fluctuations of a qutrit under feedback-controlled dissipative dynamics

Diamond spins disclose new possibilities for exploring how thermodynamic processes take place in open systems at the nanoscales, where fluctuations play a paramount role, and quantum features show up.

We characterize the energy exchange fluctuations of a diamond spin qutrit in contact with an engineered non-thermal reservoir realized by the interaction with short laser pulses. The spin dynamics is well described as an intrinsic feedback process where dissipation is conditioned by measurement, and –as opposed to two-level systems– produces utterly quantum (non-thermal) out-of-equilibrium steady states. We were able to experimentally verify the validity of the general quantum fluctuation relation in a dissipative scenario, and quantify the efficacy of the measurements and dissipation in opening the system. We also show that this efficacy can be used as a measure of non-unitality of the map.

This represents the first experimental verification of quantum fluctuation relations in an open quantum system under a non-microreversible dynamics.