Paper detail

Irreversibility of decorrelating processes: an experimental assessment in cavity QED

Entropy production quantifies the amount of irreversibility of a physical process, leading to fundamental bounds for thermodynamic quantities. Particularly in the quantum realm, considerable research has been carried out in the last decades extending entropy production to nonequilibrium processes. We experimentally investigate the entropy production of forward-backward cycles containing different decorrelating processes realized to erase different types of correlations between two interacting systems, from obliterating solely quantum coherence to completely decorrelating local states. We apply these processes to the entanglement of a two-level atom, realized with a circular Rydberg atom, and a light field of a high-quality microwave cavity. The entropy production is computed from the full quantum-state tomography of the system performed at different stages of the interaction-decorrelation sequence. Due to the quantum nature of the atom-cavity system, we find that, although standard, the maximum likelihood estimation method for the density matrix leads to spurious divergences of the entropy production. We propose and implement an alternative estimator that remedies such divergences. Our work experimentally assesses irreversibility of non-thermal processes and addresses the care that must be taken in handling experimental data to estimate the entropy production.