Stochastic excursions of quantum thermal machines

We will present recent results on the description of thermodynamic fluctuations in quantum trajectories using the concept of stochastic excursions. The problem will be motivated with two examples: cooling of a superconducting qubit using an absorption refrigerator, and quantum sensing using transport across a double quantum dot. We will introduce the concept of stochastic excursions, and show how it can be used to decompose stochastic trajectories into segments with clear physical meanings. We will also show how this formalism can be used to decompose the current noise into specific contributions, which provide key insights into the mechanisms responsible for fluctuations. Finally, we will connect our results to the problem of optimal time estimation using stochastic data.