A brief introduction to fluctuation theorems: from theory to experiments

Thermodynamics is a fundamental branch of physics, and over the years, it has evolved to include mesoscopic and out-of-equilibrium systems driven by theoretical and experimental advances at the micro- and nanoscale. This development has led to stochastic thermodynamics, a framework that connects microscopic fluctuations with macroscopic laws. Despite their significance, fundamental ideas, such as fluctuation theorems, are frequently not covered in current curricula, leaving them largely unknown across many disciplines. Here, we present the core results of stochastic thermodynamics, particularly the Jarzynski equality and the Crooks theorem, using an integrated approach combining theoretical foundations with experimental verification using optical tweezers. This approach helps to clarify the fundamentals, linking theoretical ideas to real elements in the lab, showing the simplicity of the apparatus, and presenting detailed procedures for calibration and calculation of relevant quantities to enable the implementation of these experiments in new research and teaching laboratories. The goal is to enrich thermodynamics education and to stimulate exploration in this evolving field.