Fluctuations of entropy production in partially masked electric circuits

We experimentally investigate fluctuations of entropy production in a coupled driven-RC circuit. In particular, we focus on the hidden-variable problem, where part of the circuit is neglected intentionally. In the two versions of the reduced descriptions we provide for the system, the fluctuation theorem (FT) is valid in all timescales for weak coupling. However, FT fails in the strong-coupling regime, in the short-time limit for one version, and in the long-time limit for the other. In these timescales where FT fails, both descriptions still give FT-like behavior. The failure of FT implies non-Markovian dynamics, meaning there exists a hidden variable that cannot be incorporated into the heat bath. We argue that FT can be restored with the introduction of a timescale-dependent effective noise.