Moment generating function bound from detailed fluctuation theorem

Abstract

A famous consequence of the detailed fluctuation theorem (FT), $p(\Sigma)/p(-\Sigma)=\exp{(\Sigma)}$, is the integral FT $\langle \exp(-\Sigma)\rangle =1$ for a random variable $\Sigma$ and a distribution $p(\Sigma)$. When $\Sigma$ represents the entropy production in thermodynamics, the main outcome of the integral FT is the second law, $\langle \Sigma \rangle \geq 0$. However, a full description of the fluctuations of $\Sigma$ might require knowledge of the moment generating function (MGF), $G(\alpha):=\langle \exp(\alpha \Sigma) \rangle$. In the context of the detailed FT, we show the MGF is lower bounded in the form $G(\alpha)\geq B(\alpha,\langle\Sigma\rangle)$ for a given mean $\langle\Sigma\rangle$. As applications, we verify that the bound is satisfied for the entropy produced in the heat exchange problem between two reservoirs mediated by a weakly coupled bosonic mode and a qubit swap engine.