Thermodynamics of non-Hermitian Josephson junctions with exceptional points

We present an analytical formulation of the thermodynamics, free energy, and entropy of any generic Bogoliubov--de Gennes model which develops exceptional point (EP) bifurcations in its complex spectrum when coupled to reservoirs. We apply our formalism to a non-Hermitian Josephson junction where, despite recent claims, the supercurrent does not exhibit any divergences at EPs. The entropy, on the contrary, shows a universal jump of $1/2\phantom{\rule{0.16em}{0ex}}ln2$, which can be linked to the emergence of Majorana zero modes at EPs. Our method allows us to obtain precise analytical boundaries for the temperatures at which such Majorana entropy steps appear. We propose a generalized Maxwell relation linking supercurrents and entropy which could pave the way towards the direct experimental observation of such steps in, e.g., quantum-dot-based minimal Kitaev chains.