Coupled quantum pendula as a possible model for Josephson-junction-based axion detection

The model of two coupled quantum pendula is studied and its suitability to describe Josephson junctions interacting with axions is analysed. It is shown that some physical features of one pendulum, not directly accessible, can be deduced by local measures on the other one, which is experimentally available. Such an effect can be exploited for the axion (the invisible pendulum) detection based on Josephson junctions (the accessible pendulum). The interaction between axion and Josephson junction can be enhanced at the resonance, if the axion and the junction frequencies match, and if the accessible system is prepared in the most convenient initial quantum state.