Pair superfluidity in generalized Bose-Hubbard models

We investigate pair superfluidity in a generalized Bose-Hubbard model, extending the framework to include pair hopping and direct on-site pair interactions. Our study reveals unique features of the pair superfluid phase, such as reentrant behavior and pockets of the normal state within the superfluid region---phenomena absent in single-particle superfluid models. Through compressibility analysis, we identify Mott insulating features at zero temperature and a complex interplay between temperature, chemical potential, and pair hopping. We highlight the importance of the occupation basis size in accurately modeling pair-superfluid dynamics, demonstrating that excessive truncation leads to unphysical artifacts. Additionally, we present phase diagrams contrasting pair and single-particle superfluidity, showing the distinct nature of their respective transitions and phase boundaries. Our findings provide theoretical insights relevant to experimental platforms, such as ultracold atomic gases and Josephson junction systems, and utilize Floquet engineering as a justification for achieving and controlling pair-hopping dynamics. This paper enhances our understanding of pair superfluidity and paves the way for further exploration of complex quantum many-body systems.