In a superconducting quantum point contact, dynamics of the superconducting phase is coupled to the transitions between the subgap states. We compute this coupling and derive the two-level Hamiltonian of the contact.
@article{arxiv.cond-mat/9808029,
title = {Two-level Hamiltonian of a superconducting quantum point contact},
author = {D. A. Ivanov and M. V. Feigel'man},
journal= {arXiv preprint arXiv:cond-mat/9808029},
year = {2009}
}