It has been shown that there are not only transverse but also longitudinal couplings between microwave fields and a superconducting qubit with broken inversion symmetry of the potential energy. Using multiphoton processes induced by longitudinal coupling fields and frequency matching conditions, we design a universal algorithm to produce arbitrary superpositions of two-mode photon states of microwave fields in two separated transmission line resonators, which are coupled to a superconducting qubit. Based on our algorithm, we analyze the generation of evenly-populated states and NOON states. Compared to other proposals with only single-photon process, we provide an efficient way to produce entangled microwave states when the interactions between superconducting qubits and microwave fields are in the ultrastrong regime.
@article{arxiv.1506.06363,
title = {Engineering entangled microwave photon states via multiphoton interactions between two cavity fields and a superconducting qubit},
author = {Yan-Jun Zhao and Chang-Qing Wang and Xiaobo Zhu and Yu-xi Liu},
journal= {arXiv preprint arXiv:1506.06363},
year = {2016}
}