We revisit the harmonic approximation (HA) for a large Josephson junction interacting with some charge qubits through the variational approach for the quantum dynamics of the junction-qubit coupling system. By making use of numerical calculation and analytical treatment, the conditions under which HA works well can be precisely presented to control the parameters implementing the two-qubit quantum logical gate through the couplings to the large junction with harmonic oscillator (HO) Hamiltonian.
@article{arxiv.quant-ph/0409013,
title = {On the Harmonic approximation for large Josephson junction coupling charge qubits},
author = {T. Shi and B. Chen and Z. Song and C. P. Sun},
journal= {arXiv preprint arXiv:quant-ph/0409013},
year = {2015}
}