We propose a method to create superpositions of two macroscopic quantum states of a single-mode microwave cavity field interacting with a superconducting charge qubit. The decoherence of such superpositions can be determined by measuring either the Wigner function of the cavity field or the charge qubit states. Then the quality factor Q of the cavity can be inferred from the decoherence of the superposed states. The proposed method is experimentally realizable within current technology even when the Q value is relatively low, and the interaction between the qubit and the cavity field is weak.
@article{arxiv.quant-ph/0506016,
title = {Measuring the quality factor of a microwave cavity using superconduting qubit devices},
author = {Yu-xi Liu and L. F. Wei and Franco Nori},
journal= {arXiv preprint arXiv:quant-ph/0506016},
year = {2009}
}