Recently, superconducting artificial atom has been justified experimentally as an ideal element for various applications including circuit quantum electrodynamics realizing strong-coupling limit. Some of the proposed systems in this area are usually described in terms of the quantum anharmonic oscillator and display quantum dynamics in macroscopic level, giant nonlinearity as well as very strong coupling with external field and strong coupling with an environment. In this report, we investigate the quantum properties of an artificial atom as a model of multilevel anharmonic oscillator in the framework of photon number distributions as well as the Wigner functions. We concentrate on the regimes of strong driving and giant nonlinearity that allow us to consider artificial atom on the level of few excitation numbers.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.