This paper presents the first experimental realization of a superconducting circuit quantum electrodynamics (QED) system in the ultrastrong coupling regime, where the atom-cavity coupling rate $ g $ exceeds the cavity transition frequency $ \omega_r $ by more than 10%. The study demonstrates direct evidence for the breakdown of the Jaynes-Cummings model, which describes the coherent exchange of a single excitation between the atom and the cavity mode. The experiment uses a superconducting flux qubit coupled to a transmission line resonator via a Josephson junction with large nonlinear inductance, achieving a normalized coupling rate $ g/\omega_r $ of up to 12%. The results show that the counterrotating terms in the Hamiltonian become significant in this regime, leading to novel quantum phenomena. The system exhibits anticrossings in the transmission spectra, which are attributed to the simultaneous creation and annihilation of excitations in the qubit and resonator modes. These findings provide experimental confirmation of physics beyond the Jaynes-Cummings model. The study also highlights the potential of superconducting circuit QED for exploring ultrastrong light-matter interactions, with future applications in quantum information processing, squeezing, and causality effects in quantum field theory. The results are in excellent agreement with theoretical predictions and demonstrate the feasibility of achieving ultrastrong coupling in circuit QED systems.This paper presents the first experimental realization of a superconducting circuit quantum electrodynamics (QED) system in the ultrastrong coupling regime, where the atom-cavity coupling rate $ g $ exceeds the cavity transition frequency $ \omega_r $ by more than 10%. The study demonstrates direct evidence for the breakdown of the Jaynes-Cummings model, which describes the coherent exchange of a single excitation between the atom and the cavity mode. The experiment uses a superconducting flux qubit coupled to a transmission line resonator via a Josephson junction with large nonlinear inductance, achieving a normalized coupling rate $ g/\omega_r $ of up to 12%. The results show that the counterrotating terms in the Hamiltonian become significant in this regime, leading to novel quantum phenomena. The system exhibits anticrossings in the transmission spectra, which are attributed to the simultaneous creation and annihilation of excitations in the qubit and resonator modes. These findings provide experimental confirmation of physics beyond the Jaynes-Cummings model. The study also highlights the potential of superconducting circuit QED for exploring ultrastrong light-matter interactions, with future applications in quantum information processing, squeezing, and causality effects in quantum field theory. The results are in excellent agreement with theoretical predictions and demonstrate the feasibility of achieving ultrastrong coupling in circuit QED systems.