Superradiance phase transition in the presence of parameter fluctuations

Abstract: We theoretically analyze the effect of parameter fluctuations on the superradiance phase transition in a setup where a large number of superconducting qubits are coupled to a single cavity. We include parameter fluctuations that are typical of superconducting architectures, such as fluctuations in qubit gaps, bias points and qubit-cavity coupling strengths. We find that the phase transition should occur in this case, although it manifests itself somewhat differently from the case with no fluctuations. We also find that fluctuations in the qubit gaps and qubit-cavity coupling strengths do not necessarily make it more difficult to reach the transition point. Fluctuations in the bias points, however, increase the coupling strength required to reach the quantum phase transition point and enter the superradiant phase. Similarly, these fluctuations lower the critical temperature for the thermal phase transition.