Multiplexed Readout of Transmon Qubits with Josephson Bifurcation   Amplifiers
  Achieving individual qubit readout is a major challenge in the development of scalable superconducting quantum processors. We have implemented the multiplexed readout of a four transmon qubit circuit using non-linear resonators operated as Josephson bifurcation amplifiers. We demonstrate the simultaneous measurement of Rabi oscillations of the four transmons. We find that multiplexed Josephson bifurcation is a high-fidelity readout method, the scalability of which is not limited by the need of a large bandwidth nearly quantum-limited amplifier as is the case with linear readout resonators. 
V. Schmitt, X. Zhou, K. Juliusson, A. Blais, P. Bertet, D. Vion, and   D. Esteve
quant-ph cond-mat.supr-con