Microwave Down-Conversion with an Impedance-Matched $\Lambda$ System in   Driven Circuit QED
  By driving a dispersively coupled qubit-resonator system, we realize an "impedance-matched" $\Lambda$ system that has two identical radiative decay rates from the top level and interacts with a semi-infinite waveguide. It has been predicted that a photon input from the waveguide deterministically induces a Raman transition in the system and switches its electronic state. We confirm this through microwave response to a continuous probe field, observing near-perfect ($99.7\%$) extinction of the reflection and highly efficient ($74\%$) frequency down-conversion. These proof-of-principle results lead to deterministic quantum gates between material qubits and microwave photons and open the possibility for scalable quantum networks interconnected with waveguide photons. 
K. Inomata, K. Koshino, Z. R. Lin, W. D. Oliver, J. S. Tsai, Y.   Nakamura, and T. Yamamoto
quant-ph cond-mat.supr-con physics.atom-ph