Microwave Down-Conversion with an Impedance-Matched $\Lambda$ System in Driven Circuit QED

Understand

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.