We introduce and experimentally characterize a general purpose device forsignal processing in circuit quantum electrodynamics systems. The device is abroadband two-port microwave circuit element with three modes of operation: itcan transmit, reflect, or invert incident signals between 4 and 8 GHz. Thisproperty makes it a versatile tool for lossless signal processing at cryogenictemperatures. In particular, rapid switching (less than or equal to 15 ns)between these operation modes enables several multiplexing readout protocolsfor superconducting qubits. We report the device's performance in a two-channelcode domain multiplexing demonstration. The multiplexed data are recovered withfast readout times (up to 400 ns) and infidelities less than 0.01 for probepowers greater than 7 fW, in agreement with the expectation for binarysignaling with Gaussian noise.
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