  We introduce and experimentally characterize a general purpose device for
signal processing in circuit quantum electrodynamics systems. The device is a
broadband two-port microwave circuit element with three modes of operation: it
can transmit, reflect, or invert incident signals between 4 and 8 GHz. This
property makes it a versatile tool for lossless signal processing at cryogenic
temperatures. In particular, rapid switching (less than or equal to 15 ns)
between these operation modes enables several multiplexing readout protocols
for superconducting qubits. We report the device's performance in a two-channel
code domain multiplexing demonstration. The multiplexed data are recovered with
fast readout times (up to 400 ns) and infidelities less than 0.01 for probe
powers greater than 7 fW, in agreement with the expectation for binary
signaling with Gaussian noise.
