How do I design a cryogenic microwave switch for routing signals between multiple qubits?

A cryogenic microwave switch for routing signals between multiple qubits must operate at millikelvin temperatures while providing: low insertion loss (< 0.1-0.5 dB, critical for preserving few-photon quantum signals), high isolation (> 20-40 dB between ports, to prevent cross-talk between qubit channels), wideband operation (4-12 GHz to cover qubit and readout frequencies), minimal heat dissipation (< 1-10 microwatts at the mixing chamber stage), and fast switching speed (< 1-100 microseconds for multiplexed measurement or routing). Switch technologies applicable at cryogenic temperatures include: superconducting MEMS switches (micro-machined mechanical switches using superconducting contacts; insertion loss < 0.1 dB, isolation > 30 dB, switching time approximately 1-10 microseconds; the most promising technology for quantum routing but still in research stage), semiconductor switches at the 4 K stage (GaAs or InP HEMT-based switches operated at 4 K; insertion loss 0.5-2 dB, isolation 20-30 dB, switching time < 10 nanoseconds; commercial cryogenic switches from Radiall and others are available but add noise and loss), flux-tunable couplers (superconducting circuits that use a tunable coupler element, often a SQUID, to switch the coupling between two qubits or signal paths on and off; insertion loss < 0.1 dB, isolation 20-40 dB, switching time approximately 10-100 nanoseconds; no moving parts, fully integrated on the qubit chip), and parametric switches (using a nonlinear superconducting element pumped at a specific frequency to activate or deactivate signal routing; all-superconducting, no moving parts).