This work describes a basic interface between solid-state quantum bits (qubits) and classical environments. We describe a multiplexer, a circulator, and a low noise amplifier, designed for cryogenic temperature operation in a 40 nm CMOS technology node. The circuits take advantage of traditional design styles, such as transmission gates, passive LC filters and switches, and recent developments, such as differential noise cancelling with six-port transformers, while exploiting new cryogenic CMOS (cryo-CMOS) modeling for design and verification purposes.