Abstract: An I/O system and device for use with superconducting device provides multi-stage filtering using superconducting electrical pathways, while providing good thermal conductivity to maintain low temperature of the various components and allowing the easy mounting and dismounting of a device sample from a refrigerated environment. Filtering may include a lumped element filter assembly including multiple plates each carrying a number of lumped element filters. Filtering may include a metal powder filter assembly including multiple metal power filters formed in passages of a substantially non-magnetic portions. A device sample holder assembly secures a device sample, for example a superconducting quantum processor, and provides signals, ground and good thermal conduction.