Connecting electrical circuitry in a quantum computing system

A cryogenic system comprising:

• a plurality of isothermal plates;
• and
• at least one flexible cable comprising:
• a flexible strip with first and second parallel surfaces and first and second ends, the flexible strip being electrically insulating;
• a first metal stripline within the flexible strip;
• first and second metallic grounding planes on the first and second parallel surfaces, respectively;
• and
• a mechanical stiffener material attached to at least an end portion of one of the first and second ends of the flexible cable to at least one of the first and second metallic grounding planes;
• and
• a quantum processing unit electrically connected to the at least one flexible cable at the first end, the quantum processing unit comprising superconducting circuits, wherein the cryogenic system is configured for the flexible cable to carry one or more signals to the quantum processing unit;
• and
• an electrical connector providing electrical connection of the at least one flexible cable and the quantum processing unit.