Integrating High-Density Microwave Signalling and Packaging With Superconducting Qubits

One of the challenges for building a quantum computer with superconducting qubits is being able to integrate a sufficient density of microwave lines in a cryogenic environment. Traditionally this has been limited by the pitch of SMA cables. When trying to go beyond this approach there are two problems to address. The first is outfitting a dilution refrigerator with enough lines to run from room temperature to the base temperature stage. The second is building a package for a quantum integrated circuit that houses enough microwave lines itself. We propose a solution to both of these problems by using RF flexible circuits to increase signal density in the dilution refrigerator and package while maintaining signal integrity. We also discuss the thermal, mechanical and RF considerations that go into designing such a system. Finally we show a proof-of-concept integration of the entire system including measurements with superconducting qubits.