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To address the challenge of dense connectors for cryogenic systems, we describe a face-to-face cable connection approach for connecting microwave superconducting stripline cables. The approach provides a space-efficient and reliable interconnect technology for future cryogenic and quantum technology applications at microwave frequencies. A self-aligned assembly was used and was comprised of bottom and top alignment molybdenum pieces and flexible superconducting stripline cables. SU-8, a photodefinable epoxy-based photoresist, was used to form structures defined on the bottom and top Mo pieces to provide alignment and distribute mechanical pressure in the contact regions of the cables. We measured critical transition temperatures in the range of 8.6-9.0 K and an average critical current of 10.2 mA. Time-domain reflectometry measurements at 4.2 K showed a relatively small impedance discontinuity at the connection point and minimal microwave power dependency was observed. This cable-to-cable connection approach for thin, flexible superconducting cables shows promising results as a solution for dense signal integration for microwave and DC interconnects at cryogenic temperatures. [ABSTRACT FROM AUTHOR]

Flexible superconducting Nb microstrip transmission line cables, with lengths of $\sim$5 cm, were fabricated using 2 mil (50.8  $\mu$m) thick E-series Kapton films. A 50 nm Ti layer was used to improve the adhesion of sputter-deposited 250-nm-thick Nb signal line and ground plane metallization. The signal traces of the microstrip were directly interfaced with edge-launch SMA connectors and measured up to 14 GHz in liquid He. For comparison, we also fabricated normal conductor (Ti/Cu) microstrip transmission lines with a similar design. The microwave performance of the Nb-based transmission lines indicates significantly lower intrinsic insertion loss (less than $\sim$ 0.02 dB/cm) compared to the Cu-based microstrip measured at 4.2 K to have a loss of $\sim$0.57 dB/cm. [ABSTRACT FROM PUBLISHER]