YBCO-on-Kapton: Material for High-Density Quantum Computer Interconnects with Ultra-Low Thermal Loss

Development of practical quantum computers would require 1000's of qubits and equally large number of read-out, bias and drive lines. New materials that combine low passive loss and good RF properties are needed. Here we report performance of signal interconnects comprised of high-temperature YBCO films that are exfoliated from a metal substrate and transferred to a E-Kapton tape. The technology offers low-loss transition between 60 K to sub-mK environments and interfacing with off-shelf flexible silicon electronics. We demonstrate <1 dB/m attenuation at 6 GHz at 77 K. The microstrip assemblies demonstrated no degradation upon multiple cycling to liquid Nitrogen and conduction cooling down to 18 K. We discuss the design of a practical high-density signal cable with passive loss well below 1 μW per line. The YBCO-on-Kapton technology offers a practical pathway to large error-corrected quantum computing systems.