High-temperature superconducting interconnects for ultra-low temperature, high-field environments

Quantum Information Systems (QIS) can potentially enable breakthroughs in computation science, cryptography, high-resolution spectroscopy for high-energy physics applications and materials science. It is recognized that transmitting large amount of data, such as particle detector readouts or quantum processor information requires new materials that combine low RF loss with low thermal conductivity. Using traditional materials for the interconnects would introduce thermal losses well beyond the capacity of modern cryo-systems. Moreover, new interconnect materials are needed for high magnetic field environments, such as particle detector signal lines. The proposed solution is to use crystalline films of a well-known HTS compound, YBCO, that are exfoliated from the substrate on which they are epitaxially grown and then are transferred to a low-loss dielectric substrate, such as E-Kapton. The thermal loss per a strip-line is thus reduced by a factor of 100 compared to a standard Cupro-Nickel coax line, from 170 Wcm /K to 0.3 Wcm/K, when operating in 1 K – mK gradient, thus enabling multiple readouts with negligible thermal load on the dilution stage. Unlike Nb, HTS materials retain superconductivity in extremely high magnetic field, over 100 T at 4 K. Moreover, recent advances in engineering of correlated nano-structures significantly improved pinning of magnetic flux, especially at low, 5 Tesla, DC field, where the RF loss is dominated by viscous vortex drag. The immediate application of the technology is low-loss readout for The Axion Dark Matter Experiment. The Phase I work will be carried out in collaboration with Fermi National Accelerator Laboratory (FNAL). During the Phase I effort the BTG team will evaluate properties of epitaxial 1 m thick YBCO layers transferred onto 5 mil (0.12 mm) E-Kapton. The FNAL team will assist in designing a resonator structure that is tuned to the frequency of interest, specifically to the mass of axion particle in the future upgrade of the Axion Dark Matter Experiment. The resonators will allow evaluating intrinsic loss of the superconductor in the relevant environment, which will also include a DC magnetic field of variable orientation. Phase II effort will focus on scale up and commercialization of the technology. Besides the quantum detector markets, the material is very for application in data transfer for quantum computer systems. The proposed interconnects would enable future error-corrected quantum computer systems.