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 a 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.During the Phase I effort the Brookhaven Technology Group (BTG) team developed a process for the transfer of high-quality epitaxial films on 5 mil (0.12 mm) E-Kapton over a 0.5 m length. The films were used to manufacture 25 col-planar resonator structures and evaluation of intrinsic R.F. loss both at 77 K and 25 K. The coupling strength of the resonators was systematically varied to separate the effects of coupling loss from the intrinsic, conduction, and dielectric loss. The resonators were tested in a magnetic field up to 0.8 Tesla at 25 K. The R.F. properties did not degrade, which indicates that the material is highly suitable for R.F. links in high-field environments. Phase II work will focus on scaling of the technology beyond 0.5 m batch processing. The team will develop economic and efficient methods of reel-to-reel lamination, patterning and drilling. In collaboration with ChemCubed LLC, BTG will employ advanced ink-jet photoresist deposition for patterning the cable structures. For the first time, the project will develop a via technology that is compatible with the YBCO superconductor. The via process will enable the low level of inter-line crosstalk needed for both high- energy and commercial applications. A 2-meter-long YBCO-Kapton cable with projected < 0.1 dB insertion loss and < -60 dB crosstalk will be tested by the Fermilab team in the relevant environment. Besides the high-energy physics quantum detector markets, the material is very suitable for application in data transfer for quantum computer systems. The proposed interconnects would enable future error- corrected quantum computer systems.