Low-noise superconducting interconnects

The superconducting interconnects for SuperCDMS SNOLAB have a critical need to suppress noise generated both internally and externally. RF noise, both externally and internally, interferes with or degrades signal value going from the mK to room temperature stages, and noise traveling from room temperature stages down to the mK stage contributes to the heat load at the mK stage, where thermal cooling power is small, and thermometry is sensitive. Working with Prof. Mirabolfathi (collaborator in SuperCDMS) as a consultant, we proposal to model, develop and test various line filters that limit external and internal noise signals, including microphonic noise generated from mechanical vibrations of materials that exhibit piezoelectric activity. We propose to make shielded, multi-line, superconducting ribbon cable on Kapton that includes noisemitigating components. In Phase II, we plan to print superconducting layers on printed copper or silver signal wires to achieve continuous ribbon cable from mK to room temperature, eliminating the need to make intermediate connectors that could introduce noise in the circuit. Applied Nanotech developed, evaluated, and demonstrated indium inks/pates as high-density interconnects (HDI), in partnership with our subcontractors. We will design, model and manufacture printed superconducting interconnect ribbon cables for lowfrequency applications that will include shielding structures to mitigate external noise and internal (line-to-line) interference. The design will also include printed noise mitigation structures and components on both input and output to mitigate multiple noise sources. We will test these circuits in both normal and superconducting states. We will demonstrate the feasibility of shielded contacts and show the feasibility of making superconducting-on-normal copper or silver interconnects that allow superior signal carrying capabilities and noise mitigation in both superconducting and non-superconducting states, with the intent of making continuous, shielded, roll-to-roll, noise mitigation cable from mK to room temperature in one cable, eliminating the need for intermediate connectors. If successful, this will mitigate noise sources to the SuperCDMS sensor, increasing the sensitivity of the detector for finding dark energy. It will also lower costs and reduce thermal leakage to allow for lower temperatures and/or longer times between temperature cycling for longer periods of observation. This technology will also be critical to quantum computing applications where noise mitigation is important for reliability and stability.