Scaled Production of High-Density Cryogenic Flexible coAXial (FLAX) RF Ribbon Cables

Cryogenic wiring is a critical component for quantum computers, superconducting supercomputers, transition-edge sensors, microwave kinetic inductance detectors, and a wide range of other applications. Quantum computing has risen to prominence as a key use for cryogenic wiring, given its profound national security implications and potential for fundamental transformation of industries ranging from logistics and agriculture to medicine and climate change. The quantum future will require a new supply chain to help lift quantum technologies out of laboratories and into scaled commercial use. US leadership in this supply chain is critical to maintaining our place as a global technology leader. While some quantum technologies are obviously complex, such as sub-Kelvin cryogenic systems or qubits, even seemingly straightforward elements of a quantum system, such as wiring, are subject to rigorous technical requirements and a global supply pinch. The wires used in superconducting systems are typically a major factor in total system cost and an obstacle to scaling up system performance. Today, RF wires are commercially sourced from just a few international suppliers such as CoaxCo (Japan), CryoCoax/Intelliconnect (UK), Delft Circuits (Netherlands), or a handful of Chinese companies. Semi-rigid superconducting coax cables have been relied on as the backbone of low-temperature quantum systems for decades, with benefits including reliability, a large number of compatible components, and good RF qualities. However, semi-rigid coax cables have a large physical footprint, large thermal load, and high stiffness, limiting how many wires can fit in a cryogenic system. Deposited metal-on-insulator cables have recently started being manufactured as an alternative. However, these cables still suffer from serious limitations. Their fabrication relies on metal deposition in vacuum which limits wire length, increases manufacturing costs, and dramatically slows production speed. Finally, both semi-rigid coax and metal-on-insulator cables have lower than optimal density, leading to practical limits on the number of qubits that can be installed in commercially available cryogenic systems. They are also exorbitantly expensive -- any individual wire can easily cost $1,000-5,000, depending on technology, meaning that wiring a gate-based quantum computer can cost more than $1M. Moreover, lead times on delivery of these wires are typically at least several months. The novel flexible coaxial cables to be produced as a result of this proposal creates a new type of high-density data cable for superconducting electronics applications which have high density, low attenuation, low crosstalk, low stiffness, low heat load, and can be manufactured efficiently at scale and any length. It builds on the outstanding performance achieved by Maybell and UCSB with small-scale production and leverages established manufacturing technology to scale and economize production.