Integration of Through‐Sapphire Substrate Machining with Superconducting Quantum Processors

Abstract A sapphire machining process integrated with intermediate‐scale quantum processors is demonstrated. The process allows through‐substrate electrical connections, necessary for low‐frequency mode‐mitigation, as well as signal‐routing, which are vital as quantum computers scale in qubit number, and thus dimension. High‐coherence qubits are required to build fault‐tolerant quantum computers and so material choices are an important consideration when developing a qubit technology platform. Sapphire, as a low‐loss dielectric substrate, has shown to support high‐coherence qubits. In addition, recent advances in material choices such as tantalum and titanium‐nitride, both deposited on a sapphire substrate, have demonstrated qubit lifetimes exceeding 0.3 ms. However, the lack of any process equivalent of deep‐silicon etching to create through‐substrate‐vias in sapphire, or to inductively shunt large dies, has limited sapphire to small‐scale processors, or necessitates the use of chiplet architecture. Here, a sapphire machining process that is compatible with high‐coherence qubits is presented. This technique immediately provides a means to scale quantum processing units (QPUs) with integrated mode‐mitigation, and provides a route toward the development of through‐sapphire‐vias, both of which allow the advantages of sapphire to be leveraged as well as facilitating the use of sapphire‐compatible materials for large‐scale QPUs.