Hybrid Bulk/Thin-Film 3D Resonators for Superconducting Quantum Circuits*

One of the leading candidate platforms for quantum computing is superconducting circuits. The resonant modes of superconducting microwave resonators offer a long-lived and hardware-efficient way to store quantum information, and offer significant advantages for quantum error correction. To optimize coherence, it is desirable to find ways of combining the long lifetimes and low surface participations of 3D cavities with the control of materials properties and mass producibility of conventional circuits. In this talk, I will present a way to improve the scalability of bosonic modes without sacrificing their coherence times. Our design combines a high-quality on-chip film with a simpler but high coherence package, and effectively eliminates the effects of the substrate bulk and surface losses. We combine this design with a transmon ancilla and show that it enables millisecond coherence times, on par with 3D cavities.