High coherence in a tileable superconducting circuit

We demonstrate state-of-the-art qubit coherence and single-qubit gate fidelities in a readily extensible superconducting circuit architecture. Our 4-qubit device features 3D integrated off-chip control wiring, readout-resonators fabricated on the reverse-side of the circuit substrate, and an inductively shunted enclosure. We establish these technologies are compatible with high qubit coherence, measuring average T₁ = 148 µs. We provide a careful experimental analysis of packaging crosstalk and show that the off-chip wiring is highly selective. The coherence and crosstalk results are borne out in simultaneous randomized benchmarking, where we measure average single-qubit gate fidelities >99.98%. By considering band-structure, we show the device contains a unit-cell that can tile the plane while still providing a clean electromagnetic environment for qubits; with spatially exponentially decaying packaging crosstalk between qubits. Our results demonstrate a promising 3D integrated architecture for creating large 2D arrays of superconducting qubits, using current superconducting qubit fabrication techniques.