3D integration of superconducting quantum systems – part 3: Preserving qubit coherence*

We demonstrate the operation and local control of high-coherence capacitively-shunted flux qubits (CSFQs) in a 3D-integrated 3-tier architecture. Qubits are fabricated both on the qubit and interposer tiers using high-coherence processes. Readout and control components, including resonators and flux bias lines, are located on the interposer tier, and are accessed through superconducting through-silicon vias (TSVs) and bump bonds from a bottom-tier multi-layer superconducting multichip module (SMCM). Coherence of the CSFQs in the 3D-integrated stack is consistent with values typical for the single-tier processes – including with the dielectric-containing multilayer SMCM tier electrically coupled through the three-tier stack.