3D-integrated filters for superconducting quantum circuits

A key challenge for superconducting qubit architectures is designing a scalable system that enables fast state readout while maintaining high coherence. Purcell filtering has become a widespread tool used to protect qubits from unwanted radiative relaxation through such readout channels. These extra filter circuit elements, often realised by transmission-line or lumped-element layouts, increase the physical footprint of each superconducting qubit. This has led to multi-chip designs typically requiring wire-bonding or superconducting bump-bonding increasing packaging complexity. Here we present an alternative 3D-integrated superconducting qubit package with Purcell filters. This design enables readout multiplexing, does not increase the physical footprint of the device, and has compatibility for arrays of thousands of qubits. We demonstrate this packaging with a thirty-qubit device and show coherence times above one hundred microseconds. Analysis of filter protection and bandwidth will also be presented.