3D Integrated Embedded Filters for Superconducting Quantum Circuits

TL;DR

This paper introduces a novel multilayer PCB-integrated microwave Purcell filter for superconducting qubits, enhancing scalability, qubit isolation, and compatibility with high-coherence quantum devices.

Contribution

It presents a new off-chip filter design that simplifies device layout and enables multiplexed readout for large-scale superconducting quantum circuits.

Findings

Thousand-fold improvement in qubit isolation predicted by simulations

Experimental validation shows high coherence with median T1 of 84 μs

Compatible with 35-qubit superconducting quantum device

Abstract

Microwave filtering for superconducting qubits is a key element of quantum computing technology, enabling high coherence and fast state detection. This work presents the design and implementation of novel microwave Purcell filters for superconducting quantum circuits, integrated within a multilayer printed circuit board (PCB). The off-chip design removes all filter components from the qubit substrate, reducing device complexity, improving layout footprint and allowing better scalability to large qubit counts. Each embedded filter can couple up to nine readout resonators, enabling efficient multiplexed readout. Electromagnetic simulations of the filter predict a thousand-fold improvement in qubit isolation from the readout port. The design was experimentally validated under cryogenic conditions in conjunction with a 35-qubit device, demonstrating compatibility of the PCB-based filter with high-coherence superconducting qubits. The comparison of the measured qubit median T1 of 84 $\mu$s with the expected radiative limit from electromagnetic simulations validated the presence of Purcell filtering in the system.