# Double-sided coaxial circuit QED with out-of-plane wiring

## TL;DR

This paper introduces a coaxial circuit QED architecture with out-of-plane wiring, enabling scalable, multi-qubit control and readout while maintaining coherence, demonstrated through experimental device characterization.

## Contribution

It presents a novel coaxial circuit QED design with out-of-plane wiring, facilitating scalable quantum computing architectures without compromising qubit coherence.

## Key findings

- Device characterized with T1 = 4.1 μs and T2 = 5.7 μs.
- Good agreement between measurements and simulations.
- Architecture supports large qubit arrays with out-of-plane wiring.

## Abstract

Superconducting circuits are well established as a strong candidate platform for the development of quantum computing. In order to advance to a practically useful level, architectures are needed which combine arrays of many qubits with selective qubit control and readout, without compromising on coherence. Here we present a coaxial circuit QED architecture in which qubit and resonator are fabricated on opposing sides of a single chip, and control and readout wiring are provided by coaxial wiring running perpendicular to the chip plane. We present characterisation measurements of a fabricated device in good agreement with simulated parameters and demonstrating energy relaxation and dephasing times of $T_1 = 4.1\,\mu$s and $T_2 = 5.7\,\mu$s respectively. The architecture allows for scaling to large arrays of selectively controlled and measured qubits with the advantage of all wiring being out of the plane.