# Superconducting qubits on silicon substrates for quantum device integration

## TL;DR

This paper demonstrates the fabrication and characterization of superconducting transmon qubits on silicon substrates, achieving coherence times comparable to sapphire, and enabling potential integration with silicon photonics for quantum networking.

## Contribution

It introduces a novel fabrication process for superconducting qubits on silicon substrates, including SOI, facilitating integration with silicon photonic and mechanical components.

## Key findings

- Qubit lifetimes up to 27 microseconds on silicon substrates.
- Coherence times comparable to sapphire-based qubits.
- Process enables integration with silicon photonics for quantum devices.

## Abstract

We present the fabrication and characterization of transmon qubits formed from aluminum Josephson junctions on two different silicon-based substrates: (i) high-resistivity silicon (Si) and (ii) silicon-on-insulator (SOI). Key to the qubit fabrication process is the use of an anhydrous hydrofluoric vapor process which removes silicon surface oxides without attacking aluminum, and in the case of SOI substrates, selectively removes the lossy buried oxide underneath the qubit region. For qubits with a transition frequency of approximately $5$GHz we find qubit lifetimes and coherence times comparable to those attainable on sapphire substrates ($T_{1,\text{Si}} = 27\mu$s, $T_{2,\text{Si}} = 6.6\mu$s; $T_{1,\text{SOI}} = 3.5\mu$s, $T_{2,\text{SOI}} = 2.2\mu$s). This qubit fabrication process in principle permits co-fabrication of silicon photonic and mechanical elements, providing a route towards chip-scale integration of electro-opto-mechanical transducers for quantum networking of superconducting microwave quantum circuits.