Suspending superconducting qubits by silicon micromachining

TL;DR

This paper introduces a micromachining technique to suspend aluminum transmon qubits from silicon substrates, altering their noise environment and improving coherence times.

Contribution

The authors demonstrate a simple, high-yield method for suspending superconducting qubits, significantly changing their dielectric and flux noise characteristics.

Findings

Suspended qubits show longer T1 coherence times.

Suspension modifies dielectric participation ratios.

Flux noise increases in suspended qubits.

Abstract

We present a method for relieving aluminum 3D transmon qubits from a silicon substrate using micromachining. Our technique is a high yield, one-step deep reactive ion etch that requires no additional fabrication processes, and results in the suspension of the junction area and edges of the aluminum film. The drastic change in the device geometry affects both the dielectric and flux noise environment experienced by the qubit. In particular, the participation ratios of various dielectric interfaces are significantly modified, and suspended qubits exhibited longer $T_1$'s than non-suspended ones. We also find that suspension increases the flux noise experienced by tunable SQUID-based qubits.