Reducing strain in heterogeneous quantum devices using atomic layer deposition

TL;DR

This paper explores using atomic layer deposition dielectric layers to reduce strain in silicon/superconductor quantum devices at cryogenic temperatures, improving coherence without affecting $T_2$ times.

Contribution

It demonstrates that ALD layers can mitigate strain near interfaces and that biasing at the hyperfine clock transition removes strain broadening without impacting $T_2$.

Findings

ALD layers reduce strain near silicon/superconductor interfaces.

Biasing at the hyperfine clock transition removes strain broadening.

$T_2$ times remain unchanged with ALD layers in natural silicon devices.

Abstract

We investigated the use of dielectric layers produced by atomic layer deposition (ALD) as an approach to strain mitigation in composite silicon/superconductor devices operating at cryogenic temperatures. We show that the addition of an ALD layer acts to reduce the strain of spins closest to silicon/superconductor interface where strain is highest. We show that appropriately biasing our devices at the hyperfine clock transition of bismuth donors in silicon, we can remove strain broadening and that the addition of ALD layers left $T_2$ (or temporal inhomogeneities) unchanged in these natural silicon devices.