SiGe/Si quantum dot electron spin decoherence dependence on $^{73}$Ge

TL;DR

This paper theoretically investigates how the presence of $^{73}$Ge nuclear spins in SiGe barriers affects electron spin decoherence times in silicon quantum dots, emphasizing the importance of isotope enrichment for quantum coherence.

Contribution

It provides atomistic tight-binding calculations of decoherence times considering $^{73}$Ge, highlighting the impact of Ge isotopic composition on quantum dot coherence.

Findings

Decoherence times due to natural Ge isotopic abundance are in the milliseconds range.

Enrichment of Ge isotopes is necessary for achieving longer coherence times in SiGe/Si quantum dots.

Comparison of $T_2$ times across different isotope fractions informs material optimization for quantum devices.

Abstract

We theoretically study the nuclear spin induced decoherence of a quantum dot in Si that is confined at a SiGe interface. We calculate decoherence time dependence on $^{73}$Ge in the barrier layer to evaluate the importance of Ge as well as Si enrichment for long decoherence times. We use atomistic tight-binding modeling for an accurate account of the electron wavefunction which is particularly important for determining the contact hyperfine interactions with the Ge nuclear spins. We find decoherence times due to Ge spins at natural concentrations to be milliseconds. This suggests SiGe/Si quantum dot devices employing enriched Si will require enriched Ge as well in order to benefit from long coherence times. We provide a comparison of $T_2$ times for various fractions of nonzero spin isotopes of Si and Ge.