Magnetic Gradient Fluctuations from Quadrupolar $^{73}$Ge in Si/SiGe Exchange-Only Qubits

TL;DR

This study investigates magnetic gradient noise in Si/SiGe quantum dots, revealing that quadrupolar precession of $^{73}$Ge nuclei significantly impacts spin coherence times, with implications for quantum computing qubit stability.

Contribution

It identifies the role of quadrupolar $^{73}$Ge nuclei in magnetic noise and characterizes their impact on qubit coherence in Si/SiGe quantum dots.

Findings

$^{73}$Ge quadrupolar precession influences $T_2$ decay times.

$^{73}$Ge noise peaks at Larmor resonance harmonics.

Material and magnetic field affect noise characteristics.

Abstract

We study the time-fluctuating magnetic gradient noise mechanisms in pairs of Si/SiGe quantum dots using exchange echo noise spectroscopy. We find through a combination of spectral inversion and correspondence to theoretical modeling that quadrupolar precession of the $^{73}$Ge nuclei play a key role in the spin-echo decay time $T_2$, with a characteristic dependence on magnetic field and the width of the Si quantum well. The $^{73}$Ge noise peaks appear at the fundamental and first harmonic of the $^{73}$Ge Larmor resonance, superimposed over $1/f$ noise due to $^{29}$Si dipole-dipole dynamics, and are dependent on material epitaxy and applied magnetic field. These results may inform the needs of dynamical decoupling when using Si/SiGe quantum dots as qubits in quantum information processing devices.