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

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 the 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 the 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.