Magnetic Gradient Fluctuations from Quadrupolar 73Ge 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 73Ge nuclei play a key role in the spin-echo decay time T2, with a characteristic dependence on the magnetic field and the width of the Si quantum well. The 73Ge noise peaks appear at the fundamental and first harmonic of the 73Ge Larmor resonance, superimposed over 1/f noise due to 29Si 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.