Magnetic Gradient Fluctuations from Quadrupolar <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><mml:msup><mml:mrow/><mml:mn>73</mml:mn></mml:msup><mml:mi>Ge</mml:mi></mml:math> in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><mml:mi>Si</mml:mi></mml:math>/<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><mml:mi>Si</mml:mi><mml:mi>Ge</mml:mi></mml:math> Exchange-Only Qubits
J. Kerckhoff, B. Sun, B.H. Fong, C. Jones, A.A. Kiselev, D.W. Barnes, R.S. Noah, E. Acuna, M. Akmal, S.D. Ha, J.A. Wright, B.J. Thomas, C.A.C. Jackson, L.F. Edge, K. Eng, R.S. Ross, T.D. Ladd
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.