Nuclear Dynamics in Isotopically Enhanced Silicon Spin Qubits

Nuclear dipole-dipole dynamics have long been identified as a problem for silicon qubits. Early NMR and spin-qubit experiments in dense nuclear lattices such as GaAs characterized nuclear dynamics as classical spin diffusion, amounting to “Brownian motion” of the nuclear magnetization as seen by an electron spin. However, recent experiments in Si/SiGe qubits, phosphorus impurity qubits, and MOS qubits in both isotopically natural and isotopically purified samples point to more complex behavior, showing a noise spectrum with a 1/f spectrum at low frequency and some indications of measurement back-action. This talk will survey these various results and provide rough models for these observations, and will include a discussion of the challenges for efforts to model complex dipole-dipole behavior using more quantitative many-body spin models.