Spin incoherence of donor electrons near c-Si(111)/SiO2 interface defects

Electron and nuclear spins of phosphorous ($^{31}$P) donors in crystalline silicon have been investigated extensively in recent years as they both have extremely long quantum mechanical coherence times which makes them extremely interesting candidates for quantum information and spin-electronics applications [1]. Existing silicon quantum computer concepts [2] propose to use $^{31}$P qubits close to the silicon surface. We present here a study of how microscopic defects at the oxide layer of the silicon surface influence the spin coherence times (T$_{1}$ and T$_{2}$ times) of the $^{31}$P qubits. Using pulsed electrically detected magnetic resonance spectroscopy [3], we show that due to the interaction of the $^{31}$P qubits with the interface states, the previously known, extremely long bulk coherence times are drastically shortened [4]. \\[4pt] [1] J. J. L.Morton, et al., Nature \textbf{455}, 1085 (2008). \\[0pt] [2] B. E. Kane, Nature 393, 133 (1998). \\[0pt] [3] A. R. Stegner, et al., \textit{Nature Physics} 2, 835 (2006). \\[0pt] [4] S.-Y. Paik, et al., arXiv:cond-mat/0905.0416 (2009).