Spin relaxation and coherence times for electrons at the Si/SiO₂ interface

While electron spins in silicon heterostructures make attractive qubits, little is known about the coherence of electrons at the Si/ SiO₂ interface. We report spin relaxation (T₁) and coherence (T ₂) times for mobile electrons and natural quantum dots at a S 28 i/ SiO₂ interface. Mobile electrons have short T₁ and T ₂ of 0.3 μs at 5 K. In line with predictions, confining electrons and cooling increases T₁ to 0.8 ms at 350 mK. In contrast, T ₂ for quantum dots is around 10 μs at 350 mK, increasing to 30 μs when the dot density is reduced by a factor of two. The quantum dot T ₂ is shorter than T₁, indicating that T₂ is not controlled by T₁ at 350 mK but is instead limited by an extrinsic mechanism. The evidence suggests that this extrinsic mechanism is an exchange interaction between electrons in neighboring dots.