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

TL;DR

This study measures spin relaxation and coherence times for electrons at the Si/SiO2 interface, revealing how confinement and temperature influence these quantum properties and identifying extrinsic mechanisms limiting coherence.

Contribution

It provides the first detailed measurements of T1 and T2 for electrons at the Si/SiO2 interface, highlighting the impact of quantum dot density and temperature on spin coherence.

Findings

Mobile electrons have T1 and T2 of 0.3 μs at 5 K.

Confinement and cooling increase T1 to 0.8 ms at 350 mK.

Quantum dot T2 is around 10 μs at 350 mK, increasing with lower dot density.

Abstract

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 (T2) times for mobile electrons and natural quantum dots at a 28Si/SiO2 interface. Mobile electrons have short T1 and T2 of 0.3 us at 5 K. In line with predictions, confining electrons and cooling increases T1 to 0.8 ms at 350 mK. In contrast, T2 for quantum dots is around 10 us at 350 mK, increasing to 30 us when the dot density is reduced by a factor of two. The quantum dot T2 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.