Singlet-triplet relaxation in SiGe/Si/SiGe double quantum dots

TL;DR

This paper investigates how singlet-triplet relaxation in SiGe/Si/SiGe double quantum dots is influenced by spin-orbit coupling, electron-phonon interactions, and external fields, revealing tunable transition rates and electric field insensitivity.

Contribution

It provides a detailed analysis of relaxation mechanisms considering Coulomb interaction and valley splitting, using exact diagonalization and Fermi golden rule, highlighting the tunability of transition rates.

Findings

Transition rates can be tuned by magnetic field and interdot distance.

Transition rates are nearly unaffected by electric field changes.

Relaxation behavior shows interesting features near anticrossing points.

Abstract

We study the singlet-triplet relaxation due to the spin-orbit coupling assisted by the electron-phonon scattering in two-electron SiGe/Si/SiGe double quantum dots in the presence of an external magnetic field in either Faraday or Voigt configuration. By explicitly including the electron-electron Coulomb interaction and the valley splitting induced by the interface scattering, we employ the exact-diagonalization method to obtain the energy spectra and the eigenstates. Then we calculate the relaxation rates with the Fermi golden rule. We find that the transition rates can be effectively tuned by varying the external magnetic field and the interdot distance. Especially in the vicinity of the anticrossing point, the transition rates show intriguing features. We also investigate the electric-field dependence of the transition rates, and find that the transition rates are almost independent of the electric field. This is of great importance in the spin manipulation since the lifetime remains almost the same during the change of the qubit configuration from $(1,1)$ to $(2,0)$ by the electric field.