Spin relaxation of a donor electron coupled to interface states

TL;DR

This paper investigates phonon-assisted spin relaxation in silicon donor electron qubits coupled to interface states, revealing magnetic field-dependent behaviors, hot-spots, and cool-spots that impact quantum information processing.

Contribution

It provides a detailed analysis of spin relaxation mechanisms involving hybridized states and identifies conditions for optimizing qubit coherence and initialization.

Findings

Spin relaxation exhibits a B^5 dependence at weak magnetic fields.

Identification of spin relaxation hot-spots and cool-spots due to state hybridization.

Implications for fast spin initialization and quantum information preservation.

Abstract

An electron spin qubit in a silicon donor atom is a promising candidate for quantum information processing because of its long coherence time. To be sensed with a single-electron transistor, the donor atom is usually located near an interface, where the donor states can be coupled with interface states. Here we study the phonon-assisted spin-relaxation mechanisms when a donor is coupled to confined (quantum-dot-like) interface states. We find that both Zeeman interaction and spin-orbit interaction can hybridize spin and orbital states, each contributing to phonon-assisted spin relaxation in addition to the spin relaxation for a bulk donor or a quantum dot. When the applied magnetic field $B$ is weak (compared to orbital spacing), the phonon assisted spin relaxation shows the $B^5$ dependence. We find that there are peaks (hot-spots) in the $B$-dependent and detuning dependent spin relaxation due to strong hybridization of orbital states with opposite spin. We also find spin relaxation dips (cool-spots) due to the interference of different relaxation channels. Qubit operations near spin relaxation hot-spots can be useful for the fast spin initialization and near cool-spots for the preservation of quantum information during the transfer of spin qubits.