New Source of Spin-hot spot in displaced silicon double quantum dots

TL;DR

This study reveals a new type of spin-hot spot in displaced silicon double quantum dots, characterized by ultra-low spin-relaxation rates at low magnetic fields, promising for quantum computing applications.

Contribution

It identifies a novel spin-hot spot in displaced silicon double quantum dots with significantly reduced relaxation rates, advancing understanding of spin dynamics in quantum dot systems.

Findings

In double quantum dots, a new spin-hot spot appears as dots are pulled apart.

Spin-relaxation rates at these hot spots can be three orders of magnitude lower than in single dots.

Oscillations in spin-hot spots occur at low magnetic fields (~1T), with relaxation times from milliseconds to picoseconds.

Abstract

Controlling electron spins in double quantum dots allows individual electrons to be trapped and manipulated for next-generation solid-state qubit devices. In this paper, the study analyzes spin relaxation due to deformation potentials of acoustic phonon in single and double quantum dots under in-plane and out-of-plane magnetic fields, showing that in single quantum dots the relaxation rate is highly sensitive to low in-plane magnetic fields ($<1T$) but converges near a spin-hot-spot region. In a single quantum dot, the spin-hot spot arises from well-understood level crossings between singlet and triplet states. In double quantum dots, a new and unusual spin-hot spot appears as the dots are pulled apart from the origin, with spin-relaxation rates three orders of magnitude lower than conventional single quantum dots. In displaced quantum dots dominated by magnetic confinement, two distinct spin-hot spots appear at different in-plane magnetic field strengths, where spin-relaxation time varies from millisecond to picosecond. When quantum dots are separated by about 60 nm, calculations predict oscillations in spin-hot spots as the in-plane magnetic field changes. These unusual spin-hot spot oscillations occur at low magnetic fields ($<1T$), resulting in spin-relaxation rates about four orders of magnitude lower than those of conventional high-field spin-hot spots ($\approx 4.5T$). The extremely low spin-relaxation rate at the spin-hot spot enables the preparation of qubit superposition states for quantum computing and information processing.