Two-electron dephasing in single Si and GaAs quantum dots

TL;DR

This paper analyzes two-electron dephasing mechanisms in single Si and GaAs quantum dots, focusing on electron-phonon interactions and charge noise, revealing material-specific dephasing rates and the effects of anharmonicity and disorder.

Contribution

It provides a detailed analytical comparison of dephasing in GaAs and Si quantum dots, including effects of phonons, charge noise, anharmonicity, and disorder, highlighting material-specific differences.

Findings

GaAs dephasing rate ~5.9 GHz due to optical phonons

Si orbital dephasing rate ~140 kHz, valley excitations ~1.1 MHz

Charge noise is suppressed in ideal harmonic quantum dots

Abstract

We study the dephasing of two-electron states in a single quantum dot in both GaAs and Si. We investigate dephasing induced by electron-phonon coupling and by charge noise analytically for pure orbital excitations in GaAs and Si, as well as for pure valley excitations in Si. In GaAs, polar optical phonons give rise to the most important contribution, leading to a typical dephasing rate of ~5.9 GHz. For Si, intervalley optical phonons lead to a typical dephasing rate of ~140 kHz for orbital excitations and ~1.1 MHz for valley excitations. For harmonic, disorder-free quantum dots, charge noise is highly suppressed for both orbital and valley excitations, since neither has an appreciable dipole moment to couple to electric field variations from charge fluctuators. However, both anharmonicity and disorder break the symmetry of the system, which can lead to increased dipole moments and therefore faster dephasing rates.