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Acta Physica Polonica A

Electron Spin Dephasing in a Double Quantum Dot Canceled via a Magnetic-Field Gradient

Michał Gawełczyk

Published Oct 1, 2018• 1 citation
Publisher

Abstract

Phonon-assisted tunneling of electrons between nonidentical quantum dots in a magnetic field has been recently shown to be affected by a spin pure dephasing.The process is due to the mismatch of the Zeeman splittings caused by the difference of effective electron g-factors in the two dots.Based on both analytical estimation and an accurate numerical modeling of a double quantum dot system, we show that this dephasing can be canceled by applying an appropriately tuned magnetic-field gradient that compensates for the built-in inequality of the Zeeman splittings.

DOI
10.12693/aphyspola.134.926

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Phonon-assisted tunneling of electrons between nonidentical quantum dots in a magnetic field has been recently shown to be affected by a spin pure dephasing.The process is due to the mismatch of the Zeeman splittings caused by the difference of effective electron g-factors in the two dots.Based on both analytical estimation and an accurate numerical modeling of a double quantum dot system, we show that this dephasing can be canceled by applying an appropriately tuned magnetic-field gradient that compensates for the built-in inequality of the Zeeman splittings.
We predict a spin pure dephasing channel in electron relaxation between states with unequal Zeeman splittings, exemplified by a spin-preserving electron tunneling between quantum dots in a magnetic field. The dephasing is caused by a mismatch in electron ggg factors in the dots leading to distinguishability of phonons emitted during tunneling with opposite spins. Combining multiband $\mathbit{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbit{p}$ modeling and dynamical simulations via a master equation, we show that this fundamental effect of spin measurement effected by the phonon bath may be widely controlled by the size and composition of the dots or on demand via tuning of external fields. By comparing the numerically simulated degree of dephasing with the predictions of general theory based on distinguishability of environment states, we show that the proposed mechanism is the dominant phonon-related spin dephasing channel and may limit spin coherence time in tunnel-coupled structures at cryogenic temperatures.
In this contribution we study carrier tunneling in a system consisting of a pair of coupled quantum dots.We predict the presence of a spin dephasing channel in such a system, which is associated with a "welcher-weg" type of decoherence process occurring during carrier tunneling.In our model such a process is caused by a mismatch of g-factor values in two quantum dots in the presence of external magnetic field.This leads to a mismatch in spin Zeeman splitting between the dots and, in consequence, to the distinguishability of phonons emitted during the tunneling of carriers with opposite spins.Thus we demonstrate a process of spin dephasing without any direct spin-environment coupling present in the model.
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We have theoretically studied phonon-mediated spin-flip processes of electrons in a GaAs double quantum dot (DQD) holding two spins, under a phonon temperature gradient over the DQD. Transition rates of interdot phonon-assisted tunnel processes and intradot spin-flip processes involving spin triplet states are formalized by the electron-phonon interaction accompanied with the spin-orbit interaction. The calculations of the spin-flip rates and the occupation probabilities of the spin-states in the two-electron DQD with respect to the phonon temperature difference between the dots are quantitatively consistent with our previous experiment. This theoretical study on the temperature gradient effect onto spins in coupled QDs would be essential for understanding spin-related thermodynamic physics.