Acta Physica Polonica A

Phonon-Induced Pure Dephasing of Two-Electron Spin States in Vertical Quantum Dot Molecules

Katarzyna Roszak, Paweł Machnikowski

Published Nov 1, 2009• 1 citation

Abstract

Phonon-induced dephasing of two-electron spin states in two vertically stacked self-assembled GaAs/InGaAs quantum dots is studied.A pure dephasing process due to elastic phonon scattering is found to dominate at low temperatures.This process is independent of the spin-orbit coupling and does not require the presence of a magnetic field.It relies on interdot tunneling and the Pauli principle, which make the double quantum dot gate for spin based quantum computing possible, and therefore cannot be avoided.

DOI: 10.12693/aphyspola.116.877

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Acta Physica Polonica A

Phonon-Induced Pure Dephasing of Two-Electron Spin States in Vertical Quantum Dot Molecules

Katarzyna Roszak, Paweł Machnikowski

Published Nov 1, 2009• 1 citation

Publisher

Abstract

DOI: 10.12693/aphyspola.116.877

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arXiv:1707.06155Physical review. B./Physical review. BAug 3, 201811 citations

We study theoretically the phonon-induced relaxation (

{T}_{1}

) and decoherence times (

{T}_{2}

) of singlet-triplet qubits in lateral GaAs double quantum dots (DQDs). When the DQD is biased, Pauli exclusion enables strong dephasing via two-phonon processes. This mechanism requires neither hyperfine nor spin-orbit interaction and yields ${T}_{2}\ensuremath{\ll}{T}_{1}$, in contrast to previous calculations of phonon-limited lifetimes. When the DQD is unbiased, we find ${T}_{2}\ensuremath{\simeq}2{T}_{1}$ and much longer lifetimes than in the biased DQD. For typical setups, the decoherence and relaxation rates due to one-phonon processes are proportional to the temperature

T

, whereas the rates due to two-phonon processes reveal a transition from

{T}^{2}

to higher powers as

T

is decreased. Remarkably, both

{T}_{1}

and

{T}_{2}

exhibit a maximum when the external magnetic field is applied along a certain axis within the plane of the two-dimensional electron gas. We compare our results with recent experiments and analyze the dependence of

{T}_{1}

and

{T}_{2}

on system properties such as the detuning, the spin-orbit parameters, the hyperfine coupling, and the orientation of the DQD and the applied magnetic field with respect to the main crystallographic axes.

g

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.