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arXiv:cond-mat/0702428

Phonon-assisted decoherence in coupled quantum dots

Alagu Thilagam, Max A. Lohe

Published Feb 19, 2007• 1 citation
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Abstract

We analyse various phonon-assisted mechanisms which contribute to the decoherence of excitonic qubits in quantum dot systems coupled by the Förster-type transfer process. We show the significant loss of coherence accompanied by dissipation due to charge carrier oscillations between qubit states by using a model of one-phonon assisted Förster-type transfer process. We obtain explicit expressions for the relaxation and dephasing times for excitonic qubits interacting with acoustic phonons via both deformation potential and piezoelectric coupling. We compare the decoherence times of the GaAs/AlGaAs material system with half times of concurrence decay in a 2$\otimes$2 bipartite mixed excitonic qubit system. We extend calculations to determine the influence of phonon mediated interactions on the non-unitary evolution of Berry phase in quantum dot systems.

DOI
10.48550/arxiv.cond-mat/0702428

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We analyse various phonon-assisted mechanisms which contribute to the decoherence of excitonic qubits in quantum dot systems coupled by the Förster-type transfer process. We show the significant loss of coherence accompanied by dissipation due to charge carrier oscillations between qubit states by using a model of one-phonon assisted Förster-type transfer process. We obtain explicit expressions for the relaxation and dephasing times for excitonic qubits interacting with acoustic phonons via both deformation potential and piezoelectric coupling. We compare the decoherence times of the GaAs/AlGaAs material system with half times of concurrence decay in a 2⊗\otimes⊗2 bipartite mixed excitonic qubit system. We extend calculations to determine the influence of phonon mediated interactions on the non-unitary evolution of Berry phase in quantum dot systems.
We investigate phonon-assisted mechanisms which contribute to the decoherence of excitonic qubits in quantum dot systems coupled by a Förster-type transfer process. Using the Fermi Golden Rule, we derive explicit expressions for the relaxation and dephasing times for excitonic qubits interacting with acoustic phonons via both the deformation potential and piezoelectric coupling. The decoherence times computed using the Fermi Golden Rule are consistent with those estimated using Bloch–Redfield theory at interdot tunnelling energies small enough for Markovian theories to be valid. Our results show that renormalization of interdot tunnelling frequencies due to phonon interactions is influenced mainly by bias and lattice temperature in GaAs/AlGaAs quantum dot systems.
We investigate the influence of phonon mediated interactions on the non-unitary evolution of geometrical phases in excitonic qubits formed in quantum dots entangled by pure Förster coupling. We consider decoherence to occur via acoustic phonons interacting through the deformation potential and piezoelectric coupling mechanisms. The influences of bath temperature, external electric field, quantum dot size and interdot distance on the evolution of geometrical phases are examined for the GaAs/AlGaAs material system. We extend the theory to determine the effect of dynamic decoupling employing ultrafast π-pulses on the evolution of geometrical phases in the presence of dephasing processes.
In this paper we investigate decoherence times of a double quantum dot (DQD) charge qubit due to it coupling with acoustic phonon baths. We individually consider the acoustic piezoelectric as well as deformation coupling phonon baths in the qubit environment. The decoherence times are calculated with two kinds of methods. One of them is based on the qusiadiabatic propagator path integral (QUAPI) and the other is based on Bloch equations, and two kinds of results are compared. It is shown that the theoretical decoherence times of the DQD charge qubit are shorter than the experimental reported results. It implies that the phonon couplings to the qubit play a subordinate role, resulting in the decoherence of the qubit.
This chapter is devoted to the recent theoretical results on the optical quantum control over charges confined in quantum dots under influence of phonons. We show that lattice relaxation processes lead to decoherence of the confined carrier states. The theoretical approach leading to a uniform, compact description of the phonon impact on carrier dynamics, perturbative in phonon couplings but applicable to arbitrary unperturbed evolution, is described in detail. Next, some applications are presented: phonon damping of Rabi oscillations in quantum dots and phonon-induced error of a single-qubit gate for an excitonic quantum dot qubit as well as for a semiconductor quantum dot spin qubit operated via a STIRAP transfer.