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arXiv:1511.08434 · Scientific Reports

Phonon-mediated generation of quantum correlations between quantum dot qubits

Jan A. Krzywda, Katarzyna Roszak

Published Apr 1, 2016• 21 citations
arXivHTMLPDF

Abstract

We study the generation of quantum correlations between two excitonic quantum dot qubits due to their interaction with the same phonon environment. Such generation results from the fact that during the pure dephasing process at finite temperatures, each exciton becomes entangled with the phonon environment. We find that for a wide range of temperatures quantum correlations are created due to the interaction. The temperature-dependence of the level of correlations created displays a trade-off type behaviour; for small temperatures the phonon-induced distrubance of the qubit states is too small to lead to a distinct change of the two-qubit state, hence, the level of created correlations is small, while for large temperatures the pure dephasing is not accompanied by the creation of entanglement between the qubits and the environment, so the environment cannot mediate qubit-qubit quantum correlations.

DOI
10.1038/srep23753

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Self-assembled quantum dots (QDs) are ideal structures in which to test theories of open quantum systems: confined exciton states can be coherently manipulated and their decoherence properties are dominated by interactions with acoustic phonons. We here describe the interaction of a pair of un-coupled, driven, QD excitons with a common phonon environment, and find that this coupling effectively generates two kinds of interaction between the two QDs: an elastic coupling mediated by virtual phonons and an inelastic coupling mediated by real phonons. We show that both of these interactions produce steady state entanglement between the two QD excitons. We also show that photon correlations in the emission of the QDs can provide a signature of the common environment. Experiments to demonstrate our predictions are feasible with the state-of-the-art technology and would provide valuable insight into QD carrier–phonon dynamics.
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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.
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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.