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Heliyon

The impact of phonon-assisted tunneling on optical and quantum characteristics of a coupled two-quantum dot system

Santiago Echeverri-Arteaga, Herbert Vinck-Posada, Edgar A. Gómez

Published Jul 24, 2023• 4 citations
Publisher

Abstract

This work investigates the impact of decoherence induced by pure dephasing and phonon-assisted tunneling mechanisms on the optical and quantum properties of two quantum dots. Special attention is given to the density matrix at steady state, and a detailed analysis of populations, coherences, optical transitions and the emission spectrum is performed. Additionally, we study the influence of both phonon-decoherence mechanisms on bipartite entanglement and the degree of mixedness of the system. In particular, our findings indicate that the phonon-assisted tunneling mechanism partially affects the coherences of the system and quantum properties when the imbalance of phonon absorption and emission is significant. Conversely, the pure dephasing mechanism does not affect the populations but strongly entangles the quantum dots and the reservoir, inducing maximally mixed states and significantly reducing the spectral splitting in the emission spectrum of the system.

DOI
10.1016/j.heliyon.2023.e18451

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This work investigates the impact of decoherence induced by pure dephasing and phonon-assisted tunneling mechanisms on the optical and quantum properties of two quantum dots. Special attention is given to the density matrix at steady state, and a detailed analysis of populations, coherences, optical transitions and the emission spectrum is performed. Additionally, we study the influence of both phonon-decoherence mechanisms on bipartite entanglement and the degree of mixedness of the system. In particular, our findings indicate that the phonon-assisted tunneling mechanism partially affects the coherences of the system and quantum properties when the imbalance of phonon absorption and emission is significant. Conversely, the pure dephasing mechanism does not affect the populations but strongly entangles the quantum dots and the reservoir, inducing maximally mixed states and significantly reducing the spectral splitting in the emission spectrum of the system.
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 the dynamical behavior of entanglement in a system made of two solid-state emitters, as two quantum dots, embedded in two separated microcavities. In these solid-state systems, in addition to the coupling with the cavity mode, the emitter is coupled to a continuum of leaky modes providing additional losses and is also subjected to a phonon-induced pure dephasing mechanism. We model this physical configuration as a multipartite system composed of two independent parts each containing a qubit embedded in a single-mode cavity, exposed to cavity losses, spontaneous emission and pure dephasing. We study the time evolution of entanglement of this multipartite open system, finally applying this theoretical framework to the case of currently available solid-state quantum dots in microcavities.
We investigate a quantum dot (QD) system coupled to a vibrational environment with a super-Ohmic spectral density and weakly to a leaky cavity mode, a model relevant for semiconductor-based single-photon sources. The phonon coupling induces dephasing and broadens the absorption and emission line shapes, while the weakly coupled cavity mode leads to effective driving of the QD. To capture non-Markovian effects, we use non-Markovian Quantum State Diffusion and its hierarchical extension the Hierarchy of Pure States to compute multitime correlation functions underlying absorption and resonance fluorescence spectra. We present numerical results for the absorption spectra at strong phonon coupling and finite temperature, as well as for resonance fluorescence spectra at varying phonon coupling strengths and temperatures, and analyse the visibility of the resonance fluorescence spectra to provide insights into how phonon coupling and thermal effects influence the spectral features.
We present a theoretical study of vacuum-induced coherence in a pair of vertically stacked semiconductor quantum dots. The process consists in a coherent excitation transfer from a single-exciton state localized in one dot to a delocalized state in which the exciton occupation gets trapped. We study the influence of the factors characteristic of quantum dot systems (as opposed to natural atoms): energy mismatch, coupling between the single-exciton states localized in different dots, and different and nonparallel dipoles due to sub-band mixing, as well as coupling to phonons. We show that the destructive effect of the energy mismatch can be overcome by an appropriate interplay of the dipole moments and coupling between the dots which allows one to observe the trapping effect even in a structure with technologically realistic energy splitting of the order of milli--electron volts. We also analyze the impact of phonon dynamics on the occupation trapping and show that phonon effects are suppressed in a certain range of system parameters. This analysis shows that the vacuum-induced coherence effect and the associated long-living trapped excitonic population can be achieved in quantum dots.
Realizing scalable quantum networks requires a meticulous level of understanding and mitigating the deleterious effects of decoherence. Many quantum device platforms feature multiple decoherence mechanisms, often with a dominant mechanism seemingly fully masking others. In this paper, we show how access to weaker dephasing mechanisms can nevertheless be obtained for optically active qubits by performing two-photon coincidence measurements. To this end we theoretically investigate the impact of different decoherence mechanisms on cooperatively emitting quantum dots. Focusing on the typically dominant deformation-potential coupling to longitudinal acoustic phonons and typically much less severe additional sources of pure dephasing, we employ a numerically exact method to show that these mechanisms lead to very different two-photon coincidence signals. Moreover, surprisingly, the impact of the strongly coupled phonon environment is weak and leads to long-lived coherences. We trace this back to the superohmic nature of the deformation-potential coupling causing interemitter coherences to converge to a nonzero value on a short timescale, whereas pure dephasing contributions cause a complete decay of coherence over longer times. Our approach provides a practical means of investigating decoherence processes on different timescales in solid-state emitters, and thus contributes to understanding and possibly eliminating their detrimental influences.