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Results in Optics

Refractive index change in a double quantum dot structure

Suha Hadi, Mohammed A. Abbas, Faten K. Hachim, Baqer Obaid Al-Nashy, Amin Habbeb AL-Khursan

Published Aug 5, 2025• 2 citations
Publisher

Abstract

The density matrix theory models the refractive index change in a double quantum dot (DQD) system. The orthogonalized plane wave (OPW) is considered for wetting layer (WL)-quantum dot (QD) transitions, and the transition momenta are calculated. The modeling here considers all possible QD-QD and WL-QD transitions, which is another key property of this work. The results show that the tunneling increment raises the refractive change (RIC) to a huge value. Reducing the probe field enables the superluminal propagation of light, which is of viable importance in optical applications. A weaker probe or a strong pump with moderate tunneling can result in the highest value of RIC.

DOI
10.1016/j.rio.2025.100880

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The density matrix theory models the refractive index change in a double quantum dot (DQD) system. The orthogonalized plane wave (OPW) is considered for wetting layer (WL)-quantum dot (QD) transitions, and the transition momenta are calculated. The modeling here considers all possible QD-QD and WL-QD transitions, which is another key property of this work. The results show that the tunneling increment raises the refractive change (RIC) to a huge value. Reducing the probe field enables the superluminal propagation of light, which is of viable importance in optical applications. A weaker probe or a strong pump with moderate tunneling can result in the highest value of RIC.
In this work, the energy levels and wave functions of the pyramidal quantum dot (PQD) are numerically calculated using the finite element method. Then, the refractive index changes (RICs) and absorption coefficients (ACs) are determined. To this goal, we have used the compact-density matrix method. Numerical results have been presented for the GaAs/Al[Formula: see text]Ga[Formula: see text]As pyramid quantum dot. It is found that the change of structural parameters like quantum dot sizes has an important influence on energy levels, wave functions, and optical properties of PQD. With increasing the height of PQD, the Acs, and RICs increase and shift toward higher energies.
Second-order nonlinear susceptibility (SONS) in a ladder-plus-Y double quantum dot structure was modeled and then studied numerically under the application of an electric field. The density matrix theory was used to formulate the system while the orthogonalized plane waves for wetting layer-quantum dot (WL-QD) were considered to state the momentum matrix elements for this system. It is found that the momenta follow the smallest energy difference between states with an obvious overlap of the mediated states. Since WL-QD momenta are small, neglecting WL gives high SONS. Millimeter waves are predicted, and a huge SONS can be obtained by the application of more optical fields, which is important in medical and biological applications. The possibility of changing light speed between subluminal and superluminal was predicted here. This opens the way for many applications like multichannel waveguide-multichannel quantum information processing, real quality imaging, and temporal clock.
A model of the dynamical equations of the density matrix describes double tunnelling between double quantum dot (QD) system states, this is to study Kerr nonlinearity in QD structure. Inhomogeneity in the QD system is included which is not included in earlier studies of Kerr nonlinearity in QDs. Possibilities of subluminal and superluminal light propagation and switching between them are examined. Double tunnelling is shown to obtain giant Kerr dispersion compared with single tunnelling. High conduction- and low valence-band tunnelling components are required to obtain high Kerr dispersion. Working with one tunnel component reduced Kerr dispersion and switching between subluminal and superluminal can be obtained and the EIT window can be removed.
Abstract In this letter, we proposed a brand-new version for investigating the optical bistability (OB) and optical multistability (OM) through electron tunneling impact in a defect one-dimensional photonic crystal (1DPC). The defect layer of 1DPC is doped with double quantum dot (DQD) nanostructure which interacts with an indirect incoherent pump and a susceptible probe incident light, respectively. By the usage of the quantum mechanical density matrix method, we first examine the refractive index properties of the defect layer through electron tunneling and indirect incoherent pumping effects. Then, through the usage of the transfer matrix methods, we acquire the reflection and transmission coefficients of the defect 1DPC. At the end, we discuss the OB and OM properties of the reflected and transmitted lighting in negative refractive index situation of the DQD. We determine that during a few parametric conditions the switching from OB to OM or vice versa is feasible for reflected and transmitted light beams.
Abstract In this paper, we have proposed a new model based on the electron tunneling effect for controlling the optical bistability (OB) and optical multistability (OM) in a defect slab structure with a quantum dot molecule (QDM). Due to the presence of the electron tunneling effect, an additional weak signal beam can be generated in the system which makes the medium becomes phase dependent. We have studied the refractive index properties of the QDM via optical susceptibility of the propagated probe light. We have discussed the relative phase effect on negative refractive index (NRI) of the QDM nanostructure due to presence of electron tunneling. Then, by using the transfer matrix method, we have studied the transmission coefficient for NRI of the QDM nanostructure. Then, we have investigated the properties of transmitted light versus incident light for realizing the OB and OM. We have considered the relative phase effect on OB and OM properties of the transmitted beam and find that the switching between them is possible when electron tunneling is present in the quantum dot. Moreover, the optical thickness of the defect layer is also investigated on OB and OM in resonance and non-resonance conditions.
Quantum entropy in a ladder-plus-Y double quantum dot system was calculated. The controlling parameters that are examined are four coherent optical fields, three tunneling components, and incoherent optical pumping. This work differs from others by the inclusion of a wetting layer (WL) and the calculation of momenta for each transition. The results showed that the entropy depends on the difference between the carrier occupations in the states of these two quantum dots (QDs). It is also shown that the probe optical field reduces the entropy, while the pumping field increases it. Turning off the main tunneling component removes the entropy, while high WL-QD momentum increases the entropy. Taking the same value of momentum for all transitions (the case of other works) underestimates the entropy.