Single- and few-particle states in core-shell nanowire quantum dots

Abstract

The electronic properties of single and few-particles in core-shell nanowire quantum dots (NWQD) are investigated. By performing configuration interaction (CI) calculations we particularly elucidate how elevated symmetry character (C 3v or D 2d ) exhibited by single particle orbitals enhances the phase coherence of exciton-photon wavefunction though suppressing spin flip processes. Detailed calculations presented here demonstrate how strain-induced potentials manipulate the symmetry characters, intrinsic oscillator strength and electron-hole dipole in NWQDs. An orbital-dependent kinetic energy is defined based on single particle dispersion and orbital spreadout in k-space. It is shown the exchange occurring between this kinetic energy and strain-induced potentials is responsible for orbital distortions, and thus the energy reordering of different direct and correlation terms. Various structures have been examined to elaborate on the influence of size and orientation together with axial and lateral symmetry of NWQDs. Our many-body calculations suggest that binding energies of s-shell few particle resonances 0 X ± and XX 0 are suppressed when axial and lateral localizations become comparable. Then exerting an external perturbation may renormalize the binding energies, realizing a transition from anti-binding to binding regime or reverse. In this regard, we specifically show that kinetic energy of single particles, and thus correlation energies of associated complexes, exposed to an electric field remain relatively unaffected and the interplay between direct Coulomb terms reorders the multiexcitonic resonances. Sub-µeV fine structure splitting along with the tunable XX 0 binding energy offers NWQDs promising for generating entangled photons in both regular and time reordering schemes.Single and Few-Particle States in Core-Shell NWQDs Temperature (K) −2 1 2 1 0.5 e J τ = → 2 1 0.5 e J τ = → → 0.5 h J τ =−2 1 → 0.5 h J τ =−2 1

Two-Photon Absorption in CdSe Colloidal Quantum Dots Compared to Organic Molecules

“…Computational modeling based on TD-DFT has already been shown as a reliable tool in studies of optical properties of small size (<2 nm) QDs with the main focus on the effect of various passivating ligands − on radiative , and nonradiative , photoexcited processes in CdSe QDs. More accurate many-body methods have also been used in studies of optical properties of various small QDs, including coupled cluster, configuration interaction, and multiconfigurational self-consistent field methods. Being reasonably accurate in inclusion of electron–electron and electron–hole correlations, these methods, unfortunately, are computationally demanding and cannot be yet applied to the QD systems containing more than 50 atoms, especially when most of these atoms are transition metals and heavy elements such as Cd.…”

Toward tripartite hybrid entanglement in quantum dot molecules

“…The QD diameter and its vertical aspect ratio, a h = h D /D D , are chosen as 20 nm and 0.25, respectively. This ratio leads to comparable mutual interactions between electrons and holes, thus the multiparticle states accumulate less correlation energy [13]. The interdot spacing D s determines the wave function symmetry of the hole particle ground state |h 0 and the sign of its tunneling matrix element t h to hop up to the first excited state |h 1 .…”

“…The Galium intermixing in the QD composition facilitates both hybridization and interdot diffusion of the electron and hole. As implied from its dispersion, the electron orbital is stiff against electric field variations, otherwise it would gain considerable kinetic energy [13]; see figure 3(c). Thus |e 0 ≡ |e s 1 and |e 1 ≡ |e s 2 orbitals sustain their spreadout over both QDs maintaining the interdot coupling, |e 0 = |s e,L + |s e,R and |e 1 = |s e,L − |s e,R .…”

“…The Galium intermixing in the QD composition facilitates both hybridization and interdot diffusion of the electron and hole. As implied from its dispersion, the electron orbital is stiff against electric field variations, otherwise it would gain considerable kinetic energy [13]; see Figure 3(c S-shell electron and hole energies undergo an anticrossing in proximity to E z = 0; see Figure 3(d). In accordance with trivial orbital deformations, the s-shell electron energies experience relatively small variations as compared to the s-shell hole energies.…”

“…Since the entangled degree of freedom is mostly defined based on the polarization of a photon (or the spin state of a carrier), this color distinguishability reduces the degree of entanglement, even in a bipartite system. Current solutions offered to establish the coincidence in the energy of photons are often perturbational [3,[7][8][9][10] or architectural [11][12][13], allowing for the creation of up to bipartite quantum correlated states. Actualizing higher order entangled states, however, seems unlikely in a single QD due to the absence of more than two color-matching excitons X in its optical spectrum [14].…”