Coulomb Mediated Hybridization of Excitons in Coupled Quantum Dots

Abstract

We report the Coulomb mediated hybridization of excitonic states in an optically active, artificial quantum dot molecule. By probing the optical response of the artificial molecule as a function of the static electric field applied along the molecular axis, we observe unexpected avoided level crossings that do not arise from the dominant single particle tunnel coupling. We identify a new few-particle coupling mechanism stemming from Coulomb interactions between different neutral exciton states. Such Coulomb resonances hybridize the exciton wave function over four different electron and hole single-particle orbitals. Comparisons of experimental observations with microscopic 8-band k · p calculations taking into account a realistic quantum dot geometry show good agreement and reveal that the Coulomb resonances arise from broken symmetry in the artificial molecule.Understanding and controlling the fundamental interactions that couple discrete quantum states lies at the very heart of applied quantum science. For example, couplings between distinct physical subsystems mediated by the Coulomb interaction can be used to entangle qubits electrostatically [1], to build single-photon transistors on the basis of Förster resonances [2] or to control resonant energy transfer [3]. Strong tunnel couplings between proximal quantum dots have been shown to facilitate electrical and optical spin-qubit operations [4,5] while long range magnetic dipolar interactions have been exploited for prototype quantum registers [6]. Thus the nature of quantum couplings has been under extensive investigation for many prototypical quantum systems. Examples include naturally occurring atoms [3,7,8] and defect centers [9,10] as well as artificial atoms and molecules [11][12][13]. Due to advanced nanostructure fabrication techniques [14,15] and efficient coupling to light [16,17], artificial molecules consisting of pairs of semiconductor quantum dots (QDs) have emerged as ideal prototypical solid-state systems to investigate and electrically control interactions between proximal quantum systems [11,12].By embedding a QD-molecule into the intrinsic region of a diode structure, exciton states in the different QDs can be tuned into and out of resonance by controlling the electric field along the growth direction [11,12]. The fundamental signatures of quantum couplings are avoided level crossings in the electronic energy level structure of a QD-molecule as single particle states are tuned in and out of resonance [18]. The importance of Coulomb interactions has been pointed out for the form and position of resonances in QD-molecule systems [19][20][21]. However, single particle tunneling that either hybridizes single electrons or holes remains the dominant coupling mechanism in these cases [11][12][13][22][23][24][25]. Most recently another resonant coupling mechanism with an inherently two particle nature has been predicted theoretically that entirely relies on the Coulomb mediated interaction between two different exciton states [26]. In strong contra...

Self‐Assembled InAs/GaAs Coupled Quantum Dots for Photonic Quantum Technologies

“…The use of this technique has resulted in extremely uniform QD heights and as a result very narrow ensemble linewidths . This technique will also often produce flat QDs whose shape resembles a disk, truncated lens, or truncated pyramid, and a nonuniform profile of alloy composition, with a higher indium concentration in the center of each QD forming an inverted cone or trumpet distribution …”

Excitonic States and Photoluminescence Spectra of a Quantum Dot Molecule Exposed to the External Static Electric Field

“…Ardelt et al measured the optical response of an individual quantum dot molecule as a function of the static electric field directed along the symmetry axis. They observed the set of the avoided level crossing which can be described using eight‐band theory with a realistic quantum dot geometry when Coulomb interaction is taken into account.…”

Polaron resonances in two vertically stacked quantum dots

“…2(a) these resonance structures are marked by E1,E2 (electron tunneling resonance), H1,H2 (hole tunneling) and EH (very weak coupling between two indirect configurations). We note that extending the basis would lead to a more complex pattern including Coulomb resonances 18,21 . Fig.…”

“…In particular, a double quantum dot (DQD) structure supports spatially direct and indirect states with different dipole moments, the energy of which can be tuned in a broad range by applying an axial electric field [13][14][15][16][17] . Recently, the spectrum of such a system was mapped out by combined spectroscopy techniques and successfully modeled using an 8-band k·p theory in the envelope-function approximation 18 . The electric-field tunability of energy levels in such systems might allow one to study the polaron resonances as a function of the electric field by matching various energy shells of the two dots, which offers much more flexibility in comparison to the single-QD studies, where only limited tunability by magnetic field is available 3,4 .…”