Single-photon generation from self-assembled GaAs/InAlAs(111)A quantum dots with ultrasmall fine-structure splitting (original) (raw)
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Exciton fine structure splitting of single InGaAs self-assembled quantum dots
Physica E: Low-dimensional Systems and Nanostructures, 2004
We show how the resonant absorption of the ground state neutral exciton conÿned in a single InGaAs self-assembled quantum dot can be directly observed in an optical transmission experiment. A spectrum of the di erential transmitted intensity is obtained by sweeping the exciton energy into resonance with laser photons exploiting the voltage induced Stark-shift. We describe the details of this experimental technique and some example results which exploit the ∼1 eV spectral resolution. In addition to the ÿne structure splitting of the neutral exciton and an upper bound on the homogeneous linewidth at 4:2 K, we also determine the transition electric dipole moment. ?
Physical Review B, 2012
We investigate the vertical electric field tuning of the exciton fine structure splitting (FSS) in several InGaAs and GaAs quantum dots (QDs) using the atomistic empirical pseudopotential approach and configuration interaction. We find that the FSS is surprisingly tunable, with a rate similar to the one reported for lateral electric fields. The minimum FSS for GaAs QDs often lies below the radiative linewidth, which makes them good candidates for the generation of entangled photon pairs. We highlight, however, that random alloy fluctuations affect the minimum FSS by ± 1.4 µeV, so that a post-selection of QDs may still be beneficial to obtain entangled photon pairs with the highest fidelity. We suggest a simple experimental procedure for this task. The FSS is therefore a rare observable, where the specific decoration of the random alloy lattice, significantly matters.
Self-assembled quantum dots as a source of single photons and photon pairs
physica status solidi (b), 2003
We investigate the emission from a single self-organised InAs/GaAs quantum dots as a potential single or pair photon source. Single photon emission is stimulated by exciting the dot with ps laser pulses and collecting either the exciton or biexciton emission line. A more convenient and practical arrangement is to excite the quantum dot electrically by growing it inside a p-in structure. Photon pairs are generated through collecting both the exciton and biexciton emissions. We show a strong correlation in the emission times of the exciton and biexciton photon from the dot, as well as in their linear polarisations.
ACS Nano, 2015
Fine-structure splitting (FSS) of excitons in semiconductor nanostructures is a key parameter that has significant implications in photon entanglement and polarization conversion between electron spins and photons, relevant to quantum information technology and spintronics. Here, we investigate exciton FSS in self-organized lateral InAs/GaAs quantum-dot molecular structures (QMSs) including laterally-aligned double quantum dots (DQDs), quantum-dot clusters (QCs) and quantum rings (QRs), by employing polarization-resolved micro-photoluminescence (µPL) spectroscopy. We find a clear trend in FSS between the studied QMSs depending on their geometric arrangements, from a large FSS in the DQDs to a smaller FSS in the QCs and QRs. This trend is accompanied by a corresponding difference in the optical polarization directions of the excitons between these QMSs, namely, the bright-exciton lines are linearly polarized preferably along or perpendicular to the [11 ̅ 0] crystallographic axis in the DQDs that also defines the alignment direction of the two constituting QDs, whereas in the QCs and QRs the polarization directions are
In(Ga)As/GaAs quantum dots grown on a (111) surface as ideal sources of entangled photon pairs
Physical Review B, 2009
Self-organized In͑Ga͒As/GaAs quantum dots ͑QDs͒ grown on ͑111͒ substrate are proposed as ideal sources for the generation of entangled photon pairs. Due to the threefold rotational symmetry of the ͑111͒ surface, QDs with C 3v symmetry or higher are expected to develop during growth. In contrast to QDs on ͑001͒-oriented substrates, the symmetry of the confinement potential of ͑111͒ QDs is not lowered by piezoelectric effects. As a result the excitonic bright splitting vanishes and the biexciton→ exciton→ 0 recombination cascade can be used for the generation of entangled photons. We evaluate the spectroscopic separability of excitonic and biexcitonic emissions as a function of QD size, shape, and composition using the configuration-interaction model in conjunction with eight-band k • p theory. The piezoelectric field in ͑111͒ QDs predominantly aligns along the growth direction and gives rise to vertical charge separation. First-and second-order piezoelectric fields are oriented in opposite directions. The In/Ga ratio inside the QD determines the leading contribution and can be employed to balance both terms in order to achieve a field-free situation with maximal electron-hole overlap. The biexciton binding energy depends on the net piezoelectric potential drop across the QD vertical extension and becomes maximal if the first-and second-order fields outweigh each other within the QD interior.
Nature communications, 2012
Semiconductor quantum dots are potential sources for generating polarization-entangled photons efficiently. The main prerequisite for such generation based on biexciton-exciton cascaded emission is to control the exciton fine-structure splitting. Among various techniques investigated for this purpose, an electric field is a promising means to facilitate the integration into optoelectronic devices. Here we demonstrate the generation of polarization-entangled photons from single GaAs quantum dots by an electric field. In contrast to previous studies, which were limited to In(Ga)As quantum dots, GaAs island quantum dots formed by a thickness fluctuation were used because they exhibit a larger oscillator strength and emit light with a shorter wavelength. A forward voltage was applied to a Schottky diode to control the fine-structure splitting. We observed a decrease and suppression in the fine-structure splitting of the studied single quantum dot with the field, which enabled us to gene...
Single-photon emitters based on epitaxial isolated InP/InGaP quantum dots
Applied Physics Letters, 2012
Quantum dots as single-photon sources have several advantages, such as emitting light over a broad spectral range and being photostable. Quantum dots with densities as low as 1 dot/µm 2 have been achieved using ultra-low-rate epitaxy and single-dot emission measured without apertures or post-growth processing.
Quantum Dots for Single- and Entangled-Photon Emitters
IEEE Photonics Journal, 2009
The efficient generation of polarized single or entangled photons is a crucial requirement for the implementation of quantum key distribution (QKD) systems. Selforganized semiconductor quantum dots (QDs) are capable of emitting one polarized photon or an entangled photon pair at a time using appropriate electrical current injection. We realized a highly efficient single-photon source (SPS) based on well-established semiconductor technology: In a pin structure, a single electron and a single hole are funneled into a single InAs QD using a submicron AlO x current aperture. Efficient radiative recombination leads to emission of single polarized photons with an all-time record purity of the spectrum. Non-classicality of the emitted light without using additional spectral filtering is demonstrated. The out-coupling efficiency and the emission rate are increased by embedding the SPS into a micro-cavity. The design of the micro-cavity is based on detailed modeling to optimize its performance. The resulting resonant single-QD diode is driven at a repetition rate of 1 GHz, exhibiting a second-order correlation function of g ð2Þ ð0Þ ¼ 0. Eventually, QDs grown on (111)-oriented substrates are proposed as a source of entangled photon pairs. Intrinsic symmetry-lowering effects leading to the splitting of the exciton bright states are shown to be absent for this substrate orientation. As a result, the XX ! X ! 0 recombination cascade of a QD can be used for the generation of entangled photons without further tuning of the fine-structure splitting via QD size and/or shape.