Query: Highly indistinguishable and strongly entangled photons from symmetric GaAs quantum dots

Candidate papers:

abstract: The development of scalable sources of non classical light is fundamental to unlocking the technological potential of quantum photonics. Semiconductor quantum dots are emerging as near optimal sources of indistinguishable single photons. However, their performance as sources of entangled photon pairs are still modest compared to parametric down converters. Photons emitted from conventional Stranski Krastanov InGaAs quantum dots have shown non optimal levels of entanglement and indistinguishability. For quantum networks, both criteria must be met simultaneously. Here, we show that this is possible with a system that has received limited attention so far: GaAs quantum dots. They can emit triggered polarization entangled photons with high purity (g(2)(0) 0.002+ 0.002) high indistinguishability (0.93+ 0.07 for 2 ns pulse separation) and high entanglement fidelity (0.94+ 0.01) Our results show that GaAs might be the material of choice for quantum dot entanglement sources in future quantum technologies.
author_names: Daniel Huber

Marcus Reindl

Yongheng Huo

Huiying Huang

Johannes S Wildmann

Oliver G Schmidt

Armando Rastelli

Rinaldo Trotta
title: Highly indistinguishable and strongly entangled photons from symmetric GaAs quantum dots
venue: Nature communications
year: 2017

abstract: The generation and long haul transmission of highly entangled photon pairs is a cornerstone of emerging photonic quantum technologies, with key applications such as quantum key distribution and distributed quantum computing. However, a natural limit for the maximum transmission distance is inevitably set by attenuation in the medium. A network of quantum repeaters containing multiple sources of entangled photons would allow to overcome this limit. For this purpose, the requirements on the source's brightness and the photon pairs' degree of entanglement and indistinguishability are stringent. Despite the impressive progress made so far, a definitive scalable photon source fulfilling such requirements is still being sought for. Semiconductor quantum dots excel in this context as sub poissonian sources of polarization entangled photon pairs. In this work we present the state of the art set by GaAs based quantum dots and use them as a benchmark to discuss the challenges to overcome towards the realization of practical quantum networks.
author_names: Christian Schimpf

Marcus Reindl

Francesco Basso Basset

Klaus D Jons

Rinaldo Trotta

Armando Rastelli
title: Quantum dots as potential sources of strongly entangled photons for quantum networks
year: 2020

abstract: Semiconductor quantum dots are converging towards the demanding requirements of photonic quantum technologies. Among different systems, quantum dots with dimensions exceeding the free exciton Bohr radius are appealing because of their high oscillator strengths. While this property has received much attention in the context of cavity quantum electrodynamics, little is known about the degree of indistinguishability of single photons consecutively emitted by such dots and on the proper excitation schemes to achieve high indistinguishability. A prominent example is represented by GaAs quantum dots obtained by local droplet etching, which recently outperformed other systems as triggered sources of entangled photon pairs. On these dots, we compare different single photon excitation mechanisms, and we find (i) a "phonon bottleneck" and poor indistinguishability for conventional excitation via excited states and (ii) photon indistinguishablilities above 90% for both strictly resonant and for incoherent acoustic and optical phonon assisted excitation. Among the excitation schemes, optical phonon assisted excitation enables straightforward laser rejection without a compromise on the source brightness together with a high photon indistinguishability.
author_names: Marcus Reindl

J Weber

Daniel Huber

Christian Schimpf

Saimon Filipe Covre da Silva

Simone Luca Portalupi

Rinaldo Trotta

Peter Michler

Armando Rastelli
title: Highly indistinguishable single photons from incoherently excited quantum dots
venue: Physical Review B
year: 2019

abstract: The generation and long haul transmission of highly entangled photon pairs is a cornerstone of emerging photonic quantum technologies with key applications such as quantum key distribution and distributed quantum computing. However, a natural limit for the maximum transmission distance is inevitably set by attenuation in the medium. A network of quantum repeaters containing multiple sources of entangled photons would allow overcoming this limit. For this purpose, the requirements on the source's brightness and the photon pairs' degree of entanglement and indistinguishability are stringent. Despite the impressive progress made so far, a definitive scalable photon source fulfilling such requirements is still being sought after. Semiconductor quantum dots excel in this context as sub Poissonian sources of polarization entangled photon pairs. In this work, we present the state of the art set by GaAs based quantum dots and use them as a benchmark to discuss the challenges toward the realization of practical quantum networks.
author_names: Christian Schimpf

Marcus Reindl

Francesco Basso Basset

Klaus D Jons

Rinaldo Trotta

Armando Rastelli
title: Quantum dots as potential sources of strongly entangled photons: Perspectives and challenges for applications in quantum networks
year: 2021

abstract: Semiconductor quantum dots (QDs) obtained by epitax ial growth are regarded as one of the most promisin g olid state sources of triggered single and entangled photons f r applications in emerging quantum technologies. While most of the studies presented so far have mos tly focused on InGaAs/GaAs QDs obtained by the Stra nskiKrastanow (SK) growth mode, GaAs QDs in AlGaAs matr ix have emerged as a promising alternative to SK QD s. In this talk I will begin by briefly discussing the growth of GaAs QDs with highly symmetric shape [1 using two independent molecular beam epitaxy machines. I will the n present recent results on the generation of polar ization entangled photons from such dots [2] The good degree of ind istinguishability of the emitted photons recently a lowed us to perform two photon interference experiments using two inde pendent QDs [3] For this experiment the emission energy of one of the QDs was finely tuned by piezoelectric induced strai n. Finally I will show that the addition of strain after growth allows us to substantially modify the nature of confined holes i n a QD, which results in novel selection rules. In particular, uniaxial stress allows the quantization axis of the QD to be reorie nted in the growth plane [4] a configuration parti cularly suitable for integrated quantum photonics applications.
author_names: Armando Rastelli
title: Droplet etched GaAs/AlGaAs quantum dots for quantum photonics applications
year: 2018

abstract: A semiconductor quantum dot (QD) can generate highly indistinguishable single photons at a high rate. For application in quantum communication and integration in hybrid systems, control of the QD optical properties is essential. Understanding the connection between the optical properties of a QD and the growth process is therefore important. Here, we show for GaAs QDs, grown by infilling droplet etched nanoholes, that the emission wavelength, the neutral to charged exciton splitting, and the diamagnetic shift are strongly correlated with the capture zone area, an important concept from nucleation theory. We show that the capture zone model applies to the growth of this system even in the limit of a low QD density in which atoms diffuse over \ensuremath{\mu}\mathrm{m} distances. The strong correlations between the various QD parameters facilitate preselection of QDs for applications with specific requirements on the QD properties; they also suggest that a spectrally narrowed QD distribution will result if QD growth on a regular lattice can be achieved.
author_names: Matthias Christian Lobl

Liang-Jun Zhai

Jan-Philipp Jahn

Julian Ritzmann

Yongheng Huo

Andreas Dirk Wieck

Oliver G Schmidt

Arne Ludwig

Armando Rastelli

Richard John Warburton
title: Correlations between optical properties and Voronoi cell area of quantum dots
venue: Physical Review B
year: 2019

abstract: Introduction Semiconductor quantum dot (QD) is one of the promising candidates for on demand entangled photon emitters. To realize the entangled photon emission on the polarization basis, formation of laterally symmetric QDs are essentially necessary. By using GaAs (111)A surface with three fold rotational symmetry, we have realized highly symmetric GaAs QDs/AlGaAs by droplet epitaxy [1] which generate high quality entangled photon with filtering free violation of Bell's inequality [2] Previously, we have used optical excitation for the entangled photon generation. In this study, we report the formation of light emitting diodes (LED) that generate entangled photons by current injection, which is an important step for practical device applications. Experimental The sample was grown on nGaAs(111)A by solid source molecular beam epitaxy. After the growth of 50 nm n GaAs (Si: 1 x 10 cm) 100 nm n Al0.32Ga0.68As (Si: 5 x 10 cm) 20 nm Al0.33Ga0.67As, and 100 nm Al0.28Ga0.72As at 510 degC, GaAs QDs were formed by droplet epitaxy. To form the QDs, 0.05 monolayers (ML) gallium (0.01 ML/s) were supplied at 450 degC. Then, an As4 flux (5 x 10 Torr) was supplied at 200 degC for crystallization, followed by annealing at 500 degC. The QDs were capped with 100 nm Al0.28Ga0.72As and 25 nm Al0.33Ga0.67As at 510 degC. Then, a 100 nm p Al0.33Ga0.67As (Si: 5 x 10 cm) 20 nm p Al0.33Ga0.67As (Si: 2 x 10 cm) and 20 nm p GaAs (Si: 2 x 10 cm) were grown at 580 degC. For the growth of n type (and undoped) and p type layers, high (7 x 10 Torr) and low (6 x 10 Torr) As4 fluxes were used, respectively, to control the Si doping sites. After the growth, bottom (Au/Ni/AuGe) and top (Au/Pt/Ti) contact electrodes were formed, followed by annealing at 350degC. The electroluminescence was obtained from the 10 x 10mm apertures formed in the top contact electrode. Results and Discussions The I V curve of the sample revealed a diode type asymmetric response. We applied a forward bias, so that the electroluminescence intensity reaches the saturation value. Figure 1(a) shows coincidence histograms for the biexcitonic photons (XX) and the excitonic photons (X) with circular polarizations setting. The presence of a central peak for cross circular polarization confirms a higher probability than that for detecting uncorrelated photons. The central peak disappears for co circular polarization. Figure 1(b) shows coincidence histograms for linear polarizations setting. A positive correlation appears for the parallel polarization, while it disappears for the orthogonal polarizations. The XX and X photons are clearly correlated in any polarization basis, which is a rigorous proof for the formation of quantum entanglement. [1] T. Mano et al. Appl. Phys. Express 3, 065203 (2010) [2] T. Kuroda et al. Phys. Rev. B 88, 041306(R) (2013) Fig. 1 Coincidence histogram between excitons and biexciton photons for different polarization combinations. 500
author_names: Neul Ha

Takaaki Mano

Yoshiki Sakuma

Kazuaki Sakoda

Takashi Kuroda
title: Entangled photon emitting diode based on GaAs droplet quantum dots
year: 2016

abstract: Entangled photons are efficiently generated from highly symmetric, site controlled InGaAs/GaAs quantum dots grown in inverted pyramids. Fine structure splitting of the intermediate exciton level is suppressed without the application of electric, magnetic or strain fields. Polarization entanglement is demonstrated by measurements of the two photon density matrix and the confirmation of several entanglement criteria.
author_names: Aneena Mohan

Marco Felici

Pascal Gallo

Benjamin Dwir

Alok P Rudra

Jerome Faist

E Kapon
title: Polarization entangled photons produced with high symmetry site controlled quantum dots
year: 2010

abstract: To generate entangled photon pairs via quantum dots (QDs) the exciton fine structure splitting (FSS) must be comparable to the exciton homogeneous line width. Yet in the (In,Ga)As/GaAs QD, the intrinsic FSS is about a few tens meV. To achieve photon entanglement, it is necessary to Cherrypick a sample with extremely small FSS from a large number of samples, or to apply strong in plane magnetic field. Using theoretical modeling of the fundamental causes of FSS in QDs, we predict that the intrinsic FSS of InAs/InP QDs is an order of magnitude smaller than that of InAs/GaAs dots, and better yet, their excitonic gap matches the 1.55 mm fiber optic wavelength, therefore offer efficient on demand entangled photon emitters for long distance quantum communication.
author_names: Lixin He

Ming Gong

Chuan-Feng Li

Guangcan Guo

Alex Zunger
title: J un 2 00 8 Highly reduced Fine structure splitting in InAs InP quantum dots offering efficient on demand 1 55 m m entangled photon emitter
year: 2018

abstract: The generation of high quality entangled photon pairs has been a long sought goal in modern quantum communication and computation. So far, the most widely used entangled photon pairs have been generated from spontaneous parametric down conversion (SPDC) a process that is intrinsically probabilistic and thus relegated to a regime of low rates of pair generation. In contrast, semiconductor quantum dots can generate triggered entangled photon pairs through a cascaded radiative decay process and do not suffer from any fundamental trade off between source brightness and multi pair generation. However, a source featuring simultaneously high photon extraction efficiency, high degree of entanglement fidelity and photon indistinguishability has been lacking. Here, we present an entangled photon pair source with high brightness and indistinguishability by deterministically embedding GaAs quantum dots in broadband photonic nanostructures that enable Purcell enhanced emission. Our source produces entangled photon pairs with a pair collection probability of up to 0.65(4) (single photon extraction efficiency of 0.85(3) entanglement fidelity of 0.88(2) and indistinguishabilities of 0.901(3) and 0.903(3) (brackets indicate uncertainty on last digit) This immediately creates opportunities for advancing quantum photonic technologies.Embedding GaAs quantum dots in broadband photonic nanostructures allows a source of entangled photons to be fabricated with simultaneous enhancements of the most important parameters.
author_names: Jin Liu

Rongbin Su

Yuming Wei

Beimeng Yao

Saimon Filipe Covre da Silva

Ying Yu

Jake Iles-Smith

Kartik Srinivasan

Armando Rastelli

Juntao Li

Xuehua Wang
title: A solid state source of strongly entangled photon pairs with high brightness and indistinguishability
venue: Nature Nanotechnology
year: 2019