Optical pumping of charged excitons in unintentionally doped InAs quantum dots

As an alternative to commonly used electrical methods, we have investigated the optical pumping of charged exciton complexes addressing impurity related transitions with photons of the appropriate energy. Under these conditions, we demonstrate that the pumping fidelity can be very high while still maintaining a switching behavior between the different excitonic species. This mechanism has been investigated for single quantum dots of different size present in the same sample and compared with the direct injection of spectator electrons from nearby donors.Comment: 4 pages and 3 figures submitted to AP

Nano

Transformant el món amb la Nanotecnociènci

Creativitat al servei del futur. El nou impuls de la Nanotecnociència

Creativity at the Service of Future Progress: New Boom in Nanotechnoscience.Currently, a host of research-project applications contain the prefi x nano. However, this could be more-closely related to a new industrial explosion than with the emergence of new conceptual proposals. Society has also been touched by the euphoria that, in some cases, could be called a “craze”- but proposals from the most cautious sectors are far from science fi ction. Among these we fi nd Biomimetics, which takes as a reference point the solutions that living beings have adopted during the evolutionary process. By uniting these technical and academic visions we generate a third more realistic view of these pet hates. Perhaps this is an alternative that provides collective genius creatively and possibly sustainably at the service of future developments

El majúscul impacte d'allò minúscul

Tininess Makes a Huge Impact: Semiconducting and Metallic Nanoparticles.Defying the conventions of linguistic repetition, the prefi x nano springs up in all languages with unusual force. Nanostructure, nanofi ber, nanocrystals, nanowires, nanotubes, nanodevice ... These are just a few examples, although you won’t fi nd them in the dictionary. These words have retained some meaning of the root from which they are derived, but should inescapably be contemplated, at best, as distant metaphorical refl ections. The words nanoparticle and nanocrystal will be the focus of this article: What are nanoparticles? When is a nanoparticle a nanocrystal? When is the nanoparticle a quantum dot? What applications can we expect if they are semiconducting or metallic

Optical characterization of individual GaAs quantum dots grown with height control technique

We show that the epitaxial growth of height-controlled GaAs quantum dots, leading to the reduction of the inhomogeneous emission bandwidth, produces individual nanostructures of peculiar morphology. Besides the height controlled quantum dots, we observe nanodisks formation. Exploiting time resolved and spatially resolved photoluminescence we establish the decoupling between quantum dots and nanodisks and demonstrate the high optical properties of the individual quantum dots, despite the processing steps needed for height control.Sarti, F.; Muñoz Matutano, G.; Bietti, S.; Vinattieri, A.; Sanguinetti, S.; Gurioli, M. (2013). Optical characterization of individual GaAs quantum dots grown with height control technique. Journal of Applied Physics. 114(2):1243011-1243014. doi:10.1063/1.4821901S124301112430141142Shields, A. J. (2007). Semiconductor quantum light sources. Nature Photonics, 1(4), 215-223. doi:10.1038/nphoton.2007.46Koguchi, N. (1993). New selective molecular-beam epitaxial growth method for direct formation of GaAs quantum dots. Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 11(3), 787. doi:10.1116/1.586789Watanabe, K., Koguchi, N., & Gotoh, Y. (2000). Fabrication of GaAs Quantum Dots by Modified Droplet Epitaxy. Japanese Journal of Applied Physics, 39(Part 2, No. 2A), L79-L81. doi:10.1143/jjap.39.l79Sanguinetti, S., & Koguchi, N. (2013). Droplet epitaxy of nanostructures. Molecular Beam Epitaxy, 95-111. doi:10.1016/b978-0-12-387839-7.00004-xKeizer, J. G., Bocquel, J., Koenraad, P. M., Mano, T., Noda, T., & Sakoda, K. (2010). Atomic scale analysis of self assembled GaAs/AlGaAs quantum dots grown by droplet epitaxy. Applied Physics Letters, 96(6), 062101. doi:10.1063/1.3303979(s. f.). doi:10.1021/nl048192Lee, J. H., Wang, Z. M., Abuwaar, Z. Y., Strom, N. W., & Salamo, G. J. (2006). Evolution between self-assembled single and double ring-like nanostructures. Nanotechnology, 17(15), 3973-3976. doi:10.1088/0957-4484/17/15/061Somaschini, C., Bietti, S., Koguchi, N., & Sanguinetti, S. (2011). Coupled quantum dot–ring structures by droplet epitaxy. Nanotechnology, 22(18), 185602. doi:10.1088/0957-4484/22/18/185602Somaschini, C., Bietti, S., Koguchi, N., & Sanguinetti, S. (2009). Fabrication of Multiple Concentric Nanoring Structures. Nano Letters, 9(10), 3419-3424. doi:10.1021/nl901493fReyes, K., Smereka, P., Nothern, D., Millunchick, J. M., Bietti, S., Somaschini, C., … Frigeri, C. (2013). Unified model of droplet epitaxy for compound semiconductor nanostructures: Experiments and theory. Physical Review B, 87(16). doi:10.1103/physrevb.87.165406Bietti, S., Somaschini, C., & Sanguinetti, S. (2013). Crystallization kinetics of Ga metallic nano-droplets under As flux. Nanotechnology, 24(20), 205603. doi:10.1088/0957-4484/24/20/205603Jo, M., Mano, T., & Sakoda, K. (2010). Morphological control of GaAs quantum dots grown by droplet epitaxy using a thin AlGaAs capping layer. Journal of Applied Physics, 108(8), 083505. doi:10.1063/1.3493262Ohtake, A. (2008). Surface reconstructions on GaAs(001). Surface Science Reports, 63(7), 295-327. doi:10.1016/j.surfrep.2008.03.001Mano, T., Abbarchi, M., Kuroda, T., Mastrandrea, C. A., Vinattieri, A., Sanguinetti, S., … Gurioli, M. (2009). Ultra-narrow emission from single GaAs self-assembled quantum dots grown by droplet epitaxy. Nanotechnology, 20(39), 395601. doi:10.1088/0957-4484/20/39/395601Adorno, S., Bietti, S., & Sanguinetti, S. (2013). Annealing induced anisotropy in GaAs/AlGaAs quantum dots grown by droplet epitaxy. Journal of Crystal Growth, 378, 515-518. doi:10.1016/j.jcrysgro.2012.11.006Horikoshi, Y., Kawashima, M., & Yamaguchi, H. (1988). Migration-Enhanced Epitaxy of GaAs and AlGaAs. Japanese Journal of Applied Physics, 27(Part 1, No. 2), 169-179. doi:10.1143/jjap.27.16

Divulgando la cultura científica en la ciudad. Asociación cultural "Piratas de la Ciencia"

El movimiento asociativo y las plataformas ciudadanas han sido y continúan siendo uno de los grandes bloques de consolidación del activismo social. Laraña y Gusfield (1994) hablan de un cambio de contexto de los movimientos sociales, desde un ámbito relacionado con el binomio capital-trabajo hacia una movilización por la pluralidad de valores culturales y simbólicos. Este es el caso, por ejemplo, del activismo ecológico, plataformas de defensores de consumidores, pacifistas, entre otros, que buscan formas alternativas para la participación y decisión en asuntos de interés. Sin embargo, no es tan fácil determinar si existe un movimiento social directo originado desde los propios colectivos científicos. El movimiento Open, el 'escéptico' entre periodistas, científicos y divulgadores o las asociaciones en pro de la I+D, podrían entenderse como ejemplos de activismo o de movimiento social. El colectivo Piratas de la Ciencia es una asociación cultural independiente que viene trabajando en el campo de la comunicación de la ciencia en el entorno local e internacional. Las actividades que se proponen en la asociación se entienden como acciones de grupo, colectivas, con un interés social dirigido a promover el contacto entre especialistas, en los distintos escenarios ciudadanos. Particularmente, entendemos al científico como uno más de los actores involucrados en la consolidación de la cultura en los distintos entornos sociales y ciudadanos. Presentaremos un resumen de las actividades realizadas por nuestra asociación en este contexto en los últimos años

All optical switching of a single photon stream by excitonic depletion

Single semiconductor quantum dots have been extensively used to demonstrate the deterministic emission of high purity single photons. The single photon emission performance of these nanostructures has become very well controlled, offering high levels of photon indistinguishability and brightness. Ultimately, quantum technologies will require the development of a set of devices to manipulate and control the state of the photons. Here we measure and simulate a novel all-optical route to switch the single photon stream emitted from the excitonic transition in a single semiconductor quantum dot. A dual non-resonant excitation pumping scheme is used to engineer a switching device operated with GHz speeds, high differential contrasts, ultra-low power consumption and high single photon purity. Our device scheme can be replicated in many different zero dimensional semiconductors, providing a novel route towards developing a platform-independent on-chip design for high speed and low power consumption quantum devices. Using semiconductor quantum dots as single-photon sources for application to quantum technologies is promising due to the high brightness and photon purity of the emitted light. Here, a method of optically switching their emission based on excitonic depletion is presented

All-Optical Fiber Hanbury Brown & Twiss Interferometer to study 1300 nm single photon emission of a metamorphic InAs Quantum Dot

[EN] New optical fiber based spectroscopic tools open the possibility to develop more robust and efficient characterization experiments. Spectral filtering and light reflection have been used to produce compact and versatile fiber based optical cavities and sensors. Moreover, these technologies would be also suitable to study N-photon correlations, where high collection efficiency and frequency tunability is desirable. We demonstrated single photon emission of a single quantum dot emitting at 1300 nm, using a Fiber Bragg Grating for wavelength filtering and InGaAs Avalanche Photodiodes operated in Geiger mode for single photon detection. As we do not observe any significant fine structure splitting for the neutral exciton transition within our spectral resolution (46 mu eV), metamorphic QD single photon emission studied with our all-fiber Hanbury Brown & Twiss interferometer could lead to a more efficient analysis of entangled photon sources at telecom wavelength. This all-optical fiber scheme opens the door to new first and second order interferometers to study photon indistinguishability, entangled photon and photon cross correlation in the more interesting telecom wavelengths.G Munoz-Matutano thanks the Spanish Juan de la Cierva program (JCI-2011-10686). We acknowledge the support of the Spanish MINECO through projects TEC2014-53727-C2-1-R & TEC2014-60378-C2-1-R, the Research Excellency Award Program GVA PROMETEO 2013/012 PROMETEOII/2014/059 and the Explora Ciencia Tecnologia TEC2013-50552-EXP MULTIFUN project, and the Nanoscale Quantum Optics MPNS COST Action MP1403.Muñoz Matutano, G.; Barrera Vilar, D.; Fernandez-Pousa, CR.; Chulia-Jordan, R.; Seravalli. L.; Trevisi, G.; Frigeri, P.... (2016). All-Optical Fiber Hanbury Brown & Twiss Interferometer to study 1300 nm single photon emission of a metamorphic InAs Quantum Dot. Scientific Reports. 6(2721):1-9. https://doi.org/10.1038/srep27214S1962721Walmsley, I. A. 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Size-dependent fine-structure splitting in self-organized InAs/GaAs quantum dots. Phys. Rev. Lett. 95, 257402 (2005).Hadfield, R. H. Single-photon detectors for optical quantum information applications. Nat. Photonics 3, 696–705 (2009).Zinoni, C. et al. Time-resolved and antibunching experiments on single quantum dots at 1300nm. Appl. Phys. Lett. 88, 131102 (2006).Liu, X. et al. Single-photon emission in telecommunication band from an InAs quantum dot grown on InP with molecular-beam epitaxy. Appl. Phys. Lett. 103, 061114 (2013).Benyoucef, M., Yacob, M., Reithmaier, J. P., Kettler, J. & Michler, P. Telecom-wavelength (1.5 μm) single-photon emission from InP-based quantum dots. Appl. Phys. Lett. 103, 162101 (2013).Ward, M. et al. Coherent dynamics of a telecom-wavelength entangled photon source. Nat. Commun. 5, 3316 (2014).Rakher, M. T. et al. Quantum transduction of telecommunications-band single photons from a quantum dot by frequency upconversion. Nat. 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Superradiance Emission and Its Thermal Decoherence in Lead Halide Perovskites Superlattices

Self-assembled nanocrystals (NCs) into superlattices (SLs) are alternative materials to polycrystalline films and single crystals, which can behave very differently from their constituents, especially when they interact coherently with each other. This work concentrates on the Superradiance (SR) emission observed in SLs formed by CsPbBr3 and CsPbBrI2 NCs. Micro-Photoluminescence spectra and transients in the temperature range 4–100 K are measured in SLs to extract information about the SR states and uncoupled domains of NCs. For CsPbBr3 SLs with mostly homogeneous SR lines (linewidth 1–5 meV), this work measures lifetimes as short as 160 ps, 10 times lower than the value measured in a thin film made with the same NCs, which is due to domains of near identical NCs formed by 1000 to 40 000 NCs coupled by dipole–dipole interaction. The thermal decoherence of the SR exciton state is evident above 25 K due to its coupling with an effective phonon energy of ≈8 meV. These findings are an important step toward understanding the SR emission enhancement factor and the thermal dephasing process in perovskite SLs.Financial support from the Spanish Ministry of Science (MICINN) through project no. PID2020- 120484RB-I00 is gratefully acknowledged. G.M.M. also thanks the support from the Spanish MICINN & AEI (project RTI2018-099015-J-I00). I.M.S. thanks the funding of MCIN/AEI/10.13039/501100011033 with the project STABLE PID2019-107314RB-I00. S.G. acknowledges her “Grisolia” grant from Generalitat Valenciana, and G.M.M. thanks the Ramon y Cajal programme (contract RYC2020-030099-I). Thanks are also due to Dr. Raúl Iván Sánchez Alarcón for his help with X-ray diffraction characterization of NC films and SLs