Control of the chemiluminescence spectrum with porous Bragg mirrors

Tunable, battery free light emission is demonstrated in a solid state device that is compatible with lab on a chip technology and easily fabricated via solution processing techniques. A porous one dimensional (1D) photonic crystal (also called Bragg stack or mirror) is infiltrated by chemiluminescence rubrene-based reagents. The Bragg mirror has been designed to have the photonic band gap overlapping with the emission spectrum of rubrene. The chemiluminescence reaction occurs in the intrapores of the photonic crystal and the emission spectrum of the dye is modulated according to the photonic band gap position. This is a compact, powerless emitting source that can be exploited in disposable photonic chip for sensing and point of care applications.Comment: 8 pages, 3 figure

Biexciton initialization by two-photon excitation in site-controlled quantum dots: the complexity of the antibinding state case

In this work, we present a biexciton state population in (111)B oriented site-controlled InGaAs quantum dots (QDs) by resonant two photon excitation. We show that the excited state recombines emitting highly pure single photon pairs entangled in polarization. The discussed cases herein are compelling due to the specific energetic structure of pyramidal InGaAs QDs—an antibinding biexciton—a state with a positive binding energy. We demonstrate that resonant two-photon excitation of QDs with antibinding biexcitons can lead to a complex excitation-recombination scenario. We systematically observed that the resonant biexciton state population is competing with an acoustic-phonon assisted population of an exciton state. These findings show that under typical two-photon resonant excitation conditions, deterministic biexciton state initialization can be compromised. This complication should be taken into account by the community members aiming to utilize similar epitaxial QDs with an antibinding biexciton

Measurements of photo-nuclear jet production in Pb plus Pb collisions with ATLAS

Ultra-peripheral heavy ion collisions provide a unique opportunity to study the parton distributions in the colliding nuclei via the measurement of photo-nuclear jet production. An analysis of jet production in ultra-peripheral Pb+Pb collisions at √sNN = 5.02 TeV performed using data collected with the ATLAS detector in 2015 is described. The data set corresponds to a total Pb+Pb integrated luminosity of 0.38 nb−1. The ultra-peripheral collisions are selected using a combination of forward neutron and rapidity gap requirements. The cross-sections, not unfolded for detector response, are compared to results from Pythia Monte Carlo simulations re-weighted to match a photon spectrum obtained from the STARlight model. Qualitative agreement between data and these simulations is observed over a broad kinematic range suggesting that using these collisions to measure nuclear parton distributions is experimentally realisable

Heavy Ion Results from ATLAS

These proceedings provide an overview of the new results obtained with the ATLAS detector at the LHC, which were presented in the Quark Matter 2017 conference. These results were covered by twelve parallel talks, one flash talk and eleven posters. These proceedings group these results into five areas: initial state, jet quenching, quarkonium production, longitudinal flow dynamics, and collectivity in small systems

Measurements of photo-nuclear jet production in Pb + Pb collisions with ATLAS

Ultra-peripheral heavy ion collisions provide a unique opportunity to study the parton distributions in the colliding nuclei via the measurement of photo-nuclear jet production. An analysis of jet production in ultra-peripheral Pb+Pb collisions at √sNN = 5.02 TeV performed using data collected with the ATLAS detector in 2015 is described. The data set corresponds to a total Pb+Pb integrated luminosity of 0.38 nb⁻¹. The ultra-peripheral collisions are selected using a combination of forward neutron and rapidity gap requirements. The cross-sections, not unfolded for detector response, are compared to results from Pythia Monte Carlo simulations re-weighted to match a photon spectrum obtained from the STARlight model. Qualitative agreement between data and these simulations is observed over a broad kinematic range suggesting that using these collisions to measure nuclear parton distributions is experimentally realisable

Advanced processing strategies for site-controlled pyramidal quantum dots

Today, the world is on the verge of a new technological breakthrough that has been called the “second quantum revolution”: much like the understanding of semiconductor physics paved the way for the development of integrated circuits and ushered the age of information technology, the development of the first working quantum computers might start a profound change in the way we process information, and pave the way for much anticipated technological breakthrough. In my thesis, I have investigated the applications of Pyramidal Quantum Dots (PQDs) as potential sources of single and entangled photons, with a particular focus on improving their quality and brightness, and explored new approaches for their processing that would make them suitable for integration in future quantum devices. In order to address the limits of the conventional InGaAs in GaAs PQDs in relation to resonant pumping of the biexcitonic state, I contributed to the development of two new families of dots: GaAs in AlGaAs PQDs and GaAs dots confined by superlattice barriers. For the former, only results of growths on templates of smaller size were reported in the literature, while the latter is a completely new family of PQDs altogether. Results reported in this thesis indicate a surprising uniformity in spectral features for either family, and demonstrate that resonant excitation can indeed be achieved due to the binding biexcitonic state. In collaboration with Prof. Di Falco’s group in the University of St. Andrews (UK), we have demonstrated potential applications in the field of semiconductor non-classical light sources of the Electron Beam Induced Deposition technique, which allowed us to fabricate complex dielectric nanostructures directly above the quantum emitters. Our work showed how this approach doesn’t cause any significant degradation in the emission spectra, and was complemented by a large number of simulations to elucidate the underlying mechanisms that allow SiO_2 nanostructures to boost light extraction efficiency form the semiconductor matrix depending on their shape. A more promising approach to boost the brightness of our dots was also developed, in the form of a self-aligning technique that allows to fabricate micro and nanopillars using dry etching, and that allowed us to achieve our own record of brightness. Furthermore, an approach to compensate for the effects of the excitonic fine structure splitting on the level of entanglement was devised: the model we have developed complements similar proposals that have previously appeared in the literature, but is also extremely intuitive due to its sequential logic gate structure. Finally, for the first time transmission electron microscopy of PQDs was achieved in a joint effort with Queen’s University Belfast, a success in large part made possible by the new processing strategies devised in this thesis, and whose preliminary results are here reported

Organic and hybrid photonic crystals

Polymer multilayer structures have attracted increasing attention in the recent years because of the straightforward and low-cost techniques that can be used for their fabrication. When the multilayers are composed of a periodical alternation of two materials with different refractive indexes and with layer thicknesses comparable with the wavelength of light, they take the name of distributed Bragg reflectors (DBR). They behave like planar one-dimensional photonic crystals (PhC) and exhibit a photonic band gap (PBG), a spectral region in which photons with suitable energy and wave vector are not allowed to propagate through the crystal. Moreover, within the PBG and at its edges, modifications of radiative photophysical processes occur. The spectral position, efficiency and linewidth of the PBG can be engineered by modifying the layer thicknesses and the refractive indexes of the two materials. While DBRs grown using inorganic materials are well known, polymer and colloidal particle DBRs are receiving a renewed interest due to the possibility to chemically engineer their structural properties and photonic functions; moreover, they can be free-standing and flexible thus being adaptable to any surface. Furthermore, polymers and porous structures can easily embed many other active materials, paving the way to a myriad of applications. In this chapter, we introduce polymer multilayers and planar microcavities fabricated using the spin coating technique, discussing the different materials employed and manufacturing challenges. We will also review different applications that exploit these kinds of photonic structures ranging from lasing to sensing

Towards 3D characterisation of site-controlled InGaAs pyramidal QDs at the nanoscale

In this work, we report an extensive investigation via transmission electron microscopy (TEM) techniques of InGaAs/GaAs pyramidal quantum dots (PQDs), a unique site-controlled family of quantum emitters that have proven to be excellent sources of single and entangled photons. The most striking features of this system, originating from their peculiar fabrication process, include their inherently 3-dimensional nature and their interconnection to a series of nanostructures that are formed alongside them, such as quantum wells and quantum wires. We present structural and chemical data from cross-sectional and plan view samples of both single and stacked PQDs structures. Our findings identify (i) the shape of the dot, being hexagonal and not triangular as previously assumed, (ii) the chemical distribution at the facets and QD area, displaying clear Indium diffusion, and (iii) a near absence of Aluminium (from the AlAs marker) at the bottom of the growth profile. Our results shed light on previously unreported structural and chemical features of PQDs, which is of extreme relevance for further development of this family of quantum emitters