Two-photon excitation with finite pulses unlocks pure dephasing-induced degradation of entangled photons emitted by quantum dots

Semiconductor quantum dots have emerged as an especially promising platform for the generation of polarization-entangled photon pairs. However, it was demonstrated recently that the two-photon excitation scheme employed in state-of-the-art experiments limits the achievable degree of entanglement by introducing which-path information. In this work, the combined impact of two-photon excitation and longitudinal acoustic phonons on photon pairs emitted by strongly-confining quantum dots is investigated. It is found that phonons further reduce the achievable degree of entanglement even in the limit of vanishing temperature due to phonon-induced pure dephasing and phonon-assisted one-photon processes, which increase the reexcitation probability. In addition, the degree of entanglement, as measured by the concurrence, decreases with rising temperature and/or pulse duration, even if the excitonic fine-structure splitting is absent and when higher electronic states are out of reach. Furthermore, in the case of finite fine-structure splittings, phonons enlarge the discrepancy in concurrence for different laser polarizations.Comment: 10 pages, 3 figure

Dolls/puppets as soulmates – biographical traces of dolls/puppets in art, literature, work and performance

https://dedo.ub.uni-siegen.deDie vorliegende vierte Ausgabe der Zeitschrift denkste: puppe / just a bit of: doll (de:do), ein multidisziplinäres Online-Journal für Mensch-Puppen-Diskurse, greift den Themenschwerpunkt Puppen als Seelenverwandte – biographische Spuren von Puppen in Kunst, Literatur, Werk und Darstellung auf. Es geht um die Frage nach Wirkungen früher Puppenerfahrungen in der späteren künstlerischen Arbeit und damit nach den möglichen (biographischen) Wurzeln und Zusammenhängen von Puppenmotiv und Puppen-Narrativen im künstlerisch-literarischen Werk. Puppenbezüge in Werk- und Schaffensprozessen können frühe Erfahrungen biographischer Brüche und Verletzungen transformieren bzw. sie künstlerisch produktiv integrieren, sie können aber auch Ausdruck für Kontinuität und Intensivierung früher Prägungen und Vorlieben sein. In den vorliegenden Beiträgen geht es um puppenbezogene künstlerische Ausdrucksformen, die als Beiträge hier formal unterschiedlich aufbereitet werden: als wissenschaftsbasierter Text, Selbstbericht, Miszelle, Rezension, Interview und: Kunstwerk. Untersucht und thematisiert werden Puppen-Sammlungen, die Herstellung besonderer Puppen, literarische Puppentexte, Inszenierungen und Bilder. Außerdem wurden weitere Beiträge einbezogen, die Puppen als Varianten „künstlicher Menschen“ in unterschiedlichsten Themenbezügen behandeln. In vielen Beiträgen deutet sich an, dass die Affinität zum „Phänomen Puppe“ in seinen verschiedenen künstlerischen Umsetzungsformen auf biographisch geprägte Spuren verweist: als Ausdrucks- und Darstellungsmittel steht die Puppe somit auch für etwas Besonderes der Menschen, die sich künstlerisch auf sie beziehen und mit ihr interagieren und „spielen“.This fourth issue of denkste: puppe / just a bit of: doll (de:do), a multidisciplinary online journal for human-doll discourses, takes up the thematic focus on dolls/puppets as soulmates – biographical traces of dolls/puppets in art, literature, work and performance. It is about the impact of early doll experiences in later artistic work and thus about the possible (biographical) roots and connections of doll motifs and doll narratives in artistic-literary work. Doll/puppet references in work and creative processes can transform early experiences of biographical breaks and harm or integrate them in an artistically productive way, but they can also be an expression of continuity and intensification of early experience and preferences. The present contributions deal with doll/puppet-related artistic forms of expression, which are formally presented in different ways: as science-based text, self-report, miscellaneous, review, interview and: work of art. Doll/puppet collections, the making of particular puppets, literary puppet texts, performances and images are examined and addressed. In addition, further contributions were included, which deal with dolls as variants of "artificial humans" in the most diverse thematic contexts. Most of the contributions indicate that the affinity to the “phenomenon of the doll” in its various artistic forms of realization refers to biographically shaped traces: as a means of expression and representation the doll thus also stands for something special about the human beings who refer to it artistically and interact and "play" with it

Magnetophotoluminescence study of excitons confined in GaAs quantum dots

In the field of quantum information technology, single photons are a crucial resource for realizing qubits. An advantage of a photon based qubit compared to other systems is its low interaction with the environment. This allows a decoherence free distribution of quantum states over large distances at the speed of light. Therefore, a lot of effort is put in the research of single photon-sources. Among the different systems under investigation, semiconductor quantum dots are promising candidates to act as an on-demand single photon source in advanced quantum technology applications. While photons are the ideal candidates for quantum information transport, the situation is different when it comes to quantum information storage and processing. Therefore, a transfer from one physical form to another is needed to enable quantum networks and quantum entanglement over long distances. For this purpose, electron spin states confined in quantum dots of a direct bandgap semiconductor are preferred and the conversion of photon qubits into spin qubits is necessary. However, in order to perform a conversion between photonic and spin qubits, elaborate knowledge of the response of excited states in a quantum dot to an external magnetic field is required. This response is specified by the g-factor and the diamagnetic coefficient. In this thesis magnetic field dependent photoluminescence measurements are performed to study the g-factors of different complexes as well as the diamagnetic shift of optical transitions of an optically excited gallium-arsenide (GaAs) quantum dot. There have already been researches about magneto-optical properties of quantum dots, especially for indium-gallium-arsenide (InGaAs) systems. However, similar works for droplet-etched GaAs quantum dots are still missing. While for strongly confining systems, e.g. InGaAs quantum dots the single-particle Hamiltonian is used to extract the magnetic properties, the question arises if this description is also valid for weak confinement systems like our GaAs quantum dots. This work proves that an evaluation with the single-particle picture is not reasonable. Nevertheless, by investigating the magnetic properties, the various transitions in a QD are studied and assigned to certain charge complexes.submitted by Barbara Ursula Lehner, BScUniversität Linz, Masterarbeit, 2019(VLID)459085