Valley Bosonic Stimulation of Exciton-Polaritons in a Monolayer Semiconductor

The newly discovered valley degree of freedom (DOF) in atomically thin two-dimensional (2D) transition metal dichalcogenides (TMDs) offers a promising platform to explore rich nonlinear physics, such as spinor Bose-Einstein condensate (BEC) and novel valleytronics applications. However, the critical nonlinear effect, such as valley polariton bosonic stimulation (BS), has long remained an unresolved challenge due to the generation of limited polariton ground state densities necessary to induce the stimulated scattering of polaritons in specific valleys. Here, we report, for the first time, the valley bosonic stimulation of exciton-polaritons via spin-valley locking in a WS2 monolayer microcavity. This is achieved by the resonant injection of valley polaritons at specific energy and wavevector, which allows spin-polarized polaritons to efficiently populate their ground state and induce a valley-dependent bosonic stimulation. As a result, we observe the nonlinear self-amplification of polariton emission from the valley-dependent ground state. Our finding paves the way for both fundamental study of valley polariton BEC physics and non-linear optoelectronic devices such as spin-dependent parametric oscillators and spin-lasers.Comment: Article + Supplementary Information (tot. 21 pages

Realizing the classical XY Hamiltonian in polariton simulators.

The vast majority of real-life optimization problems with a large number of degrees of freedom are intractable by classical computers, since their complexity grows exponentially fast with the number of variables. Many of these problems can be mapped into classical spin models, such as the Ising, the XY or the Heisenberg models, so that optimization problems are reduced to finding the global minimum of spin models. Here, we propose and investigate the potential of polariton graphs as an efficient analogue simulator for finding the global minimum of the XY model. By imprinting polariton condensate lattices of bespoke geometries we show that we can engineer various coupling strengths between the lattice sites and read out the result of the global minimization through the relative phases. Besides solving optimization problems, polariton graphs can simulate a large variety of systems undergoing the U(1) symmetry-breaking transition. We realize various magnetic phases, such as ferromagnetic, anti-ferromagnetic, and frustrated spin configurations on a linear chain, the unit cells of square and triangular lattices, a disordered graph, and demonstrate the potential for size scalability on an extended square lattice of 45 coherently coupled polariton condensates. Our results provide a route to study unconventional superfluids, spin liquids, Berezinskii-Kosterlitz-Thouless phase transition, and classical magnetism, among the many systems that are described by the XY Hamiltonian

Non-resonant optical control of a spinor polariton condensate

We investigate the spin dynamics of polariton condensates spatially separated from and effectively confined by the pumping exciton reservoir. We obtain a strong correlation between the ellipticity of the non-resonant optical pump and the degree of circular polarisation (DCP) of the condensate at the onset of condensation. With increasing excitation density we observe a reversal of the DCP. The spin dynamics of the trapped condensate are described within the framework of the spinor complex Ginzburg-Landau equations in the Josephson regime, where the dynamics of the system are reduced to a current-driven Josephson junction. We show that the observed spin reversal is due to the interplay between an internal Josephson coupling effect and the detuning of the two projections of the spinor condensate via transition from a synchronised to a desynchronised regime. These results suggest that spinor polariton condensates can be controlled by tuning the non-resonant excitation density offering applications in electrically pumped polariton spin switches

Half-skyrmion spin textures in polariton microcavities

We study the polarization dynamics of a spatially expanding polariton condensate under nonresonant linearly polarized optical excitation. The spatially and temporally resolved polariton emission reveals the formation of non-trivial spin textures in the form of a quadruplet polarization pattern both in the linear and circular Stokes parameters, and an octuplet in the diagonal Stokes parameter. The continuous rotation of the polariton pseudospin vector through the condensate due to TE-TM splitting exhibits an ordered pattern of half-skyrmions associated with a half-integer topological number. A theoretical model based on a driven-dissipative Gross-Pitaevskii equation coupled with an exciton reservoir describes the dynamics of the nontrivial spin textures through the optical spin-Hall effect

Half-skyrmion spin textures in polariton microcavities

We study the polarization dynamics of a spatially expanding polariton condensate under nonresonant linearly polarized optical excitation. The spatially and temporally resolved polariton emission reveals the formation of non-trivial spin textures in the form of a quadruplet polarization pattern both in the linear and circular Stokes parameters, and an octuplet in the diagonal Stokes parameter. The continuous rotation of the polariton pseudospin vector through the condensate due to TE-TM splitting exhibits an ordered pattern of half-skyrmions associated with a half-integer topological number. A theoretical model based on a driven-dissipative Gross-Pitaevskii equation coupled with an exciton reservoir describes the dynamics of the nontrivial spin textures through the optical spin-Hall effect

Quantum communication networks with defects in silicon carbide

Quantum communication promises unprecedented communication capabilities enabled by the transmission of quantum states of light. However, current implementations face severe limitations in communication distance due to photon loss. Silicon carbide (SiC) defects have emerged as a promising quantum device platform, offering strong optical transitions, long spin coherence lifetimes and the opportunity for integration with semiconductor devices. Some defects with optical transitions in the telecom range have been identified, allowing to interface with fiber networks without the need for wavelength conversion. These unique properties make SiC an attractive platform for the implementation of quantum nodes for quantum communication networks. We provide an overview of the most prominent defects in SiC and their implementation in spin-photon interfaces. Furthermore, we model a memory-enhanced quantum communication protocol in order to extract the parameters required to surpass a direct point-to-point link performance. Based on these insights, we summarize the key steps required towards the deployment of SiC devices in large-scale quantum communication networks.Comment: 20 pages, 8 figure

Studies of fluidics, linear and nonlinear phenomena in polariton microcavities

Exciton-polaritons are half-light half-matter bosonic quasiparticles formed by the strong coupling between quantum well excitons and the photonic mode of a planar semiconductor microcavity. By increasing the polariton population above a threshold density, polaritons can macroscopically occupy the ground state of the dispersion and form a non-equilibrium Bose-Einstein condensate.This thesis addresses some of the fundamental concepts studied in polariton microcavities, such as dark solitons, polariton spin textures and condensation, by concentrating on the linear and nonlinear nature of these effects.In the first part, the formation of dark solitons is studied by investigating the propagation and scattering of polaritons in a planar microcavity in the linear regime. The propagation of the polariton wave across an extended defect creates phase and intensity patterns with identical qualitative features previously attributed to dark and half-dark solitons of polaritons. By combining both experimental evidence and theoretical analysis, all the experimental observations supporting the formation of dark solitons in polariton microcavities are questioned. Since they are observed with negligible nonlinearity (i.e., polariton-polariton interaction), they are not sufficient to identify dark and half-dark solitons. A condition based on the healing length of the condensate is proposed as a new criterion to identify dark solitons in polariton microcavities.In the second part, the spin dynamics of polariton condensates is investigated in the non-linear emission regime, by studying the spatial, angular, energy and transient dynamics of the polariton emission. In a radially expanding condensate, polaritons with opposite spin arrange themselves in geometrically ordered spin textures and propagate over hundreds of microns in the plane of the microcavity. Depending on the polarization of the excitation pump different spin textures are observed. Moreover, a polariton \spin whirl" namely a spin texture that rotates in the plane of the microcavity on picosecond scale is reported for the first time.Finally, the condensation of polaritons in a strain compensated microcavity is investigated. Signatures of polariton condensation, according to the current understanding of polariton condensates, are experimentally observed, including the observation of a second threshold which marks the transition from the strong to the weak-coupling regime.<br/

Self-Induced Valley Bosonic Stimulation of Exciton Polaritons in a Monolayer Semiconductor

The newly discovered valley degree of freedom in atomically thin two-dimensional transition metal dichalcogenides offers a promising platform to explore rich nonlinear physics, such as spinor Bose-Einstein condensate and novel valleytronics applications. However, the critical nonlinear effect, such as valley polariton bosonic stimulation, has long remained an unresolved challenge due to the generation of limited polariton ground state densities necessary to induce the stimulated scattering of polaritons in specific valleys. Here, we report the self-induced valley bosonic stimulation of exciton polaritons via spin-valley locking in a WS2 monolayer microcavity. This is achieved by the resonant injection of valley polaritons at specific energy and wave vector, which allows spin-polarized polaritons to efficiently populate their ground state and induce a valley-dependent bosonic stimulation. As a result, we observe the nonlinear self-amplification of polariton emission from the valley-dependent ground state. Our finding paves the way for the investigation of spin ordering and phase transitions in transition metal dichalcogenides polariton Bose-Einstein condensate, offering a promising route for the realization of polariton spin lattices in moiré polariton systems and spin lasers.</p

Dataset for Realizing the classical XY Hamiltonian in polariton simulators

Dataset in support to &#39;Realising the classical XY Hamiltonian in polariton simulators&#39; accepted in Nature Materials.</span

Waelder und Forstwirtschaft Deutschlands im globalen Wandel: Strategie fuer eine integrierte Wirkungsanalyse und Bewertung. Teilprojekt 4: Genetische Anpassungsfaehigkeit der wichtigsten Waldbaumarten in Deutschland Abschlussbericht

Aim of part 4 of the project is, to widen the knowledge on adaptedness and adaptability of populations of European Norway spruce and beech under changing climate conditions. The project aimed at 4 topics: Data from the international Norway spruce IUFRO provenance experiment of 1964/68 were compiled and supplied to integrate the individual genetic variation into the yield model and the succession model of the comprehensive project. To widen the knowledge on adaptedness of tree populations to specific climatic conditions information from provenance trials with Norway spruce and beech were analysed. A provenance experiment with beech established in the field and in a greenhouse shows that flushing starts earlier in the greenhouse and takes a longer period of time. Within and among the provenances great variation occurs. If a warming is expected the risk of late frost damages might increase. In an other greenhouse experiment with beech the influence of elevated CO_2-on growth of various provenances was tested. In relation to the predicted warming provenances of Norway spruce of international provenance trials generally show a wide range with regard to survival and diameter growth on the test sites. A few provenances are well adapted to all sites, whereas most of them perform well only under specific site conditions. Simulation studies were run to estimate possible effects on an increasing annual mean temperature and a decreasing annual mean precipitation on the genetic structure based on inventories of isozyme gene loci in provenance trials of Norway spruce in relation to the predicted global warming. Therefore, growth was simulated with the simulation model for growth (Part 3) for several environments. For the simulated final stands mean values of population genetic measures were computed and compared. The simulation model ECO-GENE was further developed to analyse population genetic interactions. The simulation program and the manual are available on the web. (orig.)Ziel des Teilprojekts ist es, Aussagen ueber Angepasstheit und Anpassungsfaehigkeit von europaeischen Fichten- und Buchenpopulationen hinsichtlich der prognostizierten Klimaaenderungen zu treffen. Folgende 4 Teilziele wurden bearbeitet: - Zur Integration der genetisch determinierten individuellen Variation in die Wachstums- und Sukzessionsmodelle des Verbundprojekts wurden Daten aus dem Internationalen IUFRO Provenienzversuch von 1964/68 mit Fichte fuer Sensitivitaetsuntersuchngen im Zuge von Simulationen der natuerlichen Waldentwicklung (Teilprojekt 2) und fuer die Differenzierung von Wachstumskurven nach Provenienzen (Teilprojekt 3) bereitgestellt. - Zur Verbesserung der Kenntnisse ueber die Angepassthteit der Baumpopulationen an bestimmte klimatische Bedingungen wurden Daten aus internationalen Buchen- und Fichten-Provenienzversuchen des Instituts ausgewertet. Ein Buchen-Provenienzversuch mit 2 Klimavarianten (Gewaechshaus/Freiland) ergab einen frueheren und sich ueber einen laengeren Zeitraum hinziehenden Austrieb bei der 'waermeren' Versuchsvariante. Dies laesst eine Spaetfrostgefaehrdung bei Erwaermung erwarten und zwar je nach Provenienz unterschiedlich. In einem weiteren Gewaechshausversuch mit Buche wurde die Reaktion von verschiedenen Provenienzen auf erhoehte atmosphaerische CO_2-Konzentration untersucht. Die Ergebnisse aus den internationalen Fichten-Provenienzversuchen zeigen, dass es bei einer Kontinentalisierung des Klimas zwischen den Herkuenften Unterschiede im Wachstum und in den Ueberlebensraten an einem Standort gibt. Die Provenienzen zeigen eine unterschiedliche Anpassungsfaehigkeit, einige sind an alle Versuchsorten angepasst, waehrend andere nur unter speziellen Standortbedingungen gut gedeihen. - Fuer die Abschaetzung der moeglichen Genverarmung und damit der Reduzierung von adaptiven genetischen Potentialen bei den zu erwartenden Verschiebungen der Vegetationszonen wurde ein Verfahren entwickelt, bei dem das Wachstum eines Bestandes mit bekannter genetischer Struktur unter unterschiedlichen Standortbedingungen mit dem Waldwachstumssimulator SILVA 2.2 (Teilprojekt 3) simuliert wird. Fuer die am Ende der Simulationslaeufe jeweils vorhandenen Baeume werden populationsgenetische Masse fuer Isoenzym-Genmarker mit dem Macro-Paket MacGen berechnet. - Zur Einschaetzung und Charakterisierung der evolutionaeren Anpassungsfaehigkeit der Baumpopulationen wurde das populationsgenetischen Simulationsmodells OeKOe-GEN fertiggestellt. Es ist mit einem Benutzerhandbuch und Beispielsdatensaetzen im Internet verfuegbar. (orig.)SIGLEAvailable from TIB Hannover: F02B1194 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung und Forschung, Berlin (Germany)DEGerman