Impact of ex-situ rapid thermal annealing on the magneto-optical properties and the oscillator strength of In(Ga)As quantum dots

The authors acknowledge financial support by the State of Bavaria and the German Ministry of Education and Research (BMBF) within the project Q.com-HL.We discuss the influence of a rapid thermal annealing step on the magneto-optical emission properties of In(Ga)As/GaAs quantum dots. We map out a strong influence of the growth- and anneling parameters on the quantum excitons' effective Land\'e g-factors and in particular on their diamagnetic coefficients, which we directly correlate with the modification of the emitters shape and material composition. In addition, we study the excitons' spontaneous emission lifetime as a function of the annealing temperature and the dot height, and observe a strong increase of the emission rate with the quantum dot volume. The corresponding increase in oscillator strenth yields fully consistent results with the analysis of the diamagenic behavior. In particular, we demonstrate that a rapid thermal annealing step of 850ºC can be employed to increase the oscillator strength of as-grown InAs/GaAs QDs by more than a factor of 2.PostprintPeer reviewe

Spatio-temporal coherence in vertically emitting GaAs-based electrically driven polariton lasers

Authors gratefully acknowledge the financial support by the state of Bavaria, the DFG within the projects Schn1376-3.1 as well as KL3124/2-1 and the Wurzburg-Dresden Cluster of Excellence on Complexity and Topology in Quantum Matter - ct.qmat. S.H. is grateful for funding received within the EPSRC Hybrid Polaritonics programme grant (EP/M025330/1).We report on the implementation of a GaAs-based, vertically emitting electrically pumped polariton laser operated at cryogenic temperatures. The structure consists of a high quality factor AlGaAs/AlAs microcavity (Q=15 000) with two stacks of four GaAs quantum wells and features a Rabi splitting of 11 meV. Polariton lasing manifests by a clear threshold in the input–output characteristics of our device with a sharp drop in the emission linewidth and a continuous blueshift of 0.7 meV above threshold with increasing injection current. We measure spatial and temporal coherence of our device in the condensed phase by utilizing interference spectroscopy. Our results clearly demonstrate that electrically driven polariton lasers have promise as monolithic polaritonic sources of coherent light.PostprintPeer reviewe

Room temperature organic exciton-polariton condensate in a lattice

Funding: The Würzburg group acknowledges financial support from the state of Bavaria. We also thank the Würzburg–Dresden Cluster of Excellence ct.qmat for financial support.Interacting Bosons in artificial lattices have emerged as a modern platform to explore collective manybody phenomena and exotic phases of matter as well as to enable advanced on-chip simulators. On chip, exciton–polaritons emerged as a promising system to implement and study bosonic non-linear systems in lattices, demanding cryogenic temperatures. We discuss an experiment conducted on a polaritonic lattice at ambient conditions: We utilize fluorescent proteins providing ultra-stable Frenkel excitons. Their soft nature allows for mechanically shaping them in the photonic lattice. We demonstrate controlled loading of the coherent condensate in distinct orbital lattice modes of different symmetries. Finally, we explore the self-localization of the condensate in a gap-state, driven by the interplay of effective interaction and negative effective mass in our lattice. We believe that this work establishes organic polaritons as a serious contender to the well-established GaAs platform for a wide range of applications relying on coherent Bosons in lattices.Publisher PDFPeer reviewe

Observation of macroscopic valley-polarized monolayer exciton-polaritons at room temperature

Funding: the State of Bavaria and the ERC (unlimit-2D), the DFG via SFB689, GRK 1570 and KO3612/1-1.In this Rapid Communication, we address the chiral properties of valley exciton-polaritons in a monolayer of WS2 in the regime of strong light-matter coupling with a Tamm-plasmon resonance. We observe that the effect of valley polarization, which manifests in the circular polarization of the emitted photoluminescence as the sample is driven by a circularly polarized laser, is strongly enhanced in comparison to bare WS2 monolayers and can even be observed under strongly nonresonant excitation at ambient conditions. In order to explain this effect in more detail, we study the relaxation and decay dynamics of exciton-polaritons in our device, elaborate the role of the dark state, and present a microscopic model to explain the wave-vector-dependent valley depolarization by the linear polarization splitting inherent to the microcavity. We believe that our findings are crucial for designing novel polariton-valleytronic devices which can be operated at room temperature.PostprintPeer reviewe

Intrinsic and environmental effects on the interference properties of a high-performance quantum dot single-photon source

We acknowledge support by the State of Bavaria and the German Ministry of Education and Research (BMBF) within the project Q.com. J.I.-S. and J.M. acknowledge support from the Danish Research Council (DFF-4181-00416) and Villum Fonden (NATEC Centre). This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 703193.We report a joint experimental and theoretical study of the interference properties of a single-photon source based on a In(Ga)As quantum dot embedded in a quasiplanar GaAs microcavity. Using resonant laser excitation with a pulse separation of 2 ns, we find near-perfect interference of the emitted photons, and a corresponding indistinguishability of I=(99.6^+0.4_−1.4)%. For larger pulse separations, quasiresonant excitation conditions, increasing pump power, or with increasing temperature, the interference contrast is progressively and notably reduced. We present a systematic study of the relevant dephasing mechanisms and explain our results in the framework of a microscopic model of our system. For strictly resonant excitation, we show that photon indistinguishability is independent of pump power, but strongly influenced by virtual phonon-assisted processes which are not evident in excitonic Rabi oscillations.Publisher PDFPeer reviewe

Room temperature strong coupling in a semiconductor microcavity with embedded AlGaAs quantum wells designed for polariton lasing

This work was supported by the State of Bavaria.We report a systematic study of the temperature and excitation density behavior of an AlAs/AlGaAs, vertically emitting microcavity with embedded ternary Al0.20Ga0.80As/AlAs quantum wells in the strong coupling regime. Temperature-dependent photoluminescence measurements of the bare quantum wells indicate a crossover from the type-II indirect to the type-I direct transition. The resulting mixing of quantum well and barrier ground states in the conduction band leads to an estimated exciton binding energy systematically exceeding 25 meV. The formation of exciton-polaritons is evidenced in our quantum well microcavity via reflection measurements with Rabi splittings ranging from (13.93 ± 0.15) meV at low temperature (30 K) to (8.58 ± 0.40) meV at room temperature (300 K). Furthermore, the feasibility of polariton laser operation is demonstrated under non-resonant optical excitation conditions at 20 K and emission around 1.835 eV.PostprintPeer reviewe

Understanding the management of osteoarthritis in Australia: a qualitative study of GPs and orthopaedic surgeons in Tasmania, Australia

ObjectiveUsing a qualitative design this study aimed to 1) explore the attitudes towards and understanding of osteoarthritis (OA) held by Tasmanian general practitioners (GPs) and orthopaedic surgeons, 2) gain a deeper understanding of conservative and surgical management and 3) identify key barriers and challenges.DesignPurposive sampling was used to recruit 17 ​GPs and 10 surgeons from Tasmania, Australia. Semi-structured interviews were audio-recorded, transcribed, coded, and thematically analysed to document understanding of OA, management and treatment decision making.ResultsGPs and surgeons had a shared understanding of the cause and management of OA which aligned well with evidence-based best practice. Most GPs acknowledged that severity of disease on an X-Ray does not correlate well with symptoms, although some GPs reported always using imaging to support their diagnosis. Conservative management was highly supported by all interviewees, focussing on exercise and/or physiotherapy. Key treatment barriers included managing poor patient understanding of OA, unrealistic expectations for treatment, lack of patient motivation and scepticism towards exercise, and cost and accessibility of conservative treatment options. Surgery was considered a suitable option when conservative management options had been exhausted.ConclusionThis study uniquely interviewed GPs and surgeons from the same population, capturing two crucial areas of OA management. Some key barriers to treatment were identified and options for improving treatment include creating opportunities for increased patient education about OA, enhanced accessibility to OA conservative management programs along with improved reimbursement models supporting conservative management as first-line OA treatment

Nonresonant spin selection methods and polarization control in exciton-polariton condensates

The authors would like to thank the State of Bavaria and the german research association (DFG) within the DFG project Schn1376 3-1 for financial support. E.A.O. acknowledges support by the Australian Research Council (ARC). A.N. acknowledges support from Icelandic Research Fund, Grant No. 196301-051 and from Russian Science Foundation, Grant No. 18-72-10110. T.H.H. gratefully acknowledges support by the Elite Network Bavaria within the doctoral training programme “Topological Insulators” (Tols 836315). Sample growth by S. Brodbeck, and technology support by M. Emmerling and A. Wolf is acknowledged. C. S. acknowledges discussions with T. Kiessling. T.C.H.L. was supported by the Singapore Ministry of Education Academic Research Fund Tier 2, Project No. MOE2017-T2-1-001.Bosonic condensates of exciton-polaritons are characterized by a well-defined pseudospin, which makes them attractive for quantum information schemes and spintronic applications, as well as the exploration of synthetic spin-orbit coupling. However, precise polarization control of coherent polariton condensates under nonresonant injection, the most important ingredient for such advanced studies, still remains a core challenge. Here, we address this problem and demonstrate unprecedented control of the pseudospin of an exciton-polariton condensate. The ultrafast stimulated scattering process allows the observation of completely spin-polarized condensates under highly nonresonant, circularly polarized excitation. This conservation of spin population translates, in the case of linearly polarized excitation, into an elliptically polarized emission. The degree of ellipticity can be controlled by varying the exciton-photon detuning and condensate density. Additionally, cavity engineering allows us to generate completely linearly polarized condensates with a deterministically chosen orientation. Our findings are of fundamental importance for the engineering and design of polaritonic devices that harness the spinor degree of freedom, such as chiral lasers, spin switches, and polaritonic topological insulator circuits.PostprintPeer reviewe