Orwell Court. Gegen/Blicke in einer betongewordenen Wohnutopie im Londoner Nordosten

Die Fotoserie und der Begleittext untersuchen Blicke und Gegenblicke innerhalb des im Londoner Stadtteil Hackney gelegenen Wohnkomplexes „Orwell Court“, der von Videoüberwachung, Zäunen und Warnschildern dominiert wird. Assoziationen zu dessen Namen, der auf den Autoren des dystopischen Romans 1984 verweist, dienen als Referenz für die Betrachtung des speziellen Raumgefühls des „Orwell Court“, der (Sicherheits)Architektur, sowie deren Individualisierung und Subversion

Operating single quantum emitters with a compact Stirling cryocooler

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Review of Scientific Instruments 86, 013113 (2015) and may be found at https://doi.org/10.1063/1.4906548.The development of an easy-to-operate light source emitting single photons has become a major driving force in the emerging field of quantum information technology. Here, we report on the application of a compact and user-friendly Stirling cryocooler in the field of nanophotonics. The Stirling cryocooler is used to operate a single quantum emitter constituted of a semiconductor quantum dot (QD) at a base temperature below 30 K. Proper vibration decoupling of the cryocooler and its surrounding enables free-space micro-photoluminescence spectroscopy to identify and analyze different charge-carrier states within a single quantum dot. As an exemplary application in quantum optics, we perform a Hanbury-Brown and Twiss experiment demonstrating a strong suppression of multi-photon emission events with g(2)(0) < 0.04 from this Stirling-cooled single quantum emitter under continuous wave excitation. Comparative experiments performed on the same quantum dot in a liquid helium (LHe)-flow cryostat show almost identical values of g(2)(0) for both configurations at a given temperature. The results of this proof of principle experiment demonstrate that low-vibration Stirling cryocoolers that have so far been considered exotic to the field of nanophotonics are an attractive alternative to expensive closed-cycle cryostats or LHe-flow cryostats, which could pave the way for the development of high-quality table-top non-classical light sources.BMBF, 03V0630, Entwicklung einer Halbleiterbasierten Einzelphotonenquelle für die Quanteninformationstechnologie (QSOURCE)DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement

Advanced in-situ electron-beam lithography for deterministic nanophotonic device processing

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Review of Scientific Instruments 86, 073903 (2015) and may be found at https://doi.org/10.1063/1.4926995.We report on an advanced in-situ electron-beam lithography technique based on high-resolution cathodoluminescence (CL) spectroscopy at low temperatures. The technique has been developed for the deterministic fabrication and quantitative evaluation of nanophotonic structures. It is of particular interest for the realization and optimization of non-classical light sources which require the pre-selection of single quantum dots (QDs) with very specific emission features. The two-step electron-beam lithography process comprises (a) the detailed optical study and selection of target QDs by means of CL-spectroscopy and (b) the precise retrieval of the locations and integration of target QDs into lithographically defined nanostructures. Our technology platform allows for a detailed pre-process determination of important optical and quantum optical properties of the QDs, such as the emission energies of excitonic complexes, the excitonic fine-structure splitting, the carrier dynamics, and the quantum nature of emission. In addition, it enables a direct and precise comparison of the optical properties of a single QD before and after integration which is very beneficial for the quantitative evaluation of cavity-enhanced quantum devices.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement

Two-photon interference from remote deterministic quantum dot microlenses

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 110, 011104 (2017) and may be found at https://doi.org/10.1063/1.4973504.We report on two-photon interference (TPI) experiments using remote deterministic single-photon sources. Employing 3D in-situ electron-beam lithography, we fabricate quantum-light sources at specific target wavelengths by integrating pre-selected semiconductor quantum dots within monolithic microlenses. The individual single-photon sources show TPI visibilities of 49% and 22%, respectively, under pulsed p-shell excitation at 80 MHz. For the mutual TPI of the remote sources, we observe an uncorrected visibility of 29%, in quantitative agreement with the pure dephasing of the individual sources. Due to its efficient photon extraction within a broad spectral range (>20 nm), our microlens-based approach is predestinated for future entanglement swapping experiments utilizing entangled photon pairs emitted by distant biexciton-exciton radiative cascades.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, BauelementeEC/FP7/615613/EU/External Quantum Control of Photonic Semiconductor Nanostructures/EXQUISIT

Generation of maximally entangled states and coherent control in quantum dot microlenses

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 112, 153107 (2018) and may be found at https://doi.org/10.1063/1.5020242.The integration of entangled photon emitters in nanophotonic structures designed for the broadband enhancement of photon extraction is a major challenge for quantum information technologies. We study the potential of quantum dot (QD) microlenses as efficient emitters of maximally entangled photons. For this purpose, we perform quantum tomography measurements on InGaAs QDs integrated deterministically into microlenses. Even though the studied QDs show non-zero excitonic fine-structure splitting (FSS), polarization entanglement can be prepared with a fidelity close to unity. The quality of the measured entanglement is only dependent on the temporal resolution of the applied single-photon detectors compared to the period of the excitonic phase precession imposed by the FSS. Interestingly, entanglement is kept along the full excitonic wave-packet and is not affected by decoherence. Furthermore, coherent control of the upper biexcitonic state is demonstrated.DFG, SFB 787, Halbleiter - Nanophotonik: Materialien, Modelle, BauelementeBMBF, 03V0630TIB, Entwicklung einer Halbleiterbasierten Einzelphotonenquelle für die Quanteninformationstechnologi

Projections of Global Emissions of Fluorinated Greenhouse Gases in 2050

This is the result of a German study which underlines once more the urgent need for measures to reduce F-gas emissions. Global emissions of fluorinated greenhouse gases (F-gases) will increase to 4 gigatonnes of CO2 equivalents by 2050 if no political mitigation measures are taken. The contribution of F-gases to global warming is projected to grow from 1.3% (2004) to 7.9% of total direct CO2 emissions

Single-photon emission at a rate of 143 MHz from a deterministic quantum-dot microlens triggered by a mode-locked vertical-external-cavity surface-emitting laser

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 107, 041105 (2015) and may be found at https://doi.org/10.1063/1.4927429.We report on the realization of a quantum dot (QD) based single-photon source with a record-high single-photon emission rate. The quantum light source consists of an InGaAs QD which is deterministically integrated within a monolithic microlens with a distributed Bragg reflector as back-side mirror, which is triggered using the frequency-doubled emission of a mode-locked vertical-external-cavity surface-emitting laser (ML-VECSEL). The utilized compact and stable laser system allows us to excite the single-QD microlens at a wavelength of 508 nm with a pulse repetition rate close to 500 MHz at a pulse width of 4.2 ps. Probing the photon statistics of the emission from a single QD state at saturation, we demonstrate single-photon emission of the QD-microlens chip with g(2)(0) < 0.03 at a record-high single-photon flux of (143 ± 16) MHz collected by the first lens of the detection system. Our approach is fully compatible with resonant excitation schemes using wavelength tunable ML-VECSELs, which will optimize the quantum optical properties of the single-photon emission in terms of photon indistinguishability.BMBF, 03V0630, Entwicklung einer Halbleiterbasierten Einzelphotonenquelle für die Quanteninformationstechnologie (QSOURCE)DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, BauelementeDFG, 192635911, GRK 1782: Funktionalisierung von HalbleiternDFG, 223848855, SFB 1083: Struktur und Dynamik innerer Grenzfläche

In-situ electron-beam lithography of deterministic single-quantum-dot mesa-structures using low-temperature cathodoluminescence spectroscopy

We report on the deterministic fabrication of sub-um mesa structures containing single quantum dots by in-situ electron-beam lithography. The fabrication method is based on a two-step lithography process using a low-temperature cathodoluminescence (CL) spectroscopy setup. In the first step the position and spectral features of single InGaAs quantum dots (QDs) are detected by CL. Then circular sub-um mesa-structures are exactly defined by high-resolution electron-beam lithography and subsequent etching in the second step. CL spectroscopy and micro-photoluminscence spectroscopy demonstrate the high optical quality of the single-QD mesa-structures with emission linewidths below 15 ueV and g(2)(0) = 0.04. Our lithography method allows for an alignment precision better than 100 nm which paves the way for a fully-deterministic device technology using in-situ CL lithography.Comment: 4 pages, 4 figure

Energy-time entanglement from a resonantly driven quantum dot three-level system

Entanglement is a major resource in advanced quantum technology, where it can enable secure exchange of information over large distances. Energy-time entanglement is particularly attractive for its beneficial robustness in fiber-based quantum communication and can be demonstrated in the Franson interferometer. We report on Franson-type interference from a resonantly driven biexciton cascade under continuous wave excitation. Our measurements yield a maximum visibility of (73 $\pm$ 2)% surpassing the limit of violation of Bell's inequality (70.7%) by more than one standard deviation. Despite being unable to satisfy a loophole free violation, our work demonstrates promising results concerning future works on such a system. Furthermore, our systematical studies on the impact of driving strength indicate that dephasing mechanisms and deviations from the cascaded emission have major impact on the degree of the measured energy-time entanglement