TY - JOUR A1 - Yu, Leo A1 - Natarajan, Chandra M. A1 - Horikiri, Tomoyuki A1 - Langrock, Carsten A1 - Pelc, Jason S. A1 - Tanner, Michael G. A1 - Abe, Eisuke A1 - Maier, Sebastian A1 - Schneider, Christian A1 - Höfling, Sven A1 - Kamp, Martin A1 - Hadfield, Robert H. A1 - Fejer, Martin M. A1 - Yamamoto, Yoshihisa T1 - Two-photon interference at telecom wavelengths for time-bin-encoded single photons from quantum-dot spin qubits JF - Nature Communications N2 - Practical quantum communication between remote quantum memories rely on single photons at telecom wavelengths. Although spin-photon entanglement has been demonstrated in atomic and solid-state qubit systems, the produced single photons at short wavelengths and with polarization encoding are not suitable for long-distance communication, because they suffer from high propagation loss and depolarization in optical fibres. Establishing entanglement between remote quantum nodes would further require the photons generated from separate nodes to be indistinguishable. Here, we report the observation of correlations between a quantum-dot spin and a telecom single photon across a 2-km fibre channel based on time-bin encoding and background-free frequency downconversion. The downconverted photon at telecom wavelengths exhibits two-photon interference with another photon from an independent source, achieving a mean wavepacket overlap of greater than 0.89 despite their original wavelength mismatch (900 and 911 nm). The quantum-networking operations that we demonstrate will enable practical communication between solid-state spin qubits across long distances. KW - atom KW - 1550 nm KW - up-conversion KW - heralded entanglement KW - emission KW - interface KW - generation KW - communication KW - downconversion Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-138677 VL - 6 ER - TY - JOUR A1 - Tempel, Jean-Sebastian A1 - Veit, Tempel A1 - Assmann, Marc A1 - Kreilkamp, Lars Erik A1 - Höfling, Sven A1 - Kamp, Martin A1 - Forchel, Alfred A1 - Bayer, Manfred T1 - Temperature dependence of pulsed polariton lasing in a GaAs microcavity JF - New Journal of Physics N2 - The second-order correlation function g\(^2\)(\(\tau\) = 0), input-output curves and pulse duration of the emission from a microcavity exciton-polariton system subsequent to picosecond-pulsed excitation are measured for different temperatures. At low temperatures a two-threshold behaviour emerges, which has been attributed to the onset of polariton lasing and conventional lasing at the first and the second threshold, respectively. We observe that polariton lasing is stable up to temperatures comparable with the exciton binding energy. At higher temperatures a single threshold displays the direct transition from thermal emission to photon lasing. KW - semiconductor microavity KW - quantized vortices KW - cavity polaritons KW - room temperature KW - excitons KW - time Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-134022 VL - 14 IS - 083014 ER - TY - JOUR A1 - Dyksik, Mateusz A1 - Motyka, Marcin A1 - Sęk, Grzegorz A1 - Misiewicz, Jan A1 - Dallner, Matthias A1 - Weih, Robert A1 - Kamp, Martin A1 - Höfling, Sven T1 - Submonolayer Uniformity of Type II InAs/GaInSb W-shaped Quantum Wells Probed by Full-Wafer Photoluminescence Mapping in the Mid-infrared Spectral Range JF - Nanoscale Research Letters N2 - The spatial uniformity of GaSb- and InAs substrate-based structures containing type II quantum wells was probed by means of large-scale photoluminescence (PL) mapping realized utilizing a Fourier transform infrared spectrometer. The active region was designed and grown in a form of a W-shaped structure with InAs and GaInSb layers for confinement of electrons and holes, respectively. The PL spectra were recorded over the entire 2-in. wafers, and the parameters extracted from each spectrum, such as PL peak energy position, its linewidth and integrated intensity, were collected in a form of two-dimensional spatial maps. Throughout the analysis of these maps, the wafers' homogeneity and precision of the growth procedure were investigated. A very small variation of PL peak energy over the wafer indicates InAs quantum well width fluctuation of only a fraction of a monolayer and hence extraordinary thickness accuracy, a conclusion further supported by high uniformity of both the emission intensity and PL linewidth. KW - interband cascade lasers KW - fourier transform spectroscopy KW - mid-infrared KW - type II quantum wells KW - spatially resolved photoluminescence Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-139733 VL - 10 IS - 402 ER - TY - JOUR A1 - Lee, Eun-Hye A1 - Song, Jin-Dong A1 - Han, Il-Ki A1 - Chang, Soo-Kyung A1 - Langer, Fabian A1 - Höfling, Sven A1 - Forchel, Alfred A1 - Kamp, Martin A1 - Kim, Jong-Su T1 - Structural and optical properties of position-retrievable low-density GaAs droplet epitaxial quantum dots for application to single photon sources with plasmonic optical coupling JF - Nanoscale Research Letters N2 - The position of a single GaAs quantum dot (QD), which is optically active, grown by low-density droplet epitaxy (DE) (approximately 4 QDs/μm\(^{2}\)), was directly observed on the surface of a 45-nm-thick Al\(_{0.3}\)Ga\(_{0.7}\)As capping layer. The thin thickness of AlGaAs capping layer is useful for single photon sources with plasmonic optical coupling. A micro-photoluminescence for GaAs DE QDs has shown exciton/biexciton behavior in the range of 1.654 to 1.657 eV. The direct observation of positions of low-density GaAs DE QDs would be advantageous for mass fabrication of devices that use a single QD, such as single photon sources. KW - quantum dot KW - droplet epitaxy KW - micro-photoluminescence KW - single photon KW - GaAs Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-143692 VL - 10 IS - 114 ER - TY - JOUR A1 - Redlich, Christoph A1 - Lingnau, Benjamin A1 - Holzinger, Steffen A1 - Schlottmann, Elisabeth A1 - Kreinberg, Sören A1 - Schneider, Christian A1 - Kamp, Martin A1 - Höfling, Sven A1 - Wolters, Janik A1 - Reitzenstein, Stephan A1 - Lüdge, Kathy T1 - Mode-switching induced super-thermal bunching in quantum-dot microlasers JF - New Journal of Physics N2 - The super-thermal photon bunching in quantum-dot (QD) micropillar lasers is investigated both experimentally and theoretically via simulations driven by dynamic considerations. Using stochastic multi-mode rate equations we obtain very good agreement between experiment and theory in terms of intensity profiles and intensity-correlation properties of the examined QD micro-laser's emission. Further investigations of the time-dependent emission show that super-thermal photon bunching occurs due to irregular mode-switching events in the bimodal lasers. Our bifurcation analysis reveals that these switchings find their origin in an underlying bistability, such that spontaneous emission noise is able to effectively perturb the two competing modes in a small parameter region. We thus ascribe the observed high photon correlation to dynamical multistabilities rather than quantum mechanical correlations. KW - microlaser KW - nonlinear dynamics KW - correlation properties KW - photon statistics KW - noise and multimode dynamics KW - quantum dot laser Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-166286 VL - 18 IS - 063011 ER - TY - JOUR A1 - Kochereshko, Vladimir P. A1 - Durnev, Mikhail V. A1 - Besombes, Lucien A1 - Mariette, Henri A1 - Sapega, Victor F. A1 - Askitopoulos, Alexis A1 - Savenko, Ivan G. A1 - Liew, Timothy C. H. A1 - Shelykh, Ivan A. A1 - Platonov, Alexey V. A1 - Tsintzos, Simeon I. A1 - Hatzopoulos, Z. A1 - Savvidis, Pavlos G. A1 - Kalevich, Vladimir K. A1 - Afanasiev, Mikhail M. A1 - Lukoshkin, Vladimir A. A1 - Schneider, Christian A1 - Amthor, Matthias A1 - Metzger, Christian A1 - Kamp, Martin A1 - Hoefling, Sven A1 - Lagoudakis, Pavlos A1 - Kavokin, Alexey T1 - Lasing in Bose-Fermi mixtures JF - Scientific Reports N2 - Light amplification by stimulated emission of radiation, well-known for revolutionising photonic science, has been realised primarily in fermionic systems including widely applied diode lasers. The prerequisite for fermionic lasing is the inversion of electronic population, which governs the lasing threshold. More recently, bosonic lasers have also been developed based on Bose-Einstein condensates of exciton-polaritons in semiconductor microcavities. These electrically neutral bosons coexist with charged electrons and holes. In the presence of magnetic fields, the charged particles are bound to their cyclotron orbits, while the neutral exciton-polaritons move freely. We demonstrate how magnetic fields affect dramatically the phase diagram of mixed Bose-Fermi systems, switching between fermionic lasing, incoherent emission and bosonic lasing regimes in planar and pillar microcavities with optical and electrical pumping. We collected and analyzed the data taken on pillar and planar microcavity structures at continuous wave and pulsed optical excitation as well as injecting electrons and holes electronically. Our results evidence the transition from a Bose gas to a Fermi liquid mediated by magnetic fields and light-matter coupling. KW - Bose-Fermi KW - magnetic fields KW - Bose gas KW - Fermi liquid KW - light-matter coupling Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-168152 VL - 6 IS - 20091 ER - TY - JOUR A1 - Motyka, Marcin A1 - Sęk, Grzegorz A1 - Ryczko, Krzysztof A1 - Dyksik, Mateusz A1 - Weih, Robert A1 - Patriarche, Gilles A1 - Misiewicz, Jan A1 - Kamp, Martin A1 - Höfling, Sven T1 - Interface Intermixing in Type II InAs/GaInAsSb Quantum Wells Designed for Active Regions of Mid-Infrared-Emitting Interband Cascade Lasers JF - Nanoscale Research Letters N2 - The effect of interface intermixing in W-design GaSb/AlSb/InAs/Ga\(_{0.665}\)In\(_{0.335}\)As\(_x\)Sb\(_{1-x}\)/InAs/AlSb/GaSb quantum wells (QWs) has been investigated by means of optical spectroscopy supported by structural data and by band structure calculations. The fundamental optical transition has been detected at room temperature through photoluminescence and photoreflectance measurements and appeared to be blueshifted with increasing As content of the GaInAsSb layer, in contrast to the energy-gap-driven shifts calculated for an ideally rectangular QW profile. The arsenic incorporation into the hole-confining layer affects the material and optical structure also altering the InAs/GaInAsSb interfaces and their degree of intermixing. Based on the analysis of cross-sectional transmission electron microscopy images and energy-dispersive X-ray spectroscopy, we could deduce the composition distribution across the QW layers and hence simulate more realistic confinement potential profiles. For such smoothed interfaces that indicate As-enhanced intermixing, the energy level calculations have been able to reproduce the experimentally obtained trend. KW - FTIR spectroscopy KW - type II GaIn(As)Sb/GaSb KW - QW interface profile KW - intermixing KW - interband cascade lasers KW - EDX spectra Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-136386 VL - 10 IS - 471 ER - TY - JOUR A1 - Jahnke, Frank A1 - Gies, Christopher A1 - Aßmann, Marc A1 - Bayer, Manfred A1 - Leymann, H.A.M. A1 - Foerster, Alexander A1 - Wiersig, Jan A1 - Schneider, Christian A1 - Kamp, Martin A1 - Höfling, Sven T1 - Giant photon bunching, superradiant pulse emission and excitation trapping in quantum-dot nanolasers JF - Nature Communications N2 - Light is often characterized only by its classical properties, like intensity or coherence. When looking at its quantum properties, described by photon correlations, new information about the state of the matter generating the radiation can be revealed. In particular the difference between independent and entangled emitters, which is at the heart of quantum mechanics, can be made visible in the photon statistics of the emitted light. The well-studied phenomenon of superradiance occurs when quantum–mechanical correlations between the emitters are present. Notwithstanding, superradiance was previously demonstrated only in terms of classical light properties. Here, we provide the missing link between quantum correlations of the active material and photon correlations in the emitted radiation. We use the superradiance of quantum dots in a cavity-quantum electrodynamics laser to show a direct connection between superradiant pulse emission and distinctive changes in the photon correlation function. This directly demonstrates the importance of quantum–mechanical correlations and their transfer between carriers and photons in novel optoelectronic devices. KW - photon bunching KW - quantum mechanics KW - superradiant pulse emission Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-166144 VL - 7 IS - 11540 ER - TY - JOUR A1 - Rau, Markus A1 - Heindel, Tobias A1 - Unsleber, Sebastian A1 - Braun, Tristan A1 - Fischer, Julian A1 - Frick, Stefan A1 - Nauerth, Sebastian A1 - Schneider, Christian A1 - Vest, Gwenaelle A1 - Reitzenstein, Stephan A1 - Kamp, Martin A1 - Forchel, Alfred A1 - Höfling, Sven A1 - Weinfurter, Harald T1 - Free space quantum key distribution over 500 meters using electrically driven quantum dot single-photon sources-a proof of principle experiment JF - New Journal of Physics N2 - Highly efficient single-photon sources (SPS) can increase the secure key rate of quantum key distribution (QKD) systems compared to conventional attenuated laser systems. Here we report on a free space QKD test using an electrically driven quantum dot single-photon source (QD SPS) that does not require a separate laser setup for optical pumping and thus allows for a simple and compact SPS QKD system. We describe its implementation in our 500 m free space QKD system in downtown Munich. Emulating a BB84 protocol operating at a repetition rate of 125 MHz, we could achieve sifted key rates of 5-17 kHz with error ratios of 6-9% and g((2))(0)-values of 0.39-0.76. KW - QKD KW - electrically driven KW - free space KW - quantum dots KW - quantum key distribution Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-116760 VL - 16 IS - 043003 ER - TY - JOUR A1 - Amthor, Matthias A1 - Weißenseel, Sebastian A1 - Fischer, Julian A1 - Kamp, Martin A1 - Schneider, Christian A1 - Höfling, Sven T1 - Electro-optical switching between polariton and cavity lasing in an InGaAs quantum well microcavity N2 - We report on the condensation of microcavity exciton polaritons under optical excitation in a microcavity with four embedded InGaAs quantum wells. The polariton laser is characterized by a distinct nonlinearity in the input-output-characteristics, which is accompanied by a drop of the emission linewidth indicating temporal coherence and a characteristic persisting emission blueshift with increased particle density. The temporal coherence of the device at threshold is underlined by a characteristic drop of the second order coherence function to a value close to 1. Furthermore an external electric field is used to switch between polariton regime, polariton condensate and photon lasing. KW - Quantum-well, -wire and -dot devices KW - Scattering KW - stimulated KW - Resonators KW - Microcavity devices Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-111130 ER -