TY - JOUR A1 - Nitsche, Wolfgang H. A1 - Kim, Na Young A1 - Roumpos, Georgios A1 - Schneider, Christian A1 - Höfling, Sven A1 - Forchel, Alfred A1 - Yamamoto, Yoshihisa T1 - Spatial correlation of two-dimensional bosonic multimode condensates JF - Physical Review A N2 - The Berezinskii-Kosterlitz-Thouless (BKT) theorem predicts that two-dimensional bosonic condensates exhibit quasi-long-range order which is characterized by a slow decay of the spatial coherence. However previous measurements on exciton-polariton condensates revealed that their spatial coherence can decay faster than allowed under the BKT theory, and different theoretical explanations have already been proposed. Through theoretical and experimental study of exciton-polariton condensates, we show that the fast decay of the coherence can be explained through the simultaneous presence of multiple modes in the condensate. KW - Exciton-polariton condensate KW - Long-range order KW - Microcavity KW - Vortices KW - Systems Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-188897 VL - 93 IS - 5 ER - TY - JOUR A1 - Lundt, Nils A1 - Klembt, Sebastian A1 - Cherotchenko, Evgeniia A1 - Betzold, Simon A1 - Iff, Oliver A1 - Nalitov, Anton V. A1 - Klaas, Martin A1 - Dietrich, Christof P. A1 - Kavokin, Alexey V. A1 - Höfling, Sven A1 - Schneider, Christian T1 - Room-temperature Tamm-plasmon exciton-polaritons with a WSe\(_{2}\) monolayer JF - Nature Communications N2 - Solid-state cavity quantum electrodynamics is a rapidly advancing field, which explores the frontiers of light–matter coupling. Metal-based approaches are of particular interest in this field, as they carry the potential to squeeze optical modes to spaces significantly below the diffraction limit. Transition metal dichalcogenides are ideally suited as the active material in cavity quantum electrodynamics, as they interact strongly with light at the ultimate monolayer limit. Here, we implement a Tamm-plasmon-polariton structure and study the coupling to a monolayer of WSe\(_{2}\), hosting highly stable excitons. Exciton-polariton formation at room temperature is manifested in the characteristic energy–momentum dispersion relation studied in photoluminescence, featuring an anti-crossing between the exciton and photon modes with a Rabi-splitting of 23.5 meV. Creating polaritonic quasiparticles in monolithic, compact architectures with atomic monolayers under ambient conditions is a crucial step towards the exploration of nonlinearities, macroscopic coherence and advanced spinor physics with novel, low-mass bosons. KW - optics and photonics KW - two-dimensional materials KW - electronic properties and materials Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-169470 VL - 7 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 - He, Yu-Ming A1 - Iff, Oliver A1 - Lundt, Nils A1 - Baumann, Vasilij A1 - Davanco, Marcelo A1 - Srinivasan, Kartik A1 - Höfling, Sven A1 - Schneider, Christian T1 - Cascaded emission of single photons from the biexciton in monolayered WSe\(_{2}\) JF - Nature Communications N2 - Monolayers of transition metal dichalcogenide materials emerged as a new material class to study excitonic effects in solid state, as they benefit from enormous Coulomb correlations between electrons and holes. Especially in WSe\(_{2}\), sharp emission features have been observed at cryogenic temperatures, which act as single photon sources. Tight exciton localization has been assumed to induce an anharmonic excitation spectrum; however, the evidence of the hypothesis, namely the demonstration of a localized biexciton, is elusive. Here we unambiguously demonstrate the existence of a localized biexciton in a monolayer of WSe\(_{2}\), which triggers an emission cascade of single photons. The biexciton is identified by its time-resolved photoluminescence, superlinearity and distinct polarization in micro-photoluminescence experiments. We evidence the cascaded nature of the emission process in a cross-correlation experiment, which yields a strong bunching behaviour. Our work paves the way to a new generation of quantum optics experiments with two-dimensional semiconductors. KW - lasers KW - LED KW - quantum dots KW - light sources Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-169363 VL - 7 ER - TY - JOUR A1 - Winkler, Karol A1 - Fischer, Julian A1 - Schade, Anne A1 - Amthor, Matthias A1 - Dall, Robert A1 - Geßler, Jonas A1 - Emmerling, Monika A1 - Ostrovskaya, Elena A. A1 - Kamp, Martin A1 - Schneider, Christian A1 - Höfling, Sven T1 - A polariton condensate in a photonic crystal potential landscape JF - New Journal of Physics N2 - The possibility of investigating macroscopic coherent quantum states in polariton condensates and of engineering polariton landscapes in semiconductors has triggered interest in using polaritonic systems to simulate complex many-body phenomena. However, advanced experiments require superior trapping techniques that allow for the engineering of periodic and arbitrary potentials with strong on-site localization, clean condensate formation, and nearest-neighbor coupling. Here we establish a technology that meets these demands and enables strong, potentially tunable trapping without affecting the favorable polariton characteristics. The traps are based on a locally elongated microcavity which can be formed by standard lithography. We observe polariton condensation with non-resonant pumping in single traps and photonic crystal square lattice arrays. In the latter structures, we observe pronounced energy bands, complete band gaps, and spontaneous condensation at the M-point of the Brillouin zone. Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-125050 VL - 17 ER - 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 - Lee, Chang-Min A1 - Lim, Hee-Jin A1 - Schneider, Christian A1 - Maier, Sebastian A1 - Höfling, Sven A1 - Kamp, Martin A1 - Lee, Yong-Hee T1 - Efficient single photon source based on \(\mu\)-fibre-coupled tunable microcavity JF - Scientific Reports N2 - Efficient and fast on-demand single photon sources have been sought after as critical components of quantum information science. We report an efficient and tunable single photon source based on an InAs quantum dot (QD) embedded in a photonic crystal cavity coupled with a highly curved \(\mu\)-fibre. Exploiting evanescent coupling between the \(\mu\)-fibre and the cavity, a high collection efficiency of 23% and Purcell-enhanced spontaneous emissions are observed. In our scheme, the spectral position of a resonance can be tuned by as much as 1.5 nm by adjusting the contact position of the \(\mu\)-fibre, which increases the spectral coupling probability between the QD and the cavity mode. Taking advantage of the high photon count rate and the tunability, the collection efficiencies and the decay rates are systematically investigated as a function of the QD-cavity detuning. KW - tapers KW - semiconductor quantum dots KW - crystal KW - nanowire KW - generation KW - nanoactivity KW - mode KW - emission Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-145835 VL - 5 IS - 14309 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 - TY - JOUR A1 - Maier, Sebastian A1 - Gold, Peter A1 - Forchel, Alfred A1 - Gregersen, Niels A1 - Mork, Jesper A1 - Höfling, Sven A1 - Schneider, Christian A1 - Kamp, Martin T1 - Bright single photon source based on self-aligned quantum dot-cavity systems JF - Optics Express N2 - We report on a quasi-planar quantum-dot-based single-photon source that shows an unprecedented high extraction efficiency of 42% without complex photonic resonator geometries or post-growth nanofabrication. This very high efficiency originates from the coupling of the photons emitted by a quantum dot to a Gaussian shaped nanohill defect that naturally arises during epitaxial growth in a self-aligned manner. We investigate the morphology of these defects and characterize the photonic operation mechanism. Our results show that these naturally arising coupled quantum dot-defects provide a new avenue for efficient (up to 42% demonstrated) and pure (g(2)(0) value of 0.023) single-photon emission. KW - photon statistics KW - quantum communications KW - resonators KW - quantum-well -wire and -dot devices Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-119801 SN - 1094-4087 VL - 22 IS - 7 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 -