@article{AmthorWeissenseelFischeretal.2014, author = {Amthor, Matthias and Weißenseel, Sebastian and Fischer, Julian and Kamp, Martin and Schneider, Christian and H{\"o}fling, Sven}, title = {Electro-optical switching between polariton and cavity lasing in an InGaAs quantum well microcavity}, doi = {10.1364/OE.22.031146}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-111130}, year = {2014}, abstract = {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.}, language = {en} } @article{KimZhangWangetal.2016, author = {Kim, Seonghoon and Zhang, Bo and Wang, Zhaorong and Fischer, Julian and Brodbeck, Sebastian and Kamp, Martin and Schneider, Christian and H{\"o}fling, Sven and Deng, Hui}, title = {Coherent Polariton Laser}, series = {Physical Review X}, volume = {6}, journal = {Physical Review X}, number = {011026}, doi = {10.1103/PhysRevX.6.011026}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-166597}, year = {2016}, abstract = {The semiconductor polariton laser promises a new source of coherent light, which, compared to conventional semiconductor photon lasers, has input-energy threshold orders of magnitude lower. However, intensity stability, a defining feature of a coherent state, has remained poor. Intensity noise many times the shot noise of a coherent state has persisted, attributed to multiple mechanisms that are difficult to separate in conventional polariton systems. The large intensity noise, in turn, limits the phase coherence. Thus, the capability of the polariton laser as a source of coherence light is limited. Here, we demonstrate a polariton laser with shot-noise-limited intensity stability, as expected from a fully coherent state. This stability is achieved by using an optical cavity with high mode selectivity to enforce single-mode lasing, suppress condensate depletion, and establish gain saturation. Moreover, the absence of spurious intensity fluctuations enables the measurement of a transition from exponential to Gaussian decay of the phase coherence of the polariton laser. It suggests large self-interaction energies in the polariton condensate, exceeding the laser bandwidth. Such strong interactions are unique to matter-wave lasers and important for nonlinear polariton devices. The results will guide future development of polariton lasers and nonlinear polariton devices.}, language = {en} } @article{RauHeindelUnsleberetal.2014, author = {Rau, Markus and Heindel, Tobias and Unsleber, Sebastian and Braun, Tristan and Fischer, Julian and Frick, Stefan and Nauerth, Sebastian and Schneider, Christian and Vest, Gwenaelle and Reitzenstein, Stephan and Kamp, Martin and Forchel, Alfred and H{\"o}fling, Sven and Weinfurter, Harald}, title = {Free space quantum key distribution over 500 meters using electrically driven quantum dot single-photon sources-a proof of principle experiment}, series = {New Journal of Physics}, volume = {16}, journal = {New Journal of Physics}, number = {043003}, doi = {10.1088/1367-2630/16/4/043003}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-116760}, year = {2014}, abstract = {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.}, language = {en} } @article{WinklerFischerSchadeetal.2015, author = {Winkler, Karol and Fischer, Julian and Schade, Anne and Amthor, Matthias and Dall, Robert and Geßler, Jonas and Emmerling, Monika and Ostrovskaya, Elena A. and Kamp, Martin and Schneider, Christian and H{\"o}fling, Sven}, title = {A polariton condensate in a photonic crystal potential landscape}, series = {New Journal of Physics}, volume = {17}, journal = {New Journal of Physics}, doi = {10.1088/1367-2630/17/2/023001}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-125050}, pages = {023001}, year = {2015}, abstract = {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.}, language = {en} }