Time-resolved photoluminescence of single charge tuneable quantum dots allows us to probe the differences in recombination dynamics between neutral and negatively charged excitons. We find that the luminescence decay from a neutral exciton contains a second lifetime component of several nanoseconds that is not present in the luminescence from singly or doubly charged excitons. We attribute the slowly decaying component to excitation cycles in which the initial exciton formed in the dot is dark, with angular momentum M = 2, and which subsequently scatters into the bright state with M = 1. The nature of the scattering mechanism is revealed by the dependence of the lifetime on the electrical bias applied across the charge-tuneable device. That the lifetime changes by an order of magnitude within a short bias range implies that the dark-to-bright transmutation does not occur through a simple spin flip. Rather it appears to come about by the dot briefly entering a higher energy charging state which allows exchange of the existing electron with another from the n-type contact region. We model the lifetimes and relative intensities of the two decay components using a simple rate equation analysis.

We have succeeded in generating highly charged excitons in InAs self-assembled quantum dots by embedding the dots in a field-effect heterostructure. We discover an excitonic Coulomb blockage: over large regions of gate voltage, the exciton charge remains constant. We present here a summary of the emission properties of the charged excitons.

High temperature (≥ 650°C) MBE growth of A;As and AlAs/GaAs superlattices on (100) GaAs is shown to lead to quasi-periodic facetting. We demonstrate that the facetting is only due to the AlAs layers, and growth of GaAs on top of the facets replanarizes the surface. We show that the roughness between the AlAs and GaAs layers increases with increasing number of periods in the superlattice. The roughness increases to form distinct facets, which rapidly grow at the expense of the (100) surface. Within a few periods of the initial facet formation, the (100) surface has disappeared and only the facet planes are visible in cross-sectional transmission electron micrographs. At this point, the reflection high-energy electron diffraction pattern is spotty, and the specular spot is a distinct chevron. We also show that the facetting becomes more pronounced as the substrate temperature is increased from 620°C to 710°C. Atomic force micrographs show that the valleys enclosed by the facets can be several microns long, but they may also be only several nanometers long, depending on the growth conditions.

We report on the formation of lateral superlattices in short period vertical GaAs/AlAs superlattices. To explain the observed self-organized phase separation, we propose a model of vertical intermixing, driven by the exchange of Ga on the surface with impinging Al atoms. The model correctly describes the formation of lateral superlattices for both integer and fractional monolayer deposition. It also predicts a far-reaching intermixing at GaAs-AlAs interfaces. Insito RHEED studies of the initial growth stage of both GaAs-AlAs and AlAs-GaAs interfaces support the assumption of an asymmetric exchange at the growing surface and confirm the long-range Ga migration predicted by the model.

An AlxGa1−xN/GaN two-dimensional electron gas structure with x = 0.13 deposited by molecular beam epitaxy on a GaN layer grown by organometallic vapor phase epitaxy on a sapphire substrate was characterized. Hall effect measurements gave a sheet electron concentration of 5.1×1012 cm−2 and a mobility of 1.9 × 104 cm2/Vs at 10 K. Mobility spectrum analysis showed single-carrier transport and negligible parallel conduction at low temperatures. The sheet carrier concentrations determined from Shubnikov-de Haas magnetoresistance oscillations were in good agreement with the Hall data. The electron effective mass was determined to be 0.215±0.006 m0 based on the temperature dependence of the amplitude of Shubnikov-de Haas oscillations. The quantum lifetime was about one-fifth of the transport lifetime of 2.3 × 10−12 s.

A search for pair production of the supersymmetric partners of the Higgs boson (higgsinos ˜H) in gauge-mediated scenarios is reported. Each higgsino is assumed to decay to a Higgs boson and a gravitino. Two complementary analyses, targeting high- and low-mass signals, are performed to maximize sensitivity. The two analyses utilize LHC pp collision data at a center-of-mass energy √s=13  TeV, the former with an integrated luminosity of 36.1  fb−1 and the latter with 24.3  fb−1, collected with the ATLAS detector in 2015 and 2016. The search is performed in events containing missing transverse momentum and several energetic jets, at least three of which must be identified as b-quark jets. No significant excess is found above the predicted background. Limits on the cross section are set as a function of the mass of the ˜H in simplified models assuming production via mass-degenerate higgsinos decaying to a Higgs boson and a gravitino. Higgsinos with masses between 130 and 230 GeV and between 290 and 880 GeV are excluded at the 95% confidence level. Interpretations of the limits in terms of the branching ratio of the higgsino to a Z boson or a Higgs boson are also presented, and a 45% branching ratio to a Higgs boson is excluded for m˜H≈400  GeV.

V.M. Abazov, B. Abbott, B. S. Acharya, M. Adams, T. Adams, J. P. Agnew, G. D. Alexeev, G. Alkhazov, A. Alton, A. Askew, S. Atkins, K. Augsten, V. Aushev, Y. Aushev, C. Avila, F. Badaud, L. Bagby, B. Baldin, D. V. Bandurin, S. Banerjee, E. Barberis, P. Baringer, J. F. Bartlett, U. Bassler, V. Bazterra, A. Bean, M. Begalli, L. Bellantoni, S. B. Beri, G. Bernardi, R. Bernhard, I. Bertram, M. Besançon, R. Beuselinck, P. C. Bhat, S. Bhatia, V. Bhatnagar, G. Blazey, S. Blessing, K. Bloom, A. Boehnlein, D. Boline, E. E. Boos, G. Borissov, M. Borysova, A. Brandt, O. Brandt, M. Brochmann, R. Brock, A. Bross, D. Brown, X. B. Bu, M. Buehler, V. Buescher, V. Bunichev, S. Burdin, C. P. Buszello, E. Camacho-Pérez, B. C. K. Casey, H. Castilla-Valdez, S. Caughron, S. Chakrabarti, K. M. Chan, A. Chandra, E. Chapon, G. Chen, S. W. Cho, S. Choi, B. Choudhary, S. Cihangir, D. Claes, J. Clutter, M. Cooke, W. E. Cooper, M. Corcoran, F. Couderc, M.-C. Cousinou, J. Cuth, D. Cutts, A. Das, G. Davies, S. J. de Jong, E. De La Cruz-Burelo, F. Déliot, R. Demina, D. Denisov, S. P. Denisov, S. Desai, C. Deterre, K. DeVaughan, H. T. Diehl, M. Diesburg, P. F. Ding, A. Dominguez, A. Dubey, L. V. Dudko, A. Duperrin, S. Dutt, M. Eads, D. Edmunds, J. Ellison, V. D. Elvira, Y. Enari, H. Evans, A. Evdokimov, V. N. Evdokimov, A. Fauré, L. Feng, T. Ferbel, F. Fiedler, F. Filthaut, W. Fisher, H. E. Fisk, M. Fortner, H. Fox, J. Franc, S. Fuess, P. H. Garbincius, A. Garcia-Bellido, J. A. García-González, V. Gavrilov, W. Geng, C. E. Gerber, Y. Gershtein, G. Ginther, O. Gogota, G. Golovanov, P. D. Grannis, S. Greder, H. Greenlee, G. Grenier, Ph. Gris, J.-F. Grivaz, A. Grohsjean, S. Grünendahl, M.W. Grünewald, T. Guillemin, G. Gutierrez, P. Gutierrez, J. Haley, L. Han, K. Harder, A. Harel, J. M. Hauptman, J. Hays, T. Head, T. Hebbeker, D. Hedin, H. Hegab, A. P. Heinson, U. Heintz, C. Hensel, I. Heredia-De La Cruz, M. Hernández-Villanueva, K. Herner, G. Hesketh, M. D. Hildreth, R. Hirosky, T. Hoang, J. D. Hobbs, B. Hoeneisen, J. Hogan, M. Hohlfeld, J. L. Holzbauer, I. Howley, Z. Hubacek, V. Hynek, I. Iashvili, Y. Ilchenko, R. Illingworth, A. S. Ito, S. Jabeen, M. Jaffré, A. Jayasinghe, M. S. Jeong, R. Jesik, P. Jiang, K. Johns, E. Johnson, M. Johnson, A. Jonckheere, P. Jonsson, J. Joshi, A.W. Jung, A. Juste, E. Kajfasz, D. Karmanov, I. Katsanos, M. Kaur, R. Kehoe, S. Kermiche, N. Khalatyan, A. Khanov, A. Kharchilava, Y. N. Kharzheev, I. Kiselevich, J. M. Kohli, A. V. Kozelov, J. Kraus, A. Kumar, A. Kupco, T. Kurča, V. A. Kuzmin, S. Lammers, P. Lebrun, H. S. Lee, S. W. Lee, W.M. Lee, X. Lei, J. Lellouch, D. Li, H. Li, L. Li, Q. Z. Li, J. K. Lim, D. Lincoln, J. Linnemann, V. V. Lipaev, R. Lipton, H. Liu, Y. Liu, A. Lobodenko, M. Lokajicek, R. Lopes de Sa, R. Luna-Garcia, A. L. Lyon, A. K. A. Maciel, R. Madar, R. Magaña-Villalba, S. Malik, V. L. Malyshev, J. Mansour, J. Martínez-Ortega, R. McCarthy, C. L. McGivern, M. M. Meijer, A. Melnitchouk, D. Menezes, P. G. Mercadante, M. Merkin, A. Meyer, J. Meyer, F. Miconi, N. K. Mondal, M. Mulhearn, E. Nagy, M. Narain, R. Nayyar, H. A. Neal, J. P. Negret, P. Neustroev, H. T. Nguyen, T. Nunnemann, J. Orduna, N. Osman, A. Pal, N. Parashar, V. Parihar, S. K. Park, R. Partridge, N. Parua, A. Patwa, B. Penning, M. Perfilov, Y. Peters, K. Petridis, G. Petrillo, P. Pétroff, M.-A. Pleier, V. M. Podstavkov, A. V. Popov, M. Prewitt, D. Price, N. Prokopenko, J. Qian, A. Quadt, B. Quinn, P. N. Ratoff, I. Razumov, I. Ripp-Baudot, F. Rizatdinova, M. Rominsky, A. Ross, C. Royon, P. Rubinov, R. Ruchti, G. Sajot, A. Sánchez-Hernández, M. P. Sanders, A. S. Santos, G. Savage, M. Savitskyi, L. Sawyer, T. Scanlon, R. D. Schamberger, Y. Scheglov, H. Schellman, M. Schott, C. Schwanenberger, R. Schwienhorst, J. Sekaric, H. Severini, E. Shabalina, V. Shary, S. Shaw, A. A. Shchukin, V. Simak, P. Skubic, P. Slattery, G. R. Snow, J. Snow, S. Snyder, S. Söldner-Rembold, L. Sonnenschein, K. Soustruznik, J. Stark, N. Stefaniuk, D. A. Stoyanova, M. Strauss, L. Suter, P. Svoisky, M. Titov, V. V. Tokmenin, Y.-T. Tsai, D. Tsybychev, B. Tuchming, C. Tully, L. Uvarov, S. Uvarov, S. Uzunyan, R. Van Kooten, W.M. van Leeuwen, N. Varelas, E.W. Varnes, I. A. Vasilyev, A. Y. Verkheev, L. S. Vertogradov, M. Verzocchi, M. Vesterinen, D. Vilanova, P. Vokac, H. D. Wahl, M. H. L. S. Wang, J. Warchol, G. Watts, M. Wayne, J. Weichert, L. Welty-Rieger, M. R. J. Williams, G.W. Wilson, M. Wobisch, D. R. Wood, T. R. Wyatt, Y. Xie, R. Yamada, S. Yang, T. Yasuda, Y. A. Yatsunenko, W. Ye, Z. Ye, H. Yin, K. Yip, S. W. Youn, J. M. Yu, J. Zennamo, T. G. Zhao, B. Zhou, J. Zhu, M. Zielinski, D. Zieminska, and L. Zivkovic

We probe the effect of nuclear spin interaction with a resident electron spin in a quantum dot using resonance fluorescence spectroscopy and two- photon interference experiments. Screening of the nuclear field fluctuations is demonstrated to successfully generate indistinguishable single photons.

We present the first reliability study of InAs/GaAs self-assembled quantum dot lasers epitaxially grown on Ge/Si substrates. Some devices maintain lasing oscillation after more than 2700 h of constant current stress at 30 °C, longer than any previous life tests of GaAs lasers epitaxially grown on silicon. No catastrophic failures were observed. The lasers were characterized to gain insight on the aging mechanism.

We report high resolution coherent population trapping on a single hole spin in a semiconductor quantum dot. The absorption dip signifying the formation of a dark state exhibits an atomic physicslike dip width of just 10 MHz. We observe fluctuations in the absolute frequency of the absorption dip, evidence of very slow spin dephasing. We identify the cause of this process as charge noise by, first, demonstrating that the hole spin g factor in this configuration (in-plane magnetic field) is strongly dependent on the vertical electric field, and second, by characterizing the charge noise through its effects on the optical transition frequency. An important conclusion is that charge noise is an important hole spin dephasing process.

We used resonant laser spectroscopy of multiple InGaAs quantum dots to spatially locate charge fluctuators in the surrounding semiconductor matrix. By mapping out the resonance condition between a narrow-band laser and the neutral exciton transitions of individual dots in a field effect device, we identified spectral discontinuities as arising from charging and discharging events that take place within the volume adjacent to the quantum dots. Our analysis suggests that residual carbon dopants are a major source of charge-fluctuating traps in quantum dot heterostructures.

We use temporally resolved intensity cross-correlation measurements to identify the biexciton-exciton radiative cascades in a negatively charged QD. The polarization sensitive correlation measurements show unambiguously that the excited two-electron triplet states relax nonradiatively to their singlet ground state via a spin nonconserving flip-flop with the ground state heavy hole. We explain this mechanism in terms of resonant coupling between the confined electron states and an LO phonon. This resonant interaction together with the electron-hole exchange interaction provides an efficient mechanism for this otherwise spin-blockaded, electronic relaxation.

Repetitive wet thermal oxidations of a tapered oxide aperture in a micropillar structure are demonstrated. After each oxidation step the confined optical modes are analyzed at room temperature. Three regimes are identified. First, the optical confinement increases when the aperture oxidizes toward the center. Then, the cavity modes shift by more than 30 nm when the taper starts to oxidize through the center, leading to a decrease in the optical path length. Finally, the resonance frequency levels off when the aperture is oxidized all the way through the micropillar, but confined optical modes with a high quality factor remain. This repetitive oxidation technique therefore enables precise control of the optical cavity volume or wavelength.

An imaging technique is presented that enables monitoring of the wet thermal oxidation of a thin AlAs layer embedded between two distributed Bragg reflector mirrors in a micropillar. After oxidation we confirm by white light reflection spectroscopy that high quality optical modes confined to a small volume have been formed. The combination of these two optical techniques provides a reliable and efficient way of producing oxide apertured micropillar cavities for which the wet thermal oxidation is a critical fabrication step.

We experimentally characterize the spatial far-field emission profiles for the two lowest confined modes of a photonic crystal cavity of the L3 type, finding a good agreement with FDTD simulations. We then link the far-field profiles to relevant features of the cavity mode near-fields, using a simple Fabry-Perot resonator model. The effect of disorder on far-field cavity profiles is clarified through comparison between experiments and simulations. These results can be useful for emission engineering from active centers embedded in the cavity.

Surface Acoustic Waves (SAW) are employed to deliberately modify the resonator properties of a high Q photonic crystal membrane (PCM) on a semiconductor nano structure. The SAW periodically deforms the PCM, giving rise to a periodically modulated resonance position of the photonic crystal. While achieving resonance shifts exceeding Δλ = 2 nm, the quality factor of the PCM resonance remains basically unchanged. Combination of the acousto-photonic resonance modulation with single photon generation of acoustically charged quantum dots and quantum posts are discussed in the context of single photon generation of non-classical light.

Surface acoustic waves (SAWs) have proven a useful tool for dynamically manipulating the optical properties of semiconductor nanostructures. Recently we have shown that the mechanical deformation induced by a SAW on a two-dimensional photonic crystal membrane (PCM) spectrally tunes the resonance frequency of nanocavities within the PCM employing phase locked stroboscopic excitation.

We discuss the implementation of quantum information schemes with quantum dots in photonic crystal cavities, focusing on the optimization of far-field emission profiles and independent electrical tuning on quantum dots in waveguide-coupled cavities.