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DDC: 530 × Subject: Quantum theory ×

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    Differential Cross Sections for the H + D2 → HD(v′ = 3, j′ = 4-10) + D Reaction above the Conical Intersection
    (Washington, DC : Soc., 2015) Gao, Hong; Sneha, Mahima; Bouakline, Foudhil; Althorpe, Stuart C.; Zare, Richard N.
    We report rovibrationally selected differential cross sections (DCSs) of the benchmark reaction H + D2 → HD(v′ = 3, j′ = 4–10) + D at a collision energy of 3.26 eV, which exceeds the conical intersection of the H3 potential energy surface at 2.74 eV. We use the PHOTOLOC technique in which a fluorine excimer laser at 157.64 nm photodissociates hydrogen bromide (HBr) molecules to generate fast H atoms and the HD product is detected in a state-specific manner by resonance-enhanced multiphoton ionization. Fully converged quantum wave packet calculations were performed for this reaction at this high collision energy without inclusion of the geometric phase (GP) effect, which takes into account coupling to the first excited state of the H3 potential energy surface. Multimodal structures can be observed in most of the DCSs up to j′ = 10, which is predicted by theory and also well-reproduced by experiment. The theoretically calculated DCSs are in good overall agreement with the experimental measurements, which indicates that the GP effect is not large enough that its existence can be verified experimentally at this collision energy.
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    Experimental Observation of Dirac Nodal Links in Centrosymmetric Semimetal TiB2
    (College Park, MD : American Physical Society, 2018) Liu, Z.; Lou, R.; Guo, P.; Wang, Q.; Sun, S.; Li, C.; Thirupathaiah, S.; Fedorov, A.; Shen, D.; Liu, K.; Lei, H.; Wang, S.
    The topological nodal-line semimetal state, serving as a fertile ground for various topological quantum phases, where a topological insulator, Dirac semimetal, or Weyl semimetal can be realized when the certain protecting symmetry is broken, has only been experimentally studied in very few materials. In contrast to discrete nodes, nodal lines with rich topological configurations can lead to more unusual transport phenomena. Utilizing angle-resolved photoemission spectroscopy and first-principles calculations, here, we provide compelling evidence of nodal-line fermions in centrosymmetric semimetal TiB2 with a negligible spin-orbit coupling effect. With the band crossings just below the Fermi energy, two groups of Dirac nodal rings are clearly observed without any interference from other bands, one surrounding the Brillouin zone (BZ) corner in the horizontal mirror plane σh and the other surrounding the BZ center in the vertical mirror plane σv. The linear dispersions forming Dirac nodal rings are as wide as 2 eV. We further observe that the two groups of nodal rings link together along the Γ-K direction, composing a nodal-link configuration. The simple electronic structure with Dirac nodal links mainly constituting the Fermi surfaces suggests TiB2 as a remarkable platform for studying and applying the novel physical properties related to nodal-line fermions.
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    Seeking celestial positronium with an OH-suppressed diffraction-limited spectrograph
    (Washington, DC : The Optical Society, 2021) Robertson, Gordon; Ellis, Simon; Yu, Qingshan; Bland-Hawthorn, Joss; Betters, Christopher; Roth, Martin; Leon-Saval, Sergio
    Celestially, positronium (Ps) has been observed only through gamma-ray emission produced by its annihilation. However, in its triplet state, a Ps atom has a mean lifetime long enough for electronic transitions to occur between quantum states. This produces a recombination spectrum observable in principle at near IR wavelengths, where angular resolution greatly exceeding that of the gamma-ray observations is possible. However, the background in the near IR is dominated by extremely bright atmospheric hydroxyl (OH) emission lines. In this paper, we present the design of a diffraction-limited spectroscopic system using novel photonic components—a photonic lantern, OH fiber Bragg grating filters, and a photonic TIGER 2D pseudo-slit—to observe the Ps Balmer alpha line at 1.3122 µm for the first time, to our knowledge.
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    X-ray nanodiffraction on a single SiGe quantum dot inside a functioning field-effect transistor
    (Washington, DC : American Chemical Society, 2011) Hrauda, N.; Zhang, J.; Wintersberger, E.; Etzelstorfer, T.; Mandl, B.; Stangl, J.; Carbone, D.; Holý, V.; Jovanović, V.; Biasotto, C.; Nanver, L.K.; Moers, J.; Grützmacher, D.; Bauer, G.
    For advanced electronic, optoelectronic, or mechanical nanoscale devices a detailed understanding of their structural properties and in particular the strain state within their active region is of utmost importance. We demonstrate that X-ray nanodiffraction represents an excellent tool to investigate the internal structure of such devices in a nondestructive way by using a focused synchotron X-ray beam with a diameter of 400 nm. We show results on the strain fields in and around a single SiGe island, which serves as stressor for the Si-channel in a fully functioning Si-metal-oxide semiconductor field-effect transistor.
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    Triggered polarization-entangled photon pairs from a single quantum dot up to 30 K
    (College Park, MD : Institute of Physics Publishing, 2007) Hafenbrak, R.; Ulrich, S.M.; Michler, P.; Wang, L.; Rastelli, A.; Schmidt, O.G.
    The radiative biexciton-exciton decay in a semiconductor quantum dot (QD) has the potential of being a source of triggered polarization-entangled photon pairs. However, in most cases the anisotropy-induced exciton fine structure splitting destroys this entanglement. Here, we present measurements on improved QD structures, providing both significantly reduced inhomogeneous emission linewidths and near-zero fine structure splittings. A high-resolution detection technique is introduced which allows us to accurately determine the fine structure in the photoluminescence emission and therefore select appropriate QDs for quantum state tomography. We were able to verify the conditions of entangled or classically correlated photon pairs in full consistence with observed fine structure properties. Furthermore, we demonstrate reliable polarization-entanglement for elevated temperatures up to 30 K. The fidelity of the maximally entangled state decreases only a little from 72% at 4 K to 68% at 30 K. This is especially encouraging for future implementations in practical devices. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
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    Cold atoms in space: community workshop summary and proposed road-map
    (Berlin ; Heidelberg [u.a.] : Springer Open, 2022) Alonso, Iván; Alpigiani, Cristiano; Altschul, Brett; Araújo, Henrique; Arduini, Gianluigi; Arlt, Jan; Badurina, Leonardo; Balaž, Antun; Bandarupally, Satvika; Barish, Barry C.; Barone, Michele; Reguzzoni, Mirko; Richaud, Andrea; Riou, Isabelle; Rothacher, Markus; Roura, Albert; Ruschhaupt, Andreas; Sabulsky, Dylan O.; Safronova, Marianna; Saltas, Ippocratis D.; Bernabeu, Jose; Haehnelt, Martin; Salvi, Leonardo; Sameed, Muhammed; Saurabh, Pandey; Schäffer, Stefan; Schiller, Stephan; Schilling, Manuel; Schkolnik, Vladimir; Schlippert, Dennis; Schmidt, Piet O.; Schnatz, Harald; Hanımeli, Ekim T.; Bertoldi, Andrea; Schneider, Jean; Schneider, Ulrich; Schreck, Florian; Schubert, Christian; Shayeghi, Armin; Sherrill, Nathaniel; Shipsey, Ian; Signorini, Carla; Singh, Rajeev; Hawkins, Leonie; Singh, Yeshpal; Bingham, Robert; Skordis, Constantinos; Smerzi, Augusto; Sopuerta, Carlos F.; Sorrentino, Fiodor; Sphicas, Paraskevas; Stadnik, Yevgeny V.; Stefanescu, Petruta; Tarallo, Marco G.; Hees, Aurélien; Tentindo, Silvia; Tino, Guglielmo M.; Bize, Sébastien; Tinsley, Jonathan N.; Tornatore, Vincenza; Treutlein, Philipp; Trombettoni, Andrea; Tsai, Yu-Dai; Tuckey, Philip; Uchida, Melissa A.; Henderson, Victoria A.; Valenzuela, Tristan; Van Den Bossche, Mathias; Vaskonen, Ville; Blas, Diego; Verma, Gunjan; Vetrano, Flavio; Vogt, Christian; von Klitzing, Wolf; Waller, Pierre; Walser, Reinhold; Herr, Waldemar; Wille, Eric; Williams, Jason; Windpassinger, Patrick; Wittrock, Ulrich; Bongs, Kai; Wolf, Peter; Woltmann, Marian; Wörner, Lisa; Xuereb, André; Yahia, Mohamed; Herrmann, Sven; Yazgan, Efe; Yu, Nan; Zahzam, Nassim; Zambrini Cruzeiro, Emmanuel; Zhan, Mingsheng; Bouyer, Philippe; Zou, Xinhao; Zupan, Jure; Zupanič, Erik; Braitenberg, Carla; Hird, Thomas; Brand, Christian; Braxmaier, Claus; Bresson, Alexandre; Buchmueller, Oliver; Budker, Dmitry; Bugalho, Luís; Burdin, Sergey; Cacciapuoti, Luigi; Callegari, Simone; Calmet, Xavier; Hobson, Richard; Calonico, Davide; Canuel, Benjamin; Caramete, Laurentiu-Ioan; Carraz, Olivier; Cassettari, Donatella; Chakraborty, Pratik; Chattopadhyay, Swapan; Chauhan, Upasna; Chen, Xuzong; Chen, Yu-Ao; Hock, Vincent; Chiofalo, Maria Luisa; Coleman, Jonathon; Corgier, Robin; Cotter, J. P.; Michael Cruise, A.; Cui, Yanou; Davies, Gavin; De Roeck, Albert; Demarteau, Marcel; Derevianko, Andrei; Barsanti, Michele; Di Clemente, Marco; Djordjevic, Goran S.; Donadi, Sandro; Doré, Olivier; Dornan, Peter; Doser, Michael; Drougakis, Giannis; Dunningham, Jacob; Easo, Sajan; Eby, Joshua; Hogan, Jason M.; Elertas, Gedminas; Ellis, John; Evans, David; Examilioti, Pandora; Fadeev, Pavel; Fanì, Mattia; Fassi, Farida; Fattori, Marco; Fedderke, Michael A.; Felea, Daniel; Holst, Bodil; Feng, Chen-Hao; Ferreras, Jorge; Flack, Robert; Flambaum, Victor V.; Forsberg, René; Fromhold, Mark; Gaaloul, Naceur; Garraway, Barry M.; Georgousi, Maria; Geraci, Andrew; Holynski, Michael; Gibble, Kurt; Gibson, Valerie; Gill, Patrick; Giudice, Gian F.; Goldwin, Jon; Gould, Oliver; Grachov, Oleg; Graham, Peter W.; Grasso, Dario; Griffin, Paul F.; Israelsson, Ulf; Guerlin, Christine; Gündoğan, Mustafa; Gupta, Ratnesh K.; Jeglič, Peter; Jetzer, Philippe; Juzeliūnas, Gediminas; Kaltenbaek, Rainer; Kamenik, Jernej F.; Kehagias, Alex; Bass, Steven; Kirova, Teodora; Kiss-Toth, Marton; Koke, Sebastian; Kolkowitz, Shimon; Kornakov, Georgy; Kovachy, Tim; Krutzik, Markus; Kumar, Mukesh; Kumar, Pradeep; Lämmerzahl, Claus; Bassi, Angelo; Landsberg, Greg; Le Poncin-Lafitte, Christophe; Leibrandt, David R.; Lévèque, Thomas; Lewicki, Marek; Li, Rui; Lipniacka, Anna; Lisdat, Christian; Liu, Mia; Lopez-Gonzalez, J. L.; Battelier, Baptiste; Loriani, Sina; Louko, Jorma; Luciano, Giuseppe Gaetano; Lundblad, Nathan; Maddox, Steve; Mahmoud, M. A.; Maleknejad, Azadeh; March-Russell, John; Massonnet, Didier; McCabe, Christopher; Baynham, Charles F. A.; Meister, Matthias; Mežnaršič, Tadej; Micalizio, Salvatore; Migliaccio, Federica; Millington, Peter; Milosevic, Milan; Mitchell, Jeremiah; Morley, Gavin W.; Müller, Jürgen; Murphy, Eamonn; Beaufils, Quentin; Müstecaplıoğlu, Özgür E.; O’Shea, Val; Oi, Daniel K. L.; Olson, Judith; Pal, Debapriya; Papazoglou, Dimitris G.; Pasatembou, Elizabeth; Paternostro, Mauro; Pawlowski, Krzysztof; Pelucchi, Emanuele; Belić, Aleksandar; Pereira dos Santos, Franck; Peters, Achim; Pikovski, Igor; Pilaftsis, Apostolos; Pinto, Alexandra; Prevedelli, Marco; Puthiya-Veettil, Vishnupriya; Quenby, John; Rafelski, Johann; Rasel, Ernst M.; Bergé, Joel; Ravensbergen, Cornelis
    We summarise the discussions at a virtual Community Workshop on Cold Atoms in Space concerning the status of cold atom technologies, the prospective scientific and societal opportunities offered by their deployment in space, and the developments needed before cold atoms could be operated in space. The cold atom technologies discussed include atomic clocks, quantum gravimeters and accelerometers, and atom interferometers. Prospective applications include metrology, geodesy and measurement of terrestrial mass change due to, e.g., climate change, and fundamental science experiments such as tests of the equivalence principle, searches for dark matter, measurements of gravitational waves and tests of quantum mechanics. We review the current status of cold atom technologies and outline the requirements for their space qualification, including the development paths and the corresponding technical milestones, and identifying possible pathfinder missions to pave the way for missions to exploit the full potential of cold atoms in space. Finally, we present a first draft of a possible road-map for achieving these goals, that we propose for discussion by the interested cold atom, Earth Observation, fundamental physics and other prospective scientific user communities, together with the European Space Agency (ESA) and national space and research funding agencies.
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    Wavefunction of polariton condensates in a tunable acoustic lattice
    (Bristol : IOP, 2012) Cerda-Méndez, E.A.; Krizhanovskii, D.N.; Biermann, K.; Hey, R.; Skolnick, M.S.; Santos, P.V.
    We study the spatial coherence of polariton condensates subjected to coherent modulation by a one-dimensional tunable acoustic potential.We use an interferometric technique to measure the amplitude and phase of the macroscopic condensate wavefunction. By increasing the acoustic modulation amplitude, we track the transition from the extended wavefunction of the unperturbed condensate to a regime where the wavefunction is spatially modulated and then to a fully confined regime, where independent condensates form at the minima of the potential with negligible particle tunneling between adjacent sites.
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    Valley control by linearly polarized laser pulses: example of WSe2
    (Washington, DC : OSA, 2022) Sharma, S.; Elliott, P.; Shallcross, S.
    Electrons at the band edges of materials are endowed with a valley index, a quantum number locating the band edge within the Brillouin zone. An important question is then how this index may be controlled by laser pulses, with current understanding that it couples exclusively via circularly polarized light. Employing both tight-binding and state-of-the-art time dependent density function theory, we show that on femtosecond time scales valley coupling is a much more general effect. We find that two time separated linearly polarized pulses allow almost complete control over valley excitation, with the pulse time difference and polarization vectors emerging as key parameters for valley control. Our findings highlight the possibility of controlling coherent electronic excitation by successive femtosecond laser pulses, and offer a route towards valleytronics in two-dimensional materials.
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    Intercalant-mediated Kitaev exchange in Ag3LiIr2O6
    (College Park, MD : APS, 2022) Yadav, Ravi; Reja, Sahinur; Ray, Rajyavardhan; van den Brink, Jeroen; Nishimoto, Satoshi; Yazyev, Oleg V.
    The recently synthesized Ag3LiIr2O6 has been proposed as a Kitaev magnet in proximity to the quantum spin liquid phase. We explore its microscopic Hamiltonian and magnetic ground state using many-body quantum chemistry methods and exact diagonalization techniques. Our calculations establish a dominant bond dependent ferromagnetic Kitaev exchange between Ir sites and find that the inclusion of Ag 4d orbitals in the configuration interaction calculations strikingly enhances the Kitaev exchange. Furthermore, using exact diagonalization of the nearest-neighbor fully anisotropic J−K−Γ Hamiltonian, we obtain the magnetic phase diagram as a function of further neighbor couplings. We find that the antiferromagnetic off-diagonal coupling stabilizes long range order, but the structure factor calculations suggest that the material is very close to the quantum spin liquid phase and the ordered state can easily collapse into a liquid by small perturbations such as structural distortion or bond disorder.
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    Edge states and topological insulating phases generated by curving a nanowire with Rashba spin-orbit coupling
    (College Park : American Physical Society, 2015) Gentile, Paola; Cuoco, Mario; Ortix, Carmine
    We prove that curvature effects in low-dimensional nanomaterials can promote the generation of topological states of matter by considering the paradigmatic example of quantum wires with Rashba spin-orbit coupling, which are bent in a nanoscale periodic serpentine structure. The effect of the periodic curvature generally results in the appearance of insulating phases with a corresponding novel butterfly spectrum characterized by the formation of finite measure complex regions of forbidden energies. When the Fermi energy lies in the gaps, the system displays localized end states protected by topology. We further show that for certain superstructure periods the system possesses topologically nontrivial insulating phases at half filling. Our results suggest that the local curvature and the topology of the electronic states are inextricably intertwined in geometrically deformed nanomaterials.