Archive ouverte UNIGE | last documentshttps://archive-ouverte.unige.ch/Latest objects deposited in the Archive ouverte UNIGEengCoherence Time Extension by Large-Scale Optical Spin Polarization in a Rare-Earth Doped Crystalhttps://archive-ouverte.unige.ch/unige:142279https://archive-ouverte.unige.ch/unige:142279Optically addressable spins are actively investigated in quantum communication, processing, and sensing. Optical and spin coherence lifetimes, which determine quantum operation fidelity and storage time, are often limited by spin-spin interactions, which can be decreased by polarizing spins. Spin polarization can be achieved using optical pumping, large magnetic fields, or mK-range temperatures. Here, we show that optical pumping of a small fraction of ions with a fixed-frequency laser, coupled with spin-spin interactions and spin diffusion, leads to substantial spin polarization in a paramagnetic rare-earth doped crystal, 171Yb3+∶Y2SiO5. Indeed, more than 90% spin polarization has been achieved at 2 K and zero magnetic field. Using this spin polarization mechanism, we further demonstrate an increase in optical coherence lifetime from 0.3 ms to 0.8 ms, due to a strong decrease in spin-spin interactions. This effect opens the way to new schemes for obtaining long optical and spin coherence lifetimes in various solid-state systems such as ensembles of rare-earth ions or color centers in diamond, which are of interest for a broad range of quantum technologies.Wed, 30 Sep 2020 15:59:26 +0200Active bundles of polar and bipolar filamentshttps://archive-ouverte.unige.ch/unige:142061https://archive-ouverte.unige.ch/unige:142061Bundles of actin filaments and molecular motors of the myosin family are a common subcellular organizational motif. Typically, such bundles are under contractile stress resulting from interactions between the filaments and the motors. This holds in particular for contractile rings that appear in the late stages of cell division in animal cells and that cleave the mother into two daughter cells. It was recently shown that myosin organizes into regularly spaced clusters along rings in mammalian cells, whereas myosin clusters in fission yeast travel along the perimeter of actomyosin rings [Wollrab et al., Nat. Commun. 7, 11860 (2016)]. A mechanism based on the association of the structurally polar actin filaments into bipolar structures was shown to provide a common explanation for both observations. Here, we analyze the dynamics of this mechanism in detail. We find a rich phase diagram depending on the actomyosin interaction strength and the stability of the bipolar structures. The system can notably organize into traveling waves. Furthermore, we identify the nature of the bifurcations connecting the various patterns as parameters are changed. Finally, we report experimental patterns observed in cytokinetic rings in fission yeast and link them to solutions of our dynamic equations. Our analysis highlights the possible role played by local polarity sorting of actin filaments for the dynamics and functionality of actomyosin networks.Mon, 28 Sep 2020 12:59:01 +0200Anomalous percolation features in molecular evolutionhttps://archive-ouverte.unige.ch/unige:142059https://archive-ouverte.unige.ch/unige:142059Self-replication underlies every species of living beings and simple physical intuition dictates that some sort of autocatalysis invariably constitutes a necessary ingredient for the emergence of molecular life. This led Worst et al. [E. G. Worst, P. Zimmer, E. Wollrab, K. Kruse, and A. Ott, New J. Phys. 18, 103003 (2016)] to study a model of molecular evolution of self-replicating molecules where spontaneous ligation and simple autocatalysis are in competition for their building blocks. We revisit this model, where irreversible aggregation leads to a transition from a regime of small molecules to macromolecules, and find an array of anomalous percolation features, some of them predicted for very specific percolation processes [R. M. D'Souza and J. Nagler, Nat. Phys. 11, 531 (2015)].Mon, 28 Sep 2020 12:54:07 +0200Critical Point in Self-Organized Tissue Growthhttps://archive-ouverte.unige.ch/unige:142049https://archive-ouverte.unige.ch/unige:142049We present a theory of pattern formation in growing domains inspired by biological examples of tissue development. Gradients of signaling molecules regulate growth, while growth changes these graded chemical patterns by dilution and advection. We identify a critical point of this feedback dynamics, which is characterized by spatially homogeneous growth and proportional scaling of patterns with tissue length. We apply this theory to the biological model system of the developing wing of the fruit fly Drosophila melanogaster and quantitatively identify signatures of the critical point.Mon, 28 Sep 2020 11:35:50 +0200Sound of an axon's growthhttps://archive-ouverte.unige.ch/unige:141852https://archive-ouverte.unige.ch/unige:141852Axons are linear structures of nerve cells that can range from a few tens of micrometers up to meters in length. In addition to external cues, the length of an axon is also regulated by unknown internal mechanisms. Molecular motors have been suggested to generate oscillations with an axon-length-dependent frequency that could be used to measure an axon's extension. Here, we present a mechanism for determining the axon length that couples the mechanical properties of an axon to the spectral decomposition of the oscillatory signal.Wed, 23 Sep 2020 16:08:25 +0200Accuracy of position determination in Ca2+ signalinghttps://archive-ouverte.unige.ch/unige:141838https://archive-ouverte.unige.ch/unige:141838A living cell senses its environment and responds to external signals. In this paper, we study theoretically the precision at which cells can determine the position of a spatially localized transient extracellular signal. To this end, we focus on the case where the stimulus is converted into the release of a small molecule that acts as a second messenger, for example, Ca2+, and activates kinases that change the activity of enzymes by phosphorylating them. We analyze the spatial distribution of phosphorylation events using stochastic simulations as well as a mean-field approach. Kinases that need to bind to the cell membrane for getting activated provide more accurate estimates than cytosolic kinases. Our results could explain why the rate of Ca2+ detachment from the membrane-binding conventional protein kinase Cα is larger than its phosphorylation rate.Wed, 23 Sep 2020 15:54:45 +0200Positional Information Readout in Ca2+ Signalinghttps://archive-ouverte.unige.ch/unige:141824https://archive-ouverte.unige.ch/unige:141824Living cells respond to spatially confined signals. Intracellular signal transmission often involves the release of second messengers like Ca2+. They eventually trigger a physiological response, for example, by activating kinases that in turn activate target proteins through phosphorylation. Here, we investigate theoretically how positional information can be accurately read out by protein phosphorylation in spite of rapid second messenger diffusion. We find that accuracy is increased by binding of kinases to the cell membrane prior to phosphorylation and by increasing the rate of Ca2+ loss from the cell interior. These findings could explain some salient features of the conventional protein kinase Cα.Wed, 23 Sep 2020 15:45:33 +0200Heralded Distribution of Single-Photon Path Entanglementhttps://archive-ouverte.unige.ch/unige:141189https://archive-ouverte.unige.ch/unige:141189We report the experimental realization of heralded distribution of single-photon path entanglement at telecommunication wavelengths in a repeater-like architecture. The entanglement is established upon detection of a single photon, originating from one of two spontaneous parametric down-conversion photon pair sources, after erasing the photon’s which-path information. In order to certify the entanglement, we use an entanglement witness which does not rely on postselection. We herald entanglement between two locations, separated by a total distance of 2 km of optical fiber, at a rate of 1.6 kHz. This work paves the way towards high-rate and practical quantum repeater architectures.Mon, 14 Sep 2020 11:15:40 +0200Efficient Time-Bin Encoding for Practical High-Dimensional Quantum Key Distributionhttps://archive-ouverte.unige.ch/unige:140301https://archive-ouverte.unige.ch/unige:140301High-dimensional quantum key distribution (QKD) allows achievement of information-theoretic secure communications, providing high key-generation rates, which cannot, in principle, be obtained by QKD protocols with binary encoding. Nonetheless, the amount of experimental resources needed increases as the quantum states to be detected belong to a larger Hilbert space, thus raising the costs of practical high-dimensional systems. Here, we present an alternative scheme for fiber-based four-dimensional QKD, with time and phase encoding and one-decoy state technique. Quantum state transmission is tested over different channel lengths up to 145 km of standard single-mode fiber, evaluating the enhancement of the secret key rate in comparison to the three-state two-dimensional BB84 protocol, which is tested with the same experimental setup. Our scheme allows measurement of the four-dimensional states with a simplified and compact receiver, where only two single-photon detectors are necessary, thus making it a cost-effective solution for practical and fiber-based QKD.Wed, 26 Aug 2020 13:59:56 +0200Forces between silica particles in isopropanol solutions of 1:1 electrolyteshttps://archive-ouverte.unige.ch/unige:138566https://archive-ouverte.unige.ch/unige:138566Interactions between silica surfaces across isopropanol solutions are measured with colloidal probe technique based on atomic force microscope. In particular, the influence of 1:1 electrolytes on the interactions between silica particles is investigated. A plethora of different forces are found in these systems. Namely, van der Waals, double-layer, attractive non-Derjaguin-Landau-Verwy-Overbeek (DLVO), repulsive solvation, and damped oscillatory interactions are observed. The measured decay length of the double-layer repulsion is substantially larger than Debye lengths calculated from nominal salt concentrations. These deviations are caused by pronounced ion pairing in alcohol solutions. At separation below 10 nm, additional attractive and repulsive non-DLVO forces are observed. The former are possibly caused by charge heterogeneities induced by strong ion adsorption, whereas the latter originate from structuring of isopropanol molecules close to the surface. Finally, at increased concentrations, the transition from monotonic to damped oscillatory interactions is uncovered.Fri, 24 Jul 2020 12:29:03 +0200Quantum teleportation of single-electron stateshttps://archive-ouverte.unige.ch/unige:138222https://archive-ouverte.unige.ch/unige:138222We consider a scheme for on-demand teleportation of a dual-rail electron qubit state, based on single-electron sources and detectors. The scheme has amaximal efficiency of 25%, which is limited both by the shared entangled state as well as the Bell-state measurement. We consider two experimental implementations, realizable with current technology. The first relies on surface acoustic waves, where all the ingredients are readily available. The second is based on Lorentzian voltage pulses in quantum Hall edge channels. As single-electron detection is not yet experimentally established in these systems, we consider a tomographic detection of teleportation using current correlators up to (and including) third order. For both implementations we take into account environmental effects.Thu, 02 Jul 2020 14:31:55 +0200Properties of Neon, Magnesium, and Silicon Primary Cosmic Rays Results from the Alpha Magnetic Spectrometerhttps://archive-ouverte.unige.ch/unige:137447https://archive-ouverte.unige.ch/unige:137447We report the observation of new properties of primary cosmic rays, neon (Ne), magnesium (Mg), and silicon (Si), measured in the rigidity range 2.15 GV to 3.0 TV with 1.8 million Ne, 2.2 million Mg, and 1.6 million Si nuclei collected by the Alpha Magnetic Spectrometer experiment on the International Space Station. The Ne and Mg spectra have identical rigidity dependence above 3.65 GV. The three spectra have identical rigidity dependence above 86.5 GV, deviate from a single power law above 200 GV, and harden in an identical way. Unexpectedly, above 86.5 GV the rigidity dependence of primary cosmic rays Ne, Mg, and Si spectra is different from the rigidity dependence of primary cosmic rays He, C, and O. This shows that the Ne, Mg, and Si and He, C, and O are two different classes of primary cosmic rays.Mon, 22 Jun 2020 10:52:16 +0200Data analysis in transient electronic spectroscopy – an experimentalist's viewhttps://archive-ouverte.unige.ch/unige:137443https://archive-ouverte.unige.ch/unige:137443Time-resolved electronic spectroscopy has grown into a technique that provides hundreds to thousands of electronic spectra with femtosecond time resolution. This enables complex questions to be interrogated, with an obvious cost that the data are more detailed and thus require accurate modelling to be properly reproduced. Analysis of these data comes in a variety of forms, starting with a variety of assumptions about how the data may be decomposed. Here, four different types of analysis commonly used are discussed: band-shape analysis, global kinetic analysis, lifetime distribution models, and soft-modelling. This review provides a ?user's guide? to these various methods of data analysis, and attempts to elucidate their successes, domains in which they may be useful, and potential pitfalls in their usage.Mon, 22 Jun 2020 10:43:07 +0200Bulk and Surface Electronic Structure of the Dual-Topology Semimetal Pt2HgSe3https://archive-ouverte.unige.ch/unige:137260https://archive-ouverte.unige.ch/unige:137260abstract not availableWed, 17 Jun 2020 09:43:33 +0200First-Principles Study of Excitonic Self-Trapping in Diamondhttps://archive-ouverte.unige.ch/unige:137036https://archive-ouverte.unige.ch/unige:137036We present a first-principles study of excitonic self-trapping in diamond. Our calculation provides evidence for self-trapping of the core exciton and gives a coherent interpretation of recent experimental x-ray absorption and emission data. Self-trapping does not occur in the case of a single valence exciton. We predict, however, that self-trapping should occur in the case of a valence biexciton. This process is accompanied by a large local relaxation of the lattice which could be observed experimentally.Fri, 12 Jun 2020 14:37:42 +0200Site-specific and doping-dependent electronic structure of YBa2Cu3Ox probed by O 1s and Cu 2p x-ray-absorption spectroscopyhttps://archive-ouverte.unige.ch/unige:137032https://archive-ouverte.unige.ch/unige:137032The electronic structure of the CuO2 planes and CuO3 chains in single-domain crystals of YBa2Cu3Ox has been investigated as a function of oxygen concentration (6≤x≤7) using polarization-dependent x-ray-absorption spectroscopy of the O 1s and Cu 2p core levels. The polarization-dependent observation of unoccupied states with O and with Cu orbital character parallel to the a, b, and c axes of the crystals allows the determination of the number of hole states in Cu 3d2x-y2 and O 2px,y orbitals in the CuO2 planes as well as in Cu 3d2y-z2 and O 2py,z orbitals in the CuO3 chains. States with Cu 3d23z-r2 orbital character contribute less than 10% to the total number of states near the Fermi level. The number of holes in the planes and in the chains is found to be correlated with the superconducting transition temperature.Fri, 12 Jun 2020 14:32:50 +0200Self-testing quantum random-number generator based on an energy boundhttps://archive-ouverte.unige.ch/unige:135134https://archive-ouverte.unige.ch/unige:135134We introduce a scheme for a self-testing quantum random-number generator and demonstrate it experimentally. Compared to the fully device-independent model, our scheme requires an extra natural assumption, namely, that the mean number of photons of the signal optical modes is bounded. The scheme is self-testing, as it allows the user to verify in real time the correct functioning of the setup, hence guaranteeing the continuous generation of certified random bits. The scheme is based on a prepare-and-measure setup, which we implement in a proof-of-principle experiment using only off-the-shelf optical components. The randomness generation rate is 1.25 Mbits/s, comparable to commercial solutions. Overall, we believe that this scheme achieves a promising trade-off between the required assumptions, ease of implementation and performance.Mon, 27 Apr 2020 14:03:16 +0200Giant anomalous Hall effect in quasi-two-dimensional layered antiferromagnet Co1/3NbS2https://archive-ouverte.unige.ch/unige:134866https://archive-ouverte.unige.ch/unige:134866The discovery of the anomalous Hall effect (AHE) in bulk metallic antiferromagnets (AFMs) motivates the search of the same phenomenon in two-dimensional (2D) systems, where a quantized anomalous Hall conductance can, in principle, be observed. Here we present experiments on microfabricated devices based on Co1/3NbS2, a layered AFM that was recently found to exhibit AHE in bulk crystals below the Néel temperature TN=29 K. Transport measurements reveal a pronounced resistivity anisotropy, indicating that upon lowering temperature the electronic coupling between individual atomic layers is increasingly suppressed. The experiments also show an extremely large anomalous Hall conductivity of approximately 400 S/cm, more than one order of magnitude larger than in the bulk, which demonstrates the importance of studying the AHE in small exfoliated crystals, less affected by crystalline defects. Interestingly, the corresponding anomalous Hall conductance, when normalized to the number of contributing atomic planes, is ∼0.6e2/h per layer, approaching the value expected for the quantized anomalous Hall effect. The observed strong anisotropy of transport and the very large anomalous Hall conductance per layer make the properties of Co1/3NbS2 compatible with the presence of partially filled topologically nontrivial 2D bands originating from the magnetic superstructure of the antiferromagnetic state. Isolating atomically thin layers of this material and controlling their charge density may therefore provide a viable route to reveal the occurrence of the quantized AHE in a 2D AFM.Wed, 22 Apr 2020 13:16:40 +0200Ultrafast Spin Dynamics in Photodoped Spin-Orbit Mott Insulator Sr2IrO4https://archive-ouverte.unige.ch/unige:134512https://archive-ouverte.unige.ch/unige:134512Ultrafast photodoping of the Mott insulators, possessing strong correlation between electronic and magnetic degrees of freedom, holds promise for launching an ultrafast dynamics of spins which cannot be described in terms of conventional models of ultrafast magnetism. Here we study the ultrafast laser-induced dynamics of the magnetic order in a novel spin-orbit Mott insulator Sr2IrO4 featuring an uncompensated pattern of antiferromagnetic spin ordering. Using the transient magneto-optical Kerr effect sensitive to the net magnetization, we reveal that photodoping by femtosecond laser pulses with photon energy above the Mott gap launches melting of the antiferromagnetic order seen as ultrafast demagnetization with a characteristic time of 300 fs followed by a sub-10-ps recovery. Nonequilibrium dynamical mean-field theory calculations based on the single-band Hubbard model confirm that ultrafast demagnetization is primarily governed by the laser-induced generation of electron-hole pairs, although the precise simulated time dependencies are rather different from the experimentally observed ones. To describe the experimental results, here we suggest a phenomenological model which is based on Onsager’s formalism and accounts for the photogenerated electron-hole pairs using the concepts of holons and doublons.Tue, 14 Apr 2020 09:55:42 +0200Artificial quantum confinement in LaAlO3/SrTiO3 heterostructureshttps://archive-ouverte.unige.ch/unige:134078https://archive-ouverte.unige.ch/unige:134078Heterostructures of transition metal oxides perovskites represent an ideal platform to explore exotic phenomena involving the complex interplay between the spin, charge, orbital and lattice degrees of freedom available in these compounds. At the interface between such materials, this interplay can lead to phenomena that are present in none of the original constituents such as the formation of the interfacial two-dimensional electron system (2DES) discovered at the LaAlO3 /SrTiO 3 (LAO/STO) interface. In samples prepared by growing a LAO layer onto a STO substrate, the 2DES is confined in a band bending potential well, whose width is set by the interface charge density and the STO dielectric properties, and determines the electronic band structure. Growing LAO (2 nm) /STO (x nm)/LAO (2 nm) heterostructures on STO substrates allows us to control the extension of the confining potential of the top 2DES via the thickness of the STO layer. In such samples, we explore the electronic structure trend under an increase of the confining potential with using soft x-ray angle-resolved photoemission spectroscopy combined with ab initio calculations. The results indicate that varying the thickness of the STO film modifies the quantization of the 3d t_2g bands and, interestingly, redistributes the charge between the d_xy and d_xz/d_yz bands.Mon, 06 Apr 2020 10:43:36 +0200Autonomous multipartite entanglement engineshttps://archive-ouverte.unige.ch/unige:132258https://archive-ouverte.unige.ch/unige:132258The generation of genuine multipartite entangled states is challenging in practice. Here we explore a new route to this task, via autonomous entanglement engines which use only incoherent coupling to thermal baths and time-independent interactions. We present a general machine architecture, which allows for the generation of a broad range of multipartite entangled states in a heralded manner. Specifically, given a target multiple-qubit state, we give a sufficient condition ensuring that it can be generated by our machine. We discuss the cases of Greenberger-Horne-Zeilinger, Dicke and cluster states in detail. These results demonstrate the potential of purely thermal resources for creating multipartite entangled states useful for quantum information processing.Fri, 13 Mar 2020 14:33:48 +0100Optical Spin-Wave Storage in a Solid-State Hybridized Electron-Nuclear Spin Ensemblehttps://archive-ouverte.unige.ch/unige:132184https://archive-ouverte.unige.ch/unige:132184Solid-state impurity spins with optical control are currently investigated for quantum networks and repeaters. Among these, rare-earth-ion doped crystals are promising as quantum memories for light, with potentially long storage time, high multimode capacity, and high bandwidth. However, with spins there is often a tradeoff between bandwidth, which favors electronic spin, and memory time, which favors nuclear spins. Here, we present optical storage experiments using highly hybridized electron-nuclear hyperfine states in 171Yb3þ∶Y2SiO5, where the hybridization can potentially offer both long storage time and high bandwidth. We reach a storage time of 1.2 ms and an optical storage bandwidth of 10 MHz that is currently only limited by the Rabi frequency of the optical control pulses. The memory efficiency in this proof-of-principle demonstration was about 3%. The experiment constitutes the first optical storage using spin states in any rareearth ion with electronic spin. These results pave the way for rare-earth based quantum memories with high bandwidth, long storage time, and high multimode capacity, a key resource for quantum repeaters.Wed, 11 Mar 2020 14:02:40 +0100Physics without determinism: Alternative interpretations of classical physicshttps://archive-ouverte.unige.ch/unige:131922https://archive-ouverte.unige.ch/unige:131922Classical physics is generally regarded as deterministic, as opposed to quantum mechanics that is considered the first theory to have introduced genuine indeterminism into physics. We challenge this view by arguing that the alleged determinism of classical physics relies on the tacit, metaphysical assumption that there exists an actual value of every physical quantity, with its infinite predetermined digits (which we name principle of infinite precision). Building on recent information-theoretic arguments showing that the principle of infinite precision (which translates into the attribution of a physical meaning to mathematical real numbers) leads to unphysical consequences, we consider possible alternative indeterministic interpretations of classical physics. We also link those to well-known interpretations of quantum mechanics. In particular, we propose a model of classical indeterminism based on finite information quantities (FIQs).Moreover, we discuss the perspectives that an indeterministic physics could open (such as strong emergence), as well as some potential problematic issues. Finally, we make evident that any indeterministic interpretation of physics would have to deal with the problem of explaining how the indeterminate values become determinate, a problem known in the context of quantum mechanics as (part of) the “quantum measurement problem.” We discuss some similarities between the classical and the quantum measurement problems, and propose ideas for possible solutions (e.g., “collapse models” and “top-down causation”).Mon, 09 Mar 2020 14:35:34 +0100Complete list of tight Bell inequalities for two parties with four binary settingshttps://archive-ouverte.unige.ch/unige:131915https://archive-ouverte.unige.ch/unige:131915We give the complete list of 175 facets of the local polytope for the case where Alice and Bob each choose their measurements from a set of four binary outcome measurements. For each inequality we compute the maximum quantum violation for qubits, the resistance to noise, and the minimal detection efficiency required for closing the detection loophole with maximally entangled qubit states, in the case where both detectors have the same efficiency (symmetric case).Mon, 09 Mar 2020 14:06:05 +0100Combined sensitivity to the neutrino mass ordering with JUNO, the IceCube Upgrade, and PINGUhttps://archive-ouverte.unige.ch/unige:131864https://archive-ouverte.unige.ch/unige:131864The ordering of the neutrino mass eigenstates is one of the fundamental open questions in neutrino physics. While current-generation neutrino oscillation experiments are able to produce moderate indications on this ordering, upcoming experiments of the next generation aim to provide conclusive evidence. In this paper we study the combined performance of the two future multi-purpose neutrino oscillation experiments JUNO and the IceCube Upgrade, which employ two very distinct and complementary routes toward the neutrino mass ordering. The approach pursued by the 20 kt medium-baseline reactor neutrino experiment JUNO consists of a careful investigation of the energy spectrum of oscillated ν¯e produced by ten nuclear reactor cores. The IceCube Upgrade, on the other hand, which consists of seven additional densely instrumented strings deployed in the center of IceCube DeepCore, will observe large numbers of atmospheric neutrinos that have undergone oscillations affected by Earth matter. In a joint fit with both approaches, tension occurs between their preferred mass-squared differences Δm312=m32−m12 within the wrong mass ordering. In the case of JUNO and the IceCube Upgrade, this allows to exclude the wrong ordering at >5σ on a timescale of 3–7 years—even under circumstances that are unfavorable to the experiments’ individual sensitivities. For PINGU, a 26-string detector array designed as a potential low-energy extension to IceCube, the inverted ordering could be excluded within 1.5 years (3 years for the normal ordering) in a joint analysis.Thu, 05 Mar 2020 15:13:49 +0100Search for Magnetic Monopoles and Stable High-Electric-Charge Objects in 13 Tev Proton-Proton Collisions with the ATLAS Detectorhttps://archive-ouverte.unige.ch/unige:131179https://archive-ouverte.unige.ch/unige:131179A search for magnetic monopoles and high-electric-charge objects is presented using 34.4 fb−1 of 13 TeV pp collision data collected by the ATLAS detector at the LHC during 2015 and 2016. The considered signature is based upon high ionization in the transition radiation tracker of the inner detector associated with a pencil-shape energy deposit in the electromagnetic calorimeter. The data were collected by a dedicated trigger based on the tracker high-threshold hit capability. The results are interpreted in models of Drell-Yan pair production of stable particles with two spin hypotheses (0 and 1/2) and masses ranging from 200 to 4000 GeV. The search improves by approximately a factor of 5 the constraints on the direct production of magnetic monopoles carrying one or two Dirac magnetic charges and stable objects with electric charge in the range 20≤|z|≤60 and extends the charge range to 60<|z|≤100.Thu, 20 Feb 2020 16:33:53 +0100Measurement of neutrino and antineutrino neutral-current quasielasticlike interactions on oxygen by detecting nuclear deexcitation γ rayshttps://archive-ouverte.unige.ch/unige:128828https://archive-ouverte.unige.ch/unige:128828Neutrino- and antineutrino-oxygen neutral-current quasielasticlike interactions are measured at Super-Kamiokande using nuclear deexcitation γ rays to identify signal-like interactions in data from a 14.94(16.35)×1020 protons-on-target exposure of the T2K neutrino (antineutrino) beam. The measured flux-averaged cross sections on oxygen nuclei are ⟨σν−NCQE⟩=1.70±0.17(stat.)−0.38+0.51(syst.)×10−38 cm2/oxygen with a flux-averaged energy of 0.82 GeV and ⟨σν¯−NCQE⟩=0.98±0.16(stat.)−0.19+0.26(syst.)×10−38 cm2/oxygen with a flux-averaged energy of 0.68 GeV, for neutrinos and antineutrinos, respectively. These results are the most precise to date, and the antineutrino result is the first cross section measurement of this channel. They are compared with various theoretical predictions. The impact on evaluation of backgrounds to searches for supernova relic neutrinos at present and future water Cherenkov detectors is also discussed.Tue, 14 Jan 2020 08:39:47 +0100Vector gauge boson radiation from compact binary systems in a gauged Lμ−Lτ scenariohttps://archive-ouverte.unige.ch/unige:128827https://archive-ouverte.unige.ch/unige:128827The orbital period of a compact binary system decays mainly due to quadrupole gravitational radiation, which agrees with the observation to within 1%. Other types of radiation such as ultralight scalar or pseudoscalar radiation and massive vector boson radiation also contribute to the decay of the orbital period as long as the mass of the emitted particle is less than the orbital frequency of the compact binary system. We obtain an expression of the energy loss due to the radiation of the massive vector field from the neutron star–neutron star and neutron star–white dwarf binaries. Because of the large chemical potential of the degenerate electrons, neutron stars (NSs) have large muon charge. We derive the energy loss due to U(1)Lμ−Lτ gauge boson radiation from the binaries. For the radiation of the vector boson, the mass is restricted by MZ′<Ω≃10−19 eV, which are the orbital frequencies of the compact star binaries. Using the formula of orbital period decay, we obtain constraints on the coupling constant of the gauge boson in the gauged Lμ−Lτ theory for the four compact binary systems. For vector gauge boson muon coupling, we find that for MZ′<10−19 eV, the constraint on the coupling constant is g<O(10−20). We also obtain the exclusion plots of the massive vector Proca field and the gauge field which can couple to muons.Tue, 14 Jan 2020 08:39:47 +0100Measurements of hadron production in π++C and π++Be interactions at 60 GeV/chttps://archive-ouverte.unige.ch/unige:128826https://archive-ouverte.unige.ch/unige:128826Precise knowledge of hadron production rates in the generation of neutrino beams is necessary for accelerator-based neutrino experiments to achieve their physics goals. NA61/SHINE, a large-acceptance hadron spectrometer, has recorded hadron+nucleus interactions relevant to ongoing and future long-baseline neutrino experiments at Fermi National Accelerator Laboratory. This paper presents three analyses of interactions of 60 GeV/c π+ with thin, fixed carbon and beryllium targets. Integrated production and inelastic cross sections were measured for both of these reactions. In an analysis of strange, neutral hadron production, differential production multiplicities of KS0, Λ and Λ¯ were measured. Lastly, in an analysis of charged hadron production, differential production multiplicities of π+, π−, K+, K− and protons were measured. These measurements will enable long-baseline neutrino experiments to better constrain predictions of their neutrino flux in order to achieve better precision on their neutrino cross section and oscillation measurements.Tue, 14 Jan 2020 08:39:47 +0100Measurements of production and inelastic cross sections for p+C, p+Be, and p+Al at 60 GeV/c and p+C and p+Be at 120 GeV/chttps://archive-ouverte.unige.ch/unige:128820https://archive-ouverte.unige.ch/unige:128820This paper presents measurements of production cross sections and inelastic cross sections for the following reactions: 60 GeV/c protons with C, Be, Al targets and 120 GeV/c protons with C and Be targets. The analysis is performed using the NA61/SHINE spectrometer at the CERN Super Proton Synchrotron. First measurements are obtained using protons at 120 GeV/c, while the results for protons at 60 GeV/c are compared with previously published measurements. These interaction cross section measurements are critical inputs for neutrino flux prediction in current and future accelerator-based long-baseline neutrino experiments.Tue, 14 Jan 2020 08:39:45 +0100Constraint of the MINERνA medium energy neutrino flux using neutrino-electron elastic scatteringhttps://archive-ouverte.unige.ch/unige:128814https://archive-ouverte.unige.ch/unige:128814Elastic neutrino scattering on electrons is a precisely known purely leptonic process that provides a standard candle for measuring neutrino flux in conventional neutrino beams. Using a total sample of 810 neutrino-electron scatters after background subtraction, the measurement reduces the normalization uncertainty on the νμ NuMI beam flux between 2 and 20 GeV from 7.6 to 3.9%. This is the most precise measurement of neutrino-electron scattering to date, will reduce uncertainties on MINERνA’s absolute cross section measurements, and demonstrates a technique that can be used in future neutrino beams such as long baseline neutrino facility.Tue, 14 Jan 2020 08:39:44 +0100Measuring Higgs Couplings without Higgs Bosonshttps://archive-ouverte.unige.ch/unige:128810https://archive-ouverte.unige.ch/unige:128810The measurement of Higgs couplings constitutes an important part of present standard model precision tests at colliders. We show that modifications of Higgs couplings induce energy-growing effects in specific amplitudes involving longitudinally polarized vector bosons, and we initiate a novel program to study these effects off shell and at high energy, rather than on the Higgs resonance. Our analysis suggests that these channels are complementary and competitive with familiar on-shell measurements; moreover, they offer endless opportunities for refinement and improvements.Tue, 14 Jan 2020 08:39:44 +0100Observation of Electroweak Production of a Same-Sign W Boson Pair in Association with Two Jets in pp Collisions at √s = 13 TeV with the ATLAS Detectorhttps://archive-ouverte.unige.ch/unige:128807https://archive-ouverte.unige.ch/unige:128807This Letter presents the observation and measurement of electroweak production of a same-sign W boson pair in association with two jets using 36.1 fb−1 of proton-proton collision data recorded at a center-of-mass energy of √s = 13 TeV by the ATLAS detector at the Large Hadron Collider. The analysis is performed in the detector fiducial phase-space region, defined by the presence of two same-sign leptons, electron or muon, and at least two jets with a large invariant mass and rapidity difference. A total of 122 candidate events are observed for a background expectation of 69±7 events, corresponding to an observed signal significance of 6.5 standard deviations. The measured fiducial signal cross section is σfid=<mspace>2.89−0.48+0.51(stat)−0.28+0.29(syst) fb.Tue, 14 Jan 2020 08:39:43 +0100Search for a heavy charged boson in events with a charged lepton and missing transverse momentum from pp collisions at √s = 13 TeV with the ATLAS detectorhttps://archive-ouverte.unige.ch/unige:128800https://archive-ouverte.unige.ch/unige:128800A search for a heavy charged-boson resonance decaying into a charged lepton (electron or muon) and a neutrino is reported. A data sample of 139 fb−1 of proton-proton collisions at √s = 13 TeV collected with the ATLAS detector at the LHC during 2015–2018 is used in the search. The observed transverse mass distribution computed from the lepton and missing transverse momenta is consistent with the distribution expected from the Standard Model, and upper limits on the cross section for pp→W′→ℓν are extracted (ℓ=e or μ). These vary between 1.3 pb and 0.05 fb depending on the resonance mass in the range between 0.15 and 7.0 TeV at 95% confidence level for the electron and muon channels combined. Gauge bosons with a mass below 6.0 and 5.1 TeV are excluded in the electron and muon channels, respectively, in a model with a resonance that has couplings to fermions identical to those of the Standard Model W boson. Cross-section limits are also provided for resonances with several fixed Γ/m values in the range between 1% and 15%. Model-independent limits are derived in single-bin signal regions defined by a varying minimum transverse mass threshold. The resulting visible cross-section upper limits range between 4.6 (15) pb and 22 (22) ab as the threshold increases from 130 (110) GeV to 5.1 (5.1) TeV in the electron (muon) channel.Tue, 14 Jan 2020 08:39:41 +0100Properties of jet fragmentation using charged particles measured with the ATLAS detector in pp collisions at √s = 13 TeVhttps://archive-ouverte.unige.ch/unige:128798https://archive-ouverte.unige.ch/unige:128798This paper presents a measurement of quantities related to the formation of jets from high-energy quarks and gluons (fragmentation). Jets with transverse momentum 100 GeV <pT<2.5 TeV and pseudorapidity |η|<2.1 from an integrated luminosity of 33 fb−1 of √s = 13 TeV proton-proton collisions are reconstructed with the ATLAS detector at the Large Hadron Collider. Charged-particle tracks with pT>500 MeV and |η|<2.5 are used to probe the detailed structure of the jet. The fragmentation properties of the more forward and the more central of the two leading jets from each event are studied. The data are unfolded to correct for detector resolution and acceptance effects. Comparisons with parton shower Monte Carlo generators indicate that existing models provide a reasonable description of the data across a wide range of phase space, but there are also significant differences. Furthermore, the data are interpreted in the context of quark- and gluon-initiated jets by exploiting the rapidity dependence of the jet flavor fraction. A first measurement of the charged-particle multiplicity using model-independent jet labels (topic modeling) provides a promising alternative to traditional quark and gluon extractions using input from simulation. The simulations provide a reasonable description of the quark-like data across the jet pT range presented in -this measurement, but the gluon-like data have systematically fewer charged particles than the simulation.Tue, 14 Jan 2020 08:39:40 +0100Measurement of ν¯μ charged-current single π− production on hydrocarbon in the few-GeV region using MINERvAhttps://archive-ouverte.unige.ch/unige:128796https://archive-ouverte.unige.ch/unige:128796The antineutrino scattering channel ν¯μCH→μ+π−X (nucleon(s)) is analyzed in the incident energy range 1.5 to 10 GeV using the MINERvA detector at Fermilab. Differential cross sections are reported as functions of μ+ momentum and production angle, π− kinetic energy and production angle, and antineutrino energy and squared four-momentum transfer. Distribution shapes are generally reproduced by simulations based on the GENIE, NuWro, and GiBUU event generators, however GENIE (GiBUU) overestimates (underestimates) the cross section normalizations by 8% (10%). Comparisons of data with the GENIE-based reference simulation probe conventional treatments of cross sections and pion intranuclear rescattering. The distribution of nontrack vertex energy is used to decompose the signal sample into reaction categories, and cross sections are determined for the exclusive reactions μ+π−n and μ+π−p. A similar treatment applied to the published MINERvA sample ν¯μCH→μ+π0X[nucleon(s)] has determined the μ+π0n cross section, and the latter is used with σ(π−n) and σ(π−p) to carry out an isospin decomposition of ν¯μ-induced CC(π). The ratio of magnitudes and relative phase for isospin amplitudes A3 and A1 thereby obtained are: Rν¯=0.99±0.19 and ϕν¯=93°±7°. Our results are in agreement with bubble chamber measurements made four decades ago.Tue, 14 Jan 2020 08:39:40 +0100Axion Dark Matter Search with Interferometric Gravitational Wave Detectorshttps://archive-ouverte.unige.ch/unige:128795https://archive-ouverte.unige.ch/unige:128795Axion dark matter differentiates the phase velocities of the circular-polarized photons. In this Letter, a scheme to measure the phase difference by using a linear optical cavity is proposed. If the scheme is applied to the Fabry-Pérot arm of Advanced-LIGO-like (Cosmic-Explorer-Like) gravitational wave detector, the potential sensitivity to the axion-photon coupling constant, gaγ, reaches gaγ≃8×10−13 GeV−1(4×10−14 GeV−1) at the axion mass m≃3×10−13 eV (2×10−15 eV) and remains at around this sensitivity for three orders of magnitude in mass. Furthermore, its sensitivity has a sharp peak reaching gaγ≃10−14 GeV−1(8×10−17 GeV−1) at m=1.563×10−10 eV (1.563×10−11 eV). This sensitivity can be achieved without losing any sensitivity to gravitational waves.Tue, 14 Jan 2020 08:39:39 +0100Search for electroweak diboson production in association with a high-mass dijet system in semileptonic final states in pp collisions at √s = 13 TeV with the ATLAS detectorhttps://archive-ouverte.unige.ch/unige:128790https://archive-ouverte.unige.ch/unige:128790This paper reports on a search for electroweak diboson (WW/WZ/ZZ) production in association with a high-mass dijet system, using data from proton-proton collisions at a center-of-mass energy of √s = 13 TeV. The data, corresponding to an integrated luminosity of 35.5 fb−1, were recorded with the ATLAS detector in 2015 and 2016 at the Large Hadron Collider. The search is performed in final states in which one boson decays leptonically, and the other boson decays hadronically. The hadronically decaying W/Z boson is reconstructed as either two small-radius jets or one large-radius jet using jet substructure techniques. The electroweak production of WW/WZ/ZZ in association with two jets is measured with an observed (expected) significance of 2.7 (2.5) standard deviations, and the fiducial cross section is measured to be 45.1±8.6(stat.)−14.6+15.9(syst.) fb.Tue, 14 Jan 2020 08:39:38 +0100Observation of Light-by-Light Scattering in Ultraperipheral Pb+Pb Collisions with the ATLAS Detectorhttps://archive-ouverte.unige.ch/unige:128785https://archive-ouverte.unige.ch/unige:128785This Letter describes the observation of the light-by-light scattering process, γγ→γγ, in Pb+Pb collisions at sNN=5.02 TeV. The analysis is conducted using a data sample corresponding to an integrated luminosity of 1.73 nb−1, collected in November 2018 by the ATLAS experiment at the LHC. Light-by-light scattering candidates are selected in events with two photons produced exclusively, each with transverse energy ETγ>3 GeV and pseudorapidity |ηγ|<2.4, diphoton invariant mass above 6 GeV, and small diphoton transverse momentum and acoplanarity. After applying all selection criteria, 59 candidate events are observed for a background expectation of 12±3 events. The observed excess of events over the expected background has a significance of 8.2 standard deviations. The measured fiducial cross section is 78±13(stat)±7(syst)±3(lumi) nb.Tue, 14 Jan 2020 08:39:37 +0100Search for chargino and neutralino production in final states with a Higgs boson and missing transverse momentum at √s = 13 TeV with the ATLAS detectorhttps://archive-ouverte.unige.ch/unige:128784https://archive-ouverte.unige.ch/unige:128784A search is conducted for the electroweak pair production of a chargino and a neutralino pp→χ˜1±χ˜20, where the chargino decays into the lightest neutralino and a W boson, χ˜1±→χ˜10W±, while the neutralino decays into the lightest neutralino and a Standard Model-like 125 GeV Higgs boson, χ˜20→χ˜10h. Fully hadronic, semileptonic, diphoton, and multilepton (electrons, muons) final states with missing transverse momentum are considered in this search. Higgs bosons in the final state are identified by either two jets originating from bottom quarks (h→bb¯), two photons (h→γγ), or leptons from the decay modes h→WW, h→ZZ or h→ττ. The analysis is based on 36.1 fb−1 of √s = 13 TeV proton-proton collision data recorded by the ATLAS detector at the Large Hadron Collider. Observations are consistent with the Standard Model expectations, and 95% confidence-level limits of up to 680 GeV in χ˜1±/χ˜20 mass are set in the context of a simplified supersymmetric model.Tue, 14 Jan 2020 08:39:37 +0100Constructing effective field theories via their harmonicshttps://archive-ouverte.unige.ch/unige:128783https://archive-ouverte.unige.ch/unige:128783We consider the construction of operator bases for massless, relativistic quantum field theories, and show this is equivalent to obtaining the harmonic modes of a physical manifold (the kinematic Grassmannian), upon which observables have support. This enables us to recast the approach of effective field theory (EFT) through the lens of harmonic analysis. We explicitly construct harmonics corresponding to low mass dimension EFT operators.Tue, 14 Jan 2020 08:39:37 +0100Magnetic Monopole Search with the Full MoEDAL Trapping Detector in 13 TeV pp Collisions Interpreted in Photon-Fusion and Drell-Yan Productionhttps://archive-ouverte.unige.ch/unige:128778https://archive-ouverte.unige.ch/unige:128778MoEDAL is designed to identify new physics in the form of stable or pseudostable highly ionizing particles produced in high-energy Large Hadron Collider (LHC) collisions. Here we update our previous search for magnetic monopoles in Run 2 using the full trapping detector with almost four times more material and almost twice more integrated luminosity. For the first time at the LHC, the data were interpreted in terms of photon-fusion monopole direct production in addition to the Drell-Yan-like mechanism. The MoEDAL trapping detector, consisting of 794 kg of aluminum samples installed in the forward and lateral regions, was exposed to 4.0 fb−1 of 13 TeV proton-proton collisions at the LHCb interaction point and analyzed by searching for induced persistent currents after passage through a superconducting magnetometer. Magnetic charges equal to or above the Dirac charge are excluded in all samples. Monopole spins 0, ½, and 1 are considered and both velocity-independent and-dependent couplings are assumed. This search provides the best current laboratory constraints for monopoles with magnetic charges ranging from two to five times the Dirac charge.Tue, 14 Jan 2020 08:39:35 +0100Extensive analysis of the lattice Boltzmann method on shifted stencilshttps://archive-ouverte.unige.ch/unige:128678https://archive-ouverte.unige.ch/unige:128678Standard lattice Boltzmann methods (LBMs) are based on a symmetric discretization of the phase space, which amounts to study the evolution of particle distribution functions (PDFs) in a reference frame at rest. This choice induces a number of limitations when the simulated flow speed gets closer to the sound speed, such as velocity-dependent transport coefficients. The latter issue is usually referred to as a Galilean invariance defect. To restore the Galilean invariance of LBMs, it was proposed to study the evolution of PDFs in a comoving reference frame by relying on asymmetric shifted lattices [N. Frapolli, S. S. Chikatamarla, and I. V. Karlin, Phys. Rev. Lett. 117, 010604 (2016)]. From the numerical viewpoint, this corresponds to overcoming the rather restrictive Courant-Friedrichs-Lewy conditions on standard LBMs and modeling compressible flows while keeping memory consumption and processing costs to a minimum (therefore using the standard first-neighbor stencils). In the present work systematic physical error evaluations and stability analyses are conducted for different discrete equilibrium distribution functions (EDFs) and collision models. Thanks to them, it is possible to (1) better understand the effect of this solution on both physics and stability, (2) assess its viability as a way to extend the validity range of LBMs, and (3) quantify the importance of the reference state as compared to other parameters such as the equilibrium state and equilibration path. The results clearly show that, in theory, the concept of shifted lattices allows the scheme to deal with arbitrarily high values of the nondimensional velocity. Furthermore, just like the zero-Mach flow for the standard stencils, it is observed that setting the shift velocity to the fluid velocity results in optimal physical and numerical properties. In addition, a detailed analysis of the obtained results shows that the properties of different collision models and EDFs remain unchanged under the shift of stencil. In other words, by introducing a velocity shift in the stencil, the optimal operating point, in terms of physics and numerics, will also be shifted by the same vector regardless of the EDF or collision model considered. Eventually, while limited to the D2Q9 stencil with the nine possible first-neighbor shifts, the present study and corresponding conclusions can be extended to other stencils and velocity shifts in a straightforward manner.Mon, 13 Jan 2020 10:53:04 +0100Bulk pumping in two-dimensional topological phaseshttps://archive-ouverte.unige.ch/unige:128663https://archive-ouverte.unige.ch/unige:128663The notion of topological (Thouless) pumping in topological phases is traditionally associated with Laughlin’s pump argument for the quantization of the Hall conductance in two-dimensional (2D) quantum Hall systems. It relies on magnetic flux variations that thread the system of interest without penetrating its bulk, in the spirit of Aharonov-Bohm effects. Here we explore a different paradigm for topological pumping induced, instead, by magnetic flux variations δχ inserted through the bulk of topological phases. We show that δχ generically controls the analog of a topological pump, accompanied by robust physical phenomena. We demonstrate this concept of bulk pumping in two paradigmatic types of 2D topological phases: integer and fractional quantum Hall systems and topological superconductors. We show that bulk pumping provides a unifying connection between seemingly distinct physical effects such as density variations described by Streda’s formula in quantum Hall phases and fractional Josephson currents in topological superconductors. More importantly, we argue that bulk pumping provides a generic tool for probing topological phases and inducing robust physical effects, similar in spirit yet crucially different from Laughlin’s pump. We discuss its generalizations in other topological phases.Mon, 13 Jan 2020 09:59:06 +0100Interacting bosons in generalized zigzag and railroad-trestle modelshttps://archive-ouverte.unige.ch/unige:128662https://archive-ouverte.unige.ch/unige:128662We theoretically study the ground-state phase diagram of strongly interacting bosons on a generalized zigzag ladder model, the railroad-trestle (RRT) model. By means of analytical arguments in the limits of decoupled chains and the case of vanishing fillings as well as extensive DMRG calculations, we examine the rich interplay between frustration and interaction for various parameter regimes. We distinguish three different cases, the fully frustrated RRT model where the dispersion relation becomes doubly degenerate and an extensive chiral superfluid regime is found, the antisymmetric RRT with alternating π and 0 fluxes through the ladder plaquettes and the sawtooth limit, which is closely related to the latter case. We study detailed phase diagrams which include besides different single-component superfluids, the chiral superfluid phases, the two component superfluids, and different gaped phases, with dimer and a charge-density wave order.Mon, 13 Jan 2020 09:58:02 +0100Supersolid and pair correlations of the extended Jaynes-Cummings-Hubbard model on triangular latticeshttps://archive-ouverte.unige.ch/unige:128660https://archive-ouverte.unige.ch/unige:128660We study the extended Jaynes-Cummings-Hubbard model on triangular cavity lattices and zigzag ladders. By using density-matrix renormalization-group methods, we observe various types of solids with different density patterns and find evidence for light supersolids, which exist in extended regions of the phase diagram of the zigzag ladder. Furthermore, we observe strong pair correlations in the supersolid phase due to the interplay between the atoms in the cavities and atom-photon interaction. By means of cluster mean-field simulations and a scaling of the cluster size extending our analysis to two-dimensional triangular lattices, we present evidence for the emergence of a light supersolid in this case also.Mon, 13 Jan 2020 09:56:53 +0100Tomonaga-Luttinger Liquid Spin Dynamics in the Quasi-One-Dimensional Ising-Like Antiferromagnet BaCo2V2O8https://archive-ouverte.unige.ch/unige:128659https://archive-ouverte.unige.ch/unige:128659Combining inelastic neutron scattering and numerical simulations, we study the quasi-one-dimensional Ising anisotropic quantum antiferromagnet BaCo2V2O8 in a longitudinal magnetic field. This material shows a quantum phase transition from a Ne ́el ordered phase at zero field to a longitudinal incommensurate spin density wave at a critical magnetic field of 3.8 T. Concomitantly, the excitation gap almost closes and a fundamental reconfiguration of the spin dynamics occurs. These experimental results are well described by the universal Tomonaga-Luttinger liquid theory developed for interacting spinless fermions in one dimension. We especially observe the rise of mainly longitudinal excitations, a hallmark of the unconventional low-field regime in Ising-like quantum antiferromagnetic chains.Mon, 13 Jan 2020 09:54:54 +0100Vanishing Hall Response of Charged Fermions in a Transverse Magnetic Fieldhttps://archive-ouverte.unige.ch/unige:128658https://archive-ouverte.unige.ch/unige:128658We study the Hall response of two-dimensional lattice systems of charged fermions in a transverse magnetic field, in the ballistic coherent limit. We identify a setup in which this response vanishes over wide regions of parameter space: the “Landauer-Büttiker” setup commonly studied for coherent quantum transport, consisting of a strip contacted to biased ideal reservoirs of charges. We show that this effect does not rely on particle-hole symmetry, and is robust to a variety of perturbations including variations of the transverse magnetic field, chemical potential, and temperature. We trace this robustness back to a topological property of the Fermi surface: the number of Fermi points with positive velocity of the system. We argue that the mechanism leading to a vanishing Hall response applies to noninteracting and interacting systems alike, which we verify in concrete examples using density-matrix renormalization group simulations.Mon, 13 Jan 2020 09:53:19 +0100Universal Hall Response in Interacting Quantum Systemshttps://archive-ouverte.unige.ch/unige:128657https://archive-ouverte.unige.ch/unige:128657We theoretically study the Hall effect on interacting M-leg ladder systems, comparing different measures and properties of the zero temperature Hall response in the limit of weak magnetic fields. Focusing on SU(M) symmetric interacting bosons and fermions, as relevant for, e.g., typical synthetic dimensional quantum gas experiments, we identify an extensive regime in which the Hall imbalance ΔH is universal and corresponds to a classical Hall resistivity RH=-1/n for a large class of quantum phases. Away from this high symmetry point we observe interaction driven phenomena such as sign reversal and divergence of the Hall response.Mon, 13 Jan 2020 09:51:50 +0100Three-body constrained bosons in a double-well optical latticehttps://archive-ouverte.unige.ch/unige:128656https://archive-ouverte.unige.ch/unige:128656We analyze the ground-state properties of three-body constrained bosons in a one-dimensional optical lattice with staggered hoppings analogous to the double-well optical lattice. By considering attractive and repulsive on-site interactions between the bosons, we obtain the phase diagram which exhibits various quantum phases. Due to the double-well geometry and three-body constraint, several gapped phases such as the Mott insulators and dimer–bond-order phases emerge at commensurate densities in the repulsive interaction regime. Attractive interaction leads to the pair formation which leads to the pair–bond-order phase at unit filling, which resembles the valence-bond solid phase of composite bosonic pairs. At incommensurate densities, we see the signatures of the gapless pair superfluid phase.Mon, 13 Jan 2020 09:49:59 +0100Laser control of magnonic topological phases in antiferromagnetshttps://archive-ouverte.unige.ch/unige:128655https://archive-ouverte.unige.ch/unige:128655We study the laser control of magnon topological phases induced by the Aharonov-Casher effect in insulating antiferromagnets (AFs). Since the laser electric field can be considered as a time-periodic perturbation, we apply the Floquet theory and perform the inverse frequency expansion by focusing on the high frequency region. Using the obtained effective Floquet Hamiltonian, we study nonequilibrium magnon dynamics away from the adiabatic limit and its effect on topological phenomena. We show that a linearly polarized laser can generate helical edge magnon states and induce the magnonic spin Nernst effect, whereas a circularly polarized laser can generate chiral edge magnon states and induce the magnonic thermal Hall effect. In particular, in the latter, we find that the direction of the magnon chiral edge modes and the resulting thermal Hall effect can be controlled by the chirality of the circularly polarized laser through the change from the left-circular to the right-circular polarization. Our results thus provide a handle to control and design magnon topological properties in the insulating AF.Mon, 13 Jan 2020 09:48:51 +0100Steady states of interacting Floquet insulatorshttps://archive-ouverte.unige.ch/unige:128654https://archive-ouverte.unige.ch/unige:128654Floquet engineering offers tantalizing opportunities for controlling the dynamics of quantum many-body systems and realizing new nonequilibrium phases of matter. However, this approach faces a major challenge: generic interacting Floquet systems absorb energy from the drive, leading to uncontrolled heating which washes away the sought-after behavior. How to achieve and control a nontrivial nonequilibrium steady state is therefore of crucial importance. In this work, we study the dynamics of an interacting one-dimensional periodically driven electronic system coupled to a phonon heat bath. Using the Floquet-Boltzmann equation (FBE) we show that the electronic populations of the Floquet eigenstates can be controlled by the dissipation. We find the regime in which the steady state features an insulator-like filling of the Floquet bands, with a low density of additional excitations. Furthermore, we develop a simple rate equation model for the steady state excitation density that captures the behavior obtained from the numerical solution of the FBE over a wide range of parameters.Mon, 13 Jan 2020 09:47:46 +0100High-harmonic generation in quantum spin systemshttps://archive-ouverte.unige.ch/unige:128653https://archive-ouverte.unige.ch/unige:128653We theoretically study the high-harmonic generation (HHG) in one-dimensional spin systems. While in electronic systems the driving by ac electric fields produces radiation from the dynamics of excited charges, we consider here the situation where spin systems excited by a magnetic field pulse generate radiation via a time-dependent magnetization. Specifically, we study the magnetic dipole radiation in two types of ferromagnetic spin chain models, the Ising model with static longitudinal field and the XXZ model, and reveal the structure of the spin HHG and its relation to spin excitations. For weak laser amplitude, a peak structure appears which can be explained by time-dependent perturbation theory. With increasing amplitude, plateaus with well-defined cutoff energies emerge. In the Ising model with longitudinal field, the thresholds of the multiple plateaus in the radiation spectra can be explained by the annihilation of multiple magnons. In the XXZ model, which retains the Z2 symmetry, the laser magnetic field can induce a phase transition of the ground state when it exceeds a critical value, which results in a drastic change of the spin excitation character. As a consequence, the first cutoff energy in the HHG spectrum changes from a single-magnon to a two-magnon energy at this transition. Our results demonstrate the possibility of generating high-harmonic radiation from magnetically ordered materials and the usefulness of high-harmonic signals for extracting information on the spin excitation spectrum.Mon, 13 Jan 2020 09:46:37 +0100Polarization dependence of angle-resolved photoemission with submicron spatial resolution reveals emerging one-dimensionality of electrons in NbSe3https://archive-ouverte.unige.ch/unige:128652https://archive-ouverte.unige.ch/unige:128652In materials with nearly commensurate band filling the electron liquid may spontaneously separate into components with distinct properties, yielding complex intra- and interunit cell ordering patterns and a reduced dimensionality. Polarization-dependent angle-resolved photoemission data with submicron spatial resolution demonstrate such an electronic self-organization in NbSe3, a compound considered to be a paradigm of charge order. The new data indicate the emergence of a novel order, and reveal the one-dimensional (1D) physics hidden in a material which naively could be considered the most three dimensional of all columnar chalcogenides. The 1D physics is evidenced by a new selection rule—in two polarizations we observe two strikingly different dispersions each closely resembling apparently contradicting results of previous studies of this material.Mon, 13 Jan 2020 09:45:20 +0100Dynamics of a mobile impurity in a two-leg bosonic ladderhttps://archive-ouverte.unige.ch/unige:128650https://archive-ouverte.unige.ch/unige:128650We analyze the behavior of a mobile quantum impurity, restricted to a one-dimensional motion, in a bath formed by a two-leg bosonic ladder through a combination of field theory [Tomonaga-Luttinger liquid (TLL)] and numerical (density-matrix renormalization group) techniques. We compute the Green’s function of the impurity as a function of time at different momenta. We find a power-law decay at zero momentum, which signals the breakdown of a quasiparticle description of the impurity motion. We compute the exponent both for the limits of weak and strong impurity-bath interactions. At small impurity-bath interaction, the impurity experiences the ladder as a single channel one-dimensional bath, but with an effective coupling reduced by a factor of 2. We compare the numerical results for the exponent at zero momentum with a semianalytical expression, initially established for the chain, and find excellent agreement without adjustable parameters. We find an increase of the exponent with increasing transverse tunneling in the bath. At small tunneling, the exponent is compatible with the TLL prediction, while larger tunneling shows strong deviations. Finally, we show that, as a function of the momentum of the impurity, two different regimes of decay of the Green’s function exist, similar to the single chain case. The power-law regime occurs for small momentum, while at large momentum the Green’s function shows a faster decay, corresponding to the one expected in a polaronic regime. In this last regime, we compute the lifetime of the polaron numerically. We compute the critical momentum marking the transition between these two regimes. We compare with analytical predictions based on the structure factor of the bath and find good agreement with the numerical results. Finally, we discuss the consequences of our results for cold atomic experiments.Mon, 13 Jan 2020 09:38:43 +0100Understanding repulsively mediated superconductivity of correlated electrons via massively parallel density matrix renormalization grouphttps://archive-ouverte.unige.ch/unige:128649https://archive-ouverte.unige.ch/unige:128649The so-called minimal models of unconventional superconductivity are lattice models of interacting elec- trons derived from materials in which electron pairing arises from purely repulsive interactions. Showing unambiguously that a minimal model actually can have a superconducting ground state remains a challenge at nonperturbative interactions. We make a significant step in this direction by computing ground states of the 2D U-V Hubbard model—the minimal model of the quasi-1D superconductors—by parallelized DMRG, which allows for systematic control of any bias and that is sign-problem-free. Using distributed-memory supercomputers and leveraging the advantages of the U-V model, we can treat unprecedented sizes of 2D strips and extrapolate their spin gap both to zero approximation error and the thermodynamic limit. Our results for the spin gap are shown to be compatible with a spin excitation spectrum that is either fully gapped or has zeros only in discrete points, and conversely that a Fermi liquid or magnetically ordered ground state is incompatible with them. Coupled with the enhancement to short-range correlations that we find exclusively in the dxy pairing channel, this allows us to build an indirect case for the ground state of this model having superconducting order in the full 2D limit, and ruling out the other main possible phases, magnetic orders, and Fermi liquids.Mon, 13 Jan 2020 09:37:00 +0100Covariance Bell inequalitieshttps://archive-ouverte.unige.ch/unige:127285https://archive-ouverte.unige.ch/unige:127285We introduce Bell inequalities based on covariance, one of the most common measures of correlation. Explicit examples are discussed, and violations in quantum theory are demonstrated. A crucial feature of these covariance Bell inequalities is their nonlinearity; this has nontrivial consequences for the derivation of their local bound, which is not reached by deterministic local correlations. For our simplest inequality, we derive analytically tight bounds for both local and quantum correlations. An interesting application of covariance Bell inequalities is that they can act as "shared randomness witnesses": specifically, the value of the Bell expression gives device-independent lower bounds on both the dimension and the entropy of the shared random variable in a local model.Tue, 03 Dec 2019 14:44:28 +0100Unbounded sequence of observers exhibiting Einstein-Podolsky-Rosen steeringhttps://archive-ouverte.unige.ch/unige:127284https://archive-ouverte.unige.ch/unige:127284A sequential steering scenario is investigated, where multiple Bobs aim at demonstrating steering using successively the same half of an entangled quantum state. With isotropic entangled states of local dimension d, the number of Bobs that can steer Alice is found to be NBob∼d/logd, thus leading to an arbitrary large number of successive instances of steering with independently chosen and unbiased inputs. This scaling is achieved when considering a general class of measurements along orthonormal bases, as well as complete sets of mutually unbiased bases. Finally, we show that similar results can be obtained in an anonymous sequential scenario, where none of the Bobs know their position in the sequence.Tue, 03 Dec 2019 14:42:05 +0100Tight steering inequalities from generalized entropic uncertainty relationshttps://archive-ouverte.unige.ch/unige:127283https://archive-ouverte.unige.ch/unige:127283We establish a general connection between entropic uncertainty relations, Einstein-Podolsky-Rosen steering, and joint measurability. Specifically, we construct steering inequalities from any entropic uncertainty relation, given that the latter satisfies two natural properties. We obtain steering inequalities based on Rényi entropies. These turn out to be tight in many scenarios, using max- and min-entropy. Considering steering tests with two noisy measurements, our inequalities exactly recover the noise threshold for steerability. This is the case for any pair of qubit 2-outcome measurements, as well as for pairs of mutually unbiased bases in any dimension. This shows that easy-to-evaluate quantities such as entropy can optimally witness steering, despite the fact that they are coarse-grained representations of the underlying statistics.Tue, 03 Dec 2019 14:40:23 +0100Upper bound on certifiable randomness from a quantum black-box devicehttps://archive-ouverte.unige.ch/unige:127282https://archive-ouverte.unige.ch/unige:127282Quantum theory allows for randomness generation in a device-independent setting, where no detailed description of the experimental device is required. Here we derive a general upper bound on the amount of randomness that can be generated in such a setting. Our bound applies to any black-box scenario, thus covering a wide range of scenarios from partially characterised to completely uncharacterised devices. Specifically, we prove that the number of random bits that can be generated is limited by the number of different input states that enter the measurement device. We show explicitly that our bound is tight in the simplest case. More generally, our work indicates that the prospects of generating a large amount of randomness by using high-dimensional (or even continuous variable) systems will be extremely challenging in practice.Tue, 03 Dec 2019 14:37:18 +0100Unifying Paradigms of Quantum Refrigeration: A Universal and Attainable Bound on Coolinghttps://archive-ouverte.unige.ch/unige:127281https://archive-ouverte.unige.ch/unige:127281Cooling quantum systems is arguably one of the most important thermodynamic tasks connected to modern quantum technologies and an interesting question from a foundational perspective. It is thus of no surprise that many different theoretical cooling schemes have been proposed, differing in the assumed control paradigm and complexity, and operating either in a single cycle or in steady state limits. Working out bounds on quantum cooling has since been a highly context dependent task with multiple answers, with no general result that holds independent of assumptions. In this letter we derive a universal bound for cooling quantum systems in the limit of infinite cycles (or steady state regimes) that is valid for any control paradigm and machine size. The bound only depends on a single parameter of the refrigerator and is theoretically attainable in all control paradigms. For qubit targets we prove that this bound is achievable in a single cycle and by autonomous machines.Tue, 03 Dec 2019 14:35:05 +0100Does large quantum Fisher information imply Bell correlations?https://archive-ouverte.unige.ch/unige:127280https://archive-ouverte.unige.ch/unige:127280The quantum Fisher information (QFI) of certain multipartite entangled quantum states is larger than what is reachable by separable states, providing a metrological advantage. Are these nonclassical correlations strong enough to potentially violate a Bell inequality? Here, we present evidence from two examples. First, we discuss a Bell inequality designed for spin-squeezed states which is violated only by quantum states with a large QFI. Second, we relax a well-known lower bound on the QFI to find the Mermin Bell inequality as a special case. However, a fully general link between QFI and Bell correlations is still open.Tue, 03 Dec 2019 14:32:55 +0100Quantifying Measurement Incompatibility of Mutually Unbiased Baseshttps://archive-ouverte.unige.ch/unige:127278https://archive-ouverte.unige.ch/unige:127278Quantum measurements based on mutually unbiased bases are commonly used in quantum information processing, as they are generally viewed as being maximally incompatible and complementary. Here we quantify precisely the degree of incompatibility of mutually unbiased bases (MUB) using the notion of noise robustness. Specifically, for sets of k MUB in dimension d, we provide upper and lower bounds on this quantity. Notably, we get a tight bound in several cases, in particular for complete sets of k=d+1 MUB (given d is a prime power). On the way, we also derive a general upper bound on the noise robustness for an arbitrary set of quantum measurements. Moreover, we prove the existence of sets of k MUB that are operationally inequivalent, as they feature different noise robustness, and we provide a lower bound on the number of such inequivalent sets up to dimension 32. Finally, we discuss applications of our results for Einstein-Podolsky-Rosen steering.Tue, 03 Dec 2019 14:31:28 +0100Algorithmic construction of local models for entangled quantum states: Optimization for two-qubit stateshttps://archive-ouverte.unige.ch/unige:127275https://archive-ouverte.unige.ch/unige:127275The correlations of certain entangled quantum states can be fully reproduced via a local model. We discuss in detail the practical implementation of an algorithm for constructing local models for entangled states, recently introduced by Hirsch et al. [Phys. Rev. Lett. 117, 190402 (2016)] and Cavalcanti et al. [Phys. Rev. Lett. 117, 190401 (2016)]. The method allows one to construct both local hidden state (LHS) and local hidden variable (LHV) models, and can be applied to arbitrary entangled states in principle. Here we develop an improved implementation of the algorithm, discussing the optimization of the free parameters. For the case of two-qubit states, we design a ready-to-use optimized procedure. This allows us to construct LHS models (for projective measurements) that are almost optimal, as we show for Bell diagonal states, for which the optimal model has recently been derived. Finally, we show how to construct fully analytical local models, based on the output of the convex optimization procedure.Tue, 03 Dec 2019 14:16:51 +0100Self-testing quantum states and measurements in the prepare-and-measure scenariohttps://archive-ouverte.unige.ch/unige:127273https://archive-ouverte.unige.ch/unige:127273The goal of self-testing is to characterize an a priori unknown quantum system based solely on measurement statistics, i.e. using an uncharacterized measurement device. Here we develop self-testing methods for quantum prepare-and-measure experiments, thus not necessarily relying on entanglement and/or violation of a Bell inequality. We present noise-robust techniques for self-testing sets of quantum states and measurements, assuming an upper bound on the Hilbert space dimension. We discuss in detail the case of a 2→1 random access code with qubits, for which we provide analytically optimal self-tests. The simplicity and noise robustness of our methods should make them directly applicable to experiments.Tue, 03 Dec 2019 14:07:01 +0100Unifying paradigms of quantum refrigeration: Fundamental limits of cooling and associated work costshttps://archive-ouverte.unige.ch/unige:127271https://archive-ouverte.unige.ch/unige:127271In classical thermodynamics the work cost of control can typically be neglected. On the contrary, in quantum thermodynamics the cost of control constitutes a fundamental contribution to the total work cost. Here, focusing on quantum refrigeration, we investigate how the level of control determines the fundamental limits to cooling and how much work is expended in the corresponding process. jona{We compare two extremal levels of control. First coherent operations, where the entropy of the resource is left unchanged, and second incoherent operations, where only energy at maximum entropy (i.e. heat) is extracted from the resource. For minimal machines, we find that the lowest achievable temperature and associated work cost depend strongly on the type of control, in both single-cycle and asymptotic regimes. We also extend our analysis to general machines.} Our work provides a unified picture of the different approaches to quantum refrigeration developed in the literature, including algorithmic cooling, autonomous quantum refrigerators, and the resource theory of quantum thermodynamics.Tue, 03 Dec 2019 14:02:54 +0100Quantum measurement incompatibility does not imply Bell nonlocalityhttps://archive-ouverte.unige.ch/unige:127267https://archive-ouverte.unige.ch/unige:127267We discuss the connection between the incompatibility of quantum measurements, as captured by the notion of joint measurability, and the violation of Bell inequalities. Specifically, we present explicitly a given a set of non jointly measurable POVMs MA with the following property. Considering a bipartite Bell test where Alice uses MA, then for any possible shared entangled state ρ and any set of (possibly infinitely many) POVMs NB performed by Bob, the resulting statistics admits a local model, and can thus never violate any Bell inequality. This shows that quantum measurement incompatibility does not imply Bell nonlocality in general.Tue, 03 Dec 2019 13:42:01 +0100Characterizing Genuine Multilevel Entanglementhttps://archive-ouverte.unige.ch/unige:127266https://archive-ouverte.unige.ch/unige:127266Entanglement of high-dimensional quantum systems has become increasingly important for quantum communication and experimental tests of nonlocality. However, many effects of high-dimensional entanglement can be simulated by using multiple copies of low-dimensional systems. We present a general theory to characterize those high-dimensional quantum states for which the correlations cannot simply be simulated by low-dimensional systems. Our approach leads to general criteria for detecting multilevel entanglement in multiparticle quantum states, which can be used to verify these phenomena experimentally.Tue, 03 Dec 2019 13:39:15 +0100Properties of Cosmic Helium Isotopes Measured by the Alpha Magnetic Spectrometerhttps://archive-ouverte.unige.ch/unige:127196https://archive-ouverte.unige.ch/unige:127196Precision measurements by the Alpha Magnetic Spectrometer (AMS) on the International Space Station of 3He and 4He fluxes are presented. The measurements are based on 100 million 4He nuclei in the rigidity range from 2.1 to 21 GV and 18 million 3He from 1.9 to 15 GV collected from May 2011 to November 2017. We observed that the 3He and 4He fluxes exhibit nearly identical variations with time. The relative magnitude of the variations decreases with increasing rigidity. The rigidity dependence of the 3He/4He flux ratio is measured for the first time. Below 4 GV, the 3He/4He flux ratio was found to have a significant long-term time dependence. Above 4 GV, the 3He/4He flux ratio was found to be time independent, and its rigidity dependence is well described by a single power law proportional to R^Δ with Δ=−0.294±0.004. Unexpectedly, this value is in agreement with the B/O and B/C spectral indices at high energies.Mon, 02 Dec 2019 11:31:08 +0100Semi-device-independent characterization of quantum measurements under a minimum overlap assumptionhttps://archive-ouverte.unige.ch/unige:126558https://archive-ouverte.unige.ch/unige:126558Recently, a novel framework for semi-device-independent quantum prepare-and-measure protocols has been proposed, based on the assumption of a limited distinguishability between the prepared quantum states. Here, we discuss the problem of characterizing an unknown quantum measurement device in this setting. We present several methods to attack the problem. Considering the simplest scenario of two preparations with lower bounded overlap, we show that genuine three-outcome positive-operator valued measures (POVMs) can be certified, even in the presence of noise. Moreover, we show that the optimal POVM for performing unambiguous state discrimination can be self-tested.Wed, 20 Nov 2019 14:51:50 +0100Impact of antiferromagnetism on the optical properties of rare-earth nickelateshttps://archive-ouverte.unige.ch/unige:126556https://archive-ouverte.unige.ch/unige:126556We study the temperature dependence of the optical conductivity of rare-earth nickelate films of varying composition and strain close to the antiferromagnetic ordering temperature, TN . Two prominent peaks at 0.6 and 1.3 eV, which are characteristic of the insulating phase, display a small but significant increase in intensity when the material passes from para- to antiferromagnetic. This observation indicates the presence of a positive feedback between antiferromagnetic (AF) and bond disproportionation (BD) order. By analyzing the temperature dependence near TN , and using a Landau-type free-energy expression for BD and AF order, we infer that BD order is a necessary condition for the AF phase to appear, and that the antiferromagnetism contributes to stabilization of the bond disproportionation. This model also explains why hysteresis is particularly strong when the transition into the insulating state occurs simultaneously with antiferromagnetic orderWed, 20 Nov 2019 14:44:44 +0100Suppressed Magnetic Circular Dichroism and Valley-Selective Magnetoabsorption due to the Effective Mass Anisotropy in Bismuthhttps://archive-ouverte.unige.ch/unige:126555https://archive-ouverte.unige.ch/unige:126555We measure the far-infrared reflectivity and Kerr angle spectra on a high-quality crystal of pure semimetallic bismuth as a function of magnetic field, from which we extract the conductivity for left- and right-handed circular polarizations. The high spectral resolution allows us to separate the intraband Landau level transitions for electrons and holes. The hole transition exhibits 100% magnetic circular dichroism; it appears only for one polarization as expected for a circular cyclotron orbit. However, the dichroism for electron transitions is reduced to only 13%, which is quantitatively explained by the large effective mass anisotropy of the electron pockets of the Fermi surface. This observation is a signature of the mismatch between the metric experienced by the photons and the electrons. It allows for a contactless measurement of the effective mass anisotropy and provides a direction towards valley polarized magnetooptical pumping with elliptically polarized light.Wed, 20 Nov 2019 14:41:23 +0100Holographic imaging of the complex charge density wave order parameterhttps://archive-ouverte.unige.ch/unige:126554https://archive-ouverte.unige.ch/unige:126554The charge density wave (CDW) in solids is a collective ground state combining lattice distortions and charge ordering. It is defined by a complex order parameter with an amplitude and a phase. The amplitude and wavelength of the charge modulation are readily accessible to experiment. However, accurate measurements of the corresponding phase are significantly more challenging. Here we combine reciprocal and real space information to map the full complex order parameter based on topographic scanning tunneling microscopy (STM) images. Our technique overcomes limitations of Fourier space based techniques to achieve distinct amplitude and phase images with high spatial resolution. Applying this analysis to transition metal dichalcogenides provides striking evidence that their CDWs consist of three individual unidirectional charge modulations whose ordering vectors are connected by the fundamental rotational symmetry of the crystalline lattice. Spatial variations in the relative phases of these three modulations account for the different CDW contrasts often observed in STM topographic images. Phase images further reveal topological defects and discommensurations, a singularity predicted by theory for a nearly commensurate CDW. Such precise real space mapping of the complex order parameter provides a powerful tool for a deeper understanding of the CDW ground state whose formation mechanisms remain largely unclear.Wed, 20 Nov 2019 14:35:22 +0100Electric-Field-Effect Modulation of the Transition Temperature, Mobile Carrier Density, and In-Plane Penetration Depth of NdBa2Cu3O7−δ Thin Filmshttps://archive-ouverte.unige.ch/unige:125669https://archive-ouverte.unige.ch/unige:125669abstract not availableWed, 06 Nov 2019 16:37:13 +0100Limits on correlations in networks for quantum and no-signaling resourceshttps://archive-ouverte.unige.ch/unige:124651https://archive-ouverte.unige.ch/unige:124651A quantum network consists of independent sources distributing entangled states to distant nodes which can then perform entangled measurements, thus establishing correlations across the entire network. But how strong can these correlations be? Here we address this question, by deriving bounds on possible quantum correlations in a given network. These bounds are nonlinear inequalities that depend only on the topology of the network. We discuss in detail the notably challenging case of the triangle network. Moreover, we conjecture that our bounds hold in general no-signaling theories. In particular, we prove that our inequalities for the triangle network hold when the sources are arbitrary no-signaling boxes which can be wired together. Finally, we discuss an application of our results for the device-independent characterization of the topology of a quantum network.Mon, 21 Oct 2019 11:42:02 +0200Enabling computation of correlation bounds for finite-dimensional quantum systems via symmetrisationhttps://archive-ouverte.unige.ch/unige:124650https://archive-ouverte.unige.ch/unige:124650We present a technique for reducing the computational requirements by several orders of magnitude in the evaluation of semidefinite relaxations for bounding the set of quantum correlations arising from finite-dimensional Hilbert spaces. The technique, which we make publicly available through a user-friendly software package, relies on the exploitation of symmetries present in the optimisation problem to reduce the number of variables and the block sizes in semidefinite relaxations. It is widely applicable in problems encountered in quantum information theory and enables computations that were previously too demanding. We demonstrate its advantages and general applicability in several physical problems. In particular, we use it to robustly certify the non-projectiveness of high-dimensional measurements in a black-box scenario based on self-tests of $d$-dimensional symmetric informationally complete POVMs.Mon, 21 Oct 2019 11:40:27 +0200Self-testing entangled measurements in quantum networkshttps://archive-ouverte.unige.ch/unige:124649https://archive-ouverte.unige.ch/unige:124649Self-testing refers to the possibility of characterizing an unknown quantum device based only on the observed statistics. Here we develop methods for self-testing entangled quantum measurements, a key element for quantum networks. Our approach is based on the natural assumption that separated physical sources in a network should be considered independent. This provides a natural formulation of the problem of certifying entangled measurements. Considering the setup of entanglement swapping, we derive a robust self-test for the Bell-state measurement, tolerating noise levels up to 5%. We also discuss generalizations to other entangled measurements.Mon, 21 Oct 2019 11:39:13 +0200Semi-device-independent characterisation of multipartite entangled states and measurementshttps://archive-ouverte.unige.ch/unige:124648https://archive-ouverte.unige.ch/unige:124648The semi-device-independent framework allows one to draw conclusions about properties of an unknown quantum system under weak assumptions. Here we present a semi-device-independent scheme for the characterisation of multipartite entanglement based around a game played by several isolated parties whose devices are uncharacterised beyond an assumption about the dimension of their Hilbert spaces. Our scheme can certify that an $n$-partite high-dimensional quantum state features genuine multipartite entanglement. Moreover, the scheme can certify that a joint measurement on $n$ subsystems is entangled, and provides a lower bound on the number of entangled measurement operators. These tests are strongly robust to noise, and even optimal for certain classes of states and measurements, as we demonstrate with illustrative examples. Notably, our scheme allows for the certification of many entangled states admitting a local model, which therefore cannot violate any Bell inequality.Mon, 21 Oct 2019 11:37:08 +0200All entangled pure quantum states violate the bilocality inequalityhttps://archive-ouverte.unige.ch/unige:124644https://archive-ouverte.unige.ch/unige:124644The nature of quantum correlations in networks featuring independent sources of entanglement remains poorly understood. Here, focusing on the simplest network of entanglement swapping, we start a systematic characterization of the set of quantum states leading to violation of the so-called "bilocality" inequality. First, we show that all possible pairs of entangled pure states can violate the inequality. Next, we derive a general criterion for violation for arbitrary pairs of mixed two-qubit states. Notably, this reveals a strong connection between the CHSH Bell inequality and the bilocality inequality, namely that any entangled state violating CHSH also violates the bilocality inequality. We conclude with a list of open questions.Mon, 21 Oct 2019 11:30:07 +0200Genuine quantum nonlocality in the triangle networkhttps://archive-ouverte.unige.ch/unige:124643https://archive-ouverte.unige.ch/unige:124643Quantum networks allow in principle for completely novel forms of quantum correlations. In particular, quantum nonlocality can be demonstrated here without the need of having various input settings, but only by considering the joint statistics of fixed local measurement outputs. However, previous examples of this intriguing phenomenon all appear to stem directly from the usual form of quantum nonlocality, namely via the violation of a standard Bell inequality. Here we present novel examples of 'quantum nonlocality without inputs', which we believe represent a new form of quantum nonlocality, genuine to networks. Our simplest examples, for the triangle network, involve both entangled states and joint entangled measurements. A generalization to any odd-cycle network is also presented. Finally, we conclude with some open questions.Mon, 21 Oct 2019 11:27:56 +0200Momentum-resolved lattice dynamics of parent and electron-doped Sr2IrO4https://archive-ouverte.unige.ch/unige:123135https://archive-ouverte.unige.ch/unige:123135The mixing of orbital and spin character in the wave functions of the 5d iridates has led to predictions of strong couplings among their lattice, electronic, and magnetic degrees of freedom. As well as realizing a novel spin-orbit assisted Mott-insulating ground state, the perovskite iridate Sr2IrO4 has strong similarities with the cuprate La2CuO4, which on doping hosts a charge-density wave that appears intimately connected to high-temperature superconductivity. These phenomena can be sensitively probed through momentum-resolved measurements of the lattice dynamics, made possible by meV-resolution inelastic x-ray scattering. Here we report the first such measurements for both parent and electron-doped Sr2IrO4. We find that the low-energy phonon dispersions and intensities in both compounds are well described by the same nonmagnetic density functional theory calculation. In the parent compound, no changes of the phonons on magnetic ordering are discernible within the experimental resolution, and in the doped compound no anomalies are apparent due to charge-density waves. These measurements extend our knowledge of the lattice properties of (Sr1−xLax)2IrO4 and constrain the couplings of the phonons to magnetic and charge order.Fri, 13 Sep 2019 15:14:30 +0200High-Resolution Photoemission on Sr2RuO4 Reveals Correlation-Enhanced Effective Spin-Orbit Coupling and Dominantly Local Self-Energieshttps://archive-ouverte.unige.ch/unige:123134https://archive-ouverte.unige.ch/unige:123134We explore the interplay of electron-electron correlations and spin-orbit coupling in the model Fermi liquid Sr2RuO4 using laser-based angle-resolved photoemission spectroscopy. Our precise measurement of the Fermi surface confirms the importance of spin-orbit coupling in this material and reveals that its effective value is enhanced by a factor of about 2, due to electronic correlations. The self-energies for the β and γ sheets are found to display significant angular dependence. By taking into account the multi-orbital composition of quasiparticle states, we determine self-energies associated with each orbital component directly from the experimental data. This analysis demonstrates that the perceived angular dependence does not imply momentum-dependent many-body effects but arises from a substantial orbital mixing induced by spin-orbit coupling. A comparison to single-site dynamical mean-field theory further supports the notion of dominantly local orbital self-energies and provides strong evidence for an electronic origin of the observed nonlinear frequency dependence of the self-energies, leading to “kinks” in the quasiparticle dispersion of Sr2RuO4.Fri, 13 Sep 2019 15:08:21 +0200Enhanced Electron-Phonon Interaction in Multivalley Materialshttps://archive-ouverte.unige.ch/unige:121684https://archive-ouverte.unige.ch/unige:121684We report a combined experimental and theoretical investigation that reveals a new mechanism responsible for the enhancement of electron-phonon coupling in doped semiconductors in which multiple inequivalent valleys are simultaneously populated. Using Raman spectroscopy on ionic-liquid-gated monolayer and bilayer MoS2, WS2, and WSe2 over a wide range of electron and hole densities, we find that phonons with a dominant out-of-plane character exhibit strong softening upon electron accumulation while remaining unaffected upon hole doping. This unexpected—but very pronounced—electron-hole asymmetry is systematically observed in all monolayers and bilayers. By performing first-principles simulations, we show that the phonon softening occurs when multiple inequivalent valleys are populated simultaneously. Accordingly, the observed electron-hole asymmetry originates from the much larger energy separation between valleys in the valence bands—as compared to the conduction band—that prevents the population of multiple valleys upon hole accumulation. We infer that the enhancement of the electron-phonon coupling occurs because the population of multiple valleys acts to strongly reduce the efficiency of electrostatic screening for those phonon modes that cause the energy of the inequivalent valleys to oscillate out of phase. This robust mechanism is likely to play an important role in several physical phenomena, possibly including the occurrence of superconductivity in different transition metal dichalcogenides.Tue, 20 Aug 2019 09:18:07 +0200Single-spectrum prediction of kurtosis of water waves in a non-conservative modelhttps://archive-ouverte.unige.ch/unige:121099https://archive-ouverte.unige.ch/unige:121099We study statistical properties after a sudden episode of wind for water waves propagating in one direction. A wave with random initial conditions is propagated using a forced-damped higher order Nonlinear Schr"odinger equation (NLS). During the wind episode, the wave action increases, the spectrum broadens, the spectral mean shifts up and the Benjamin-Feir index (BFI) and the kurtosis increase. Conversely, after the wind episode, the opposite occurs for each quantity. The kurtosis of the wave height distribution is considered the main parameter that can indicate whether rogue waves are likely to occur in a sea state, and the BFI is often mentioned as a means to predict the kurtosis. However, we find that while there is indeed a quadratic relation between these two, this relationship is dependent on the details of the forcing and damping. Instead, a simple and robust quadratic relation does exist between the kurtosis and the bandwidth. This could allow for a single-spectrum assessment of the likelihood of rogue waves in a given sea state. In addition, as the kurtosis depends strongly on the damping and forcing coefficients, by combining the bandwidth measurement with the damping coefficient, the evolution of the kurtosis after the wind episode can be predicted.Tue, 23 Jul 2019 10:28:30 +0200Characterization of flow reduction properties in an aneurysm due to a stenthttps://archive-ouverte.unige.ch/unige:120888https://archive-ouverte.unige.ch/unige:120888We consider a lattice Boltzmann simulation of blood flow in a vessel deformed by the presence of an aneurysm. Modern clinical treatments involve introducing a stent (a tubular mesh of wires) into the cerebral artery in order to reduce the flow inside the aneurysm and favor its spontaneous reabsorption. A crucial question is to design the stent with suitable porosity so as to produce the most effective flow reduction. We propose a stent positioning factor as a characterizing tool for stent pore design in order to describe the flow reduction effect and reveal the several flow reduction mechanisms using this effect.Wed, 17 Jul 2019 15:44:36 +0200Theory and applications of an alternative lattice Boltzmann grid refinement algorithmhttps://archive-ouverte.unige.ch/unige:120658https://archive-ouverte.unige.ch/unige:120658This contribution proposes an alternative lattice Boltzmann grid refinement algorithm that overcomes the drawbacks that plague existing approaches. We demonstrate that this algorithm is accurate and applicable for all values of the relaxation time. We also show that this algorithm can significantly speed up the flow settlement process. By using a hierarchy of grid levels, the stationary regime can be approached up to a thousand times faster than with a single grid resolution.Fri, 12 Jul 2019 13:58:10 +0200Combination of Searches for Invisible Higgs Boson Decays with the ATLAS Experimenthttps://archive-ouverte.unige.ch/unige:120307https://archive-ouverte.unige.ch/unige:120307Dark matter particles, if sufficiently light, may be produced in decays of the Higgs boson. This Letter presents a statistical combination of searches for H→invisible decays where H is produced according to the standard model via vector boson fusion, Z(ℓℓ)H, and W/Z(had)H, all performed with the ATLAS detector using 36.1 fb−1 of pp collisions at a center-of-mass energy of s=13 TeV at the LHC. In combination with the results at s=7 and 8 TeV, an exclusion limit on the H→invisible branching ratio of 0.26(0.17−0.05+0.07) at 95% confidence level is observed (expected).Tue, 02 Jul 2019 17:16:08 +0200Ab-initio calculations of laser-atom interactions reveal harmonics feedback during macroscopic propagationhttps://archive-ouverte.unige.ch/unige:119874https://archive-ouverte.unige.ch/unige:119874We couple the full 3D ab initio quantum evolution of the light pulse polarization in interaction with an atom with a propagation model to simulate the propagation of ultrashort laser pulses over macroscopic dimensions, in the presence of self-generated harmonics up to order 11. We evidence a clear feedback of the generated harmonics on propagation, with an influence on the ionization probability as well as the yield of the harmonic generation itself.Mon, 24 Jun 2019 11:21:34 +0200Field-induced anisotropy in the quasi-two-dimensional weakly anisotropic antiferromagnet [CuCl(pyz)2]BF4https://archive-ouverte.unige.ch/unige:119081https://archive-ouverte.unige.ch/unige:119081We measured NMR and magnetic susceptibility for the quasi-two-dimensional, weakly XY-like, spin-1/2 square-lattice Heisenberg antiferromagnet [CuCl(pyz)<sub>2</sub>]BF<sub>4</sub> (pyz = pyrazine = N<sub>2</sub>C<sub>4<sub>H<sub>4</sub>) near the critical temperature. The Néel temperature T<sub>N</sub> and the order-parameter critical exponent β were obtained from the NMR line broadening as a function of temperature. As the applied field strength (H||c) was increased, T<sub>N</sub> increased and β decreased. This behavior indicates that the field effectively enhanced XY anisotropy. The susceptibility as a function of temperature did not show a clear feature for T<sub>N</sub>, but showed field-dependent minima below T<sub>N</sub> for both H || c and H || ab, where minimum features disappeared for μ<sub>0</sub>H > 2T.Tue, 11 Jun 2019 13:17:40 +0200Measurement of the tt¯Z and tt¯W cross sections in proton-proton collisions at √s = 13 TeV with the ATLAS detectorhttps://archive-ouverte.unige.ch/unige:118813https://archive-ouverte.unige.ch/unige:118813A measurement of the associated production of a top-quark pair (tt¯) with a vector boson (W, Z) in proton-proton collisions at a center-of-mass energy of 13 TeV is presented, using 36.1 fb−1 of integrated luminosity collected by the ATLAS detector at the Large Hadron Collider. Events are selected in channels with two same- or opposite-sign leptons (electrons or muons), three leptons or four leptons, and each channel is further divided into multiple regions to maximize the sensitivity of the measurement. The tt¯Z and tt¯W production cross sections are simultaneously measured using a combined fit to all regions. The best-fit values of the production cross sections are σtt¯Z=0.95±0.08stat±0.10syst pb and σtt¯W=0.87±0.13stat±0.14syst pb in agreement with the Standard Model predictions. The measurement of the tt¯Z cross section is used to set constraints on effective field theory operators which modify the tt¯Z vertex.Tue, 04 Jun 2019 17:13:21 +0200Search for light sterile neutrinos with the T2K far detector Super-Kamiokande at a baseline of 295 kmhttps://archive-ouverte.unige.ch/unige:118812https://archive-ouverte.unige.ch/unige:118812We perform a search for light sterile neutrinos using the data from the T2K far detector at a baseline of 295 km, with an exposure of 14.7(7.6)×1020 protons on target in neutrino (antineutrino) mode. A selection of neutral-current interaction samples is also used to enhance the sensitivity to sterile mixing. No evidence of sterile neutrino mixing in the 3+1 model was found from a simultaneous fit to the charged-current muon, electron and neutral-current neutrino samples. We set the most stringent limit on the sterile oscillation amplitude sin2θ24 for the sterile neutrino mass splitting Δm412<3×10−3 eV2/c4.Tue, 04 Jun 2019 17:13:21 +0200FASER’s physics reach for long-lived particleshttps://archive-ouverte.unige.ch/unige:118800https://archive-ouverte.unige.ch/unige:118800The ForwArd Search ExpeRiment (FASER) is an approved experiment dedicated to searching for light, extremely weakly interacting particles at the LHC. Such particles may be produced in the LHC’s high-energy collisions and travel long distances through concrete and rock without interacting. They may then decay to visible particles in FASER, which is placed 480 m downstream of the ATLAS interaction point. In this work we briefly describe the FASER detector layout and the status of potential backgrounds. We then present the sensitivity reach for FASER for a large number of long-lived particle models, updating previous results to a uniform set of detector assumptions, and analyzing new models. In particular, we consider all of the renormalizable portal interactions, leading to dark photons, dark Higgs bosons, and heavy neutral leptons; light B−L and Li−Lj gauge bosons; axionlike particles that are coupled dominantly to photons, fermions, and gluons through nonrenormalizable operators; and pseudoscalars with Yukawa-like couplings. We find that FASER and its follow-up, FASER 2, have a full physics program, with discovery sensitivity in all of these models and potentially far-reaching implications for particle physics and cosmology.Tue, 04 Jun 2019 17:13:09 +0200Search for heavy particles decaying into a top-quark pair in the fully hadronic final state in pp collisions at √s = 13 TeV with the ATLAS detectorhttps://archive-ouverte.unige.ch/unige:118799https://archive-ouverte.unige.ch/unige:118799A search for new particles decaying into a pair of top quarks is performed using proton-proton collision data recorded with the ATLAS detector at the Large Hadron Collider at a center-of-mass energy of s=13 TeV corresponding to an integrated luminosity of 36.1 fb−1. Events consistent with top-quark pair production and the fully hadronic decay mode of the top quarks are selected by requiring multiple high transverse momentum jets including those containing b-hadrons. Two analysis techniques, exploiting dedicated top-quark pair reconstruction in different kinematic regimes, are used to optimize the search sensitivity to new hypothetical particles over a wide mass range. The invariant mass distribution of the two reconstructed top-quark candidates is examined for resonant production of new particles with various spins and decay widths. No significant deviation from the Standard Model prediction is observed and limits are set on the production cross-section times branching fraction for new hypothetical Z′ bosons, dark-matter mediators, Kaluza-Klein gravitons and Kaluza-Klein gluons. By comparing with the predicted production cross sections, the Z′ boson in the topcolor-assisted-technicolor model is excluded for masses up to 3.1–3.6 TeV, the dark-matter mediators in a simplified framework are excluded in the mass ranges from 0.8 to 0.9 TeV and from 2.0 to 2.2 TeV, and the Kaluza-Klein gluon is excluded for masses up to 3.4 TeV, depending on the decay widths of the particles.Tue, 04 Jun 2019 17:13:09 +0200Search for heavy charged long-lived particles in the ATLAS detector in 36.1 fb−1 of proton-proton collision data at √s = 13 TeVhttps://archive-ouverte.unige.ch/unige:118797https://archive-ouverte.unige.ch/unige:118797A search for heavy charged long-lived particles is performed using a data sample of 36.1 fb−1 of proton-proton collisions at s=13 TeV collected by the ATLAS experiment at the Large Hadron Collider. The search is based on observables related to ionization energy loss and time of flight, which are sensitive to the velocity of heavy charged particles traveling significantly slower than the speed of light. Multiple search strategies for a wide range of lifetimes, corresponding to path lengths of a few meters, are defined as model independently as possible, by referencing several representative physics cases that yield long-lived particles within supersymmetric models, such as gluinos/squarks (R-hadrons), charginos and staus. No significant deviations from the expected Standard Model background are observed. Upper limits at 95% confidence level are provided on the production cross sections of long-lived R-hadrons as well as directly pair-produced staus and charginos. These results translate into lower limits on the masses of long-lived gluino, sbottom and stop R-hadrons, as well as staus and charginos of 2000, 1250, 1340, 430, and 1090 GeV, respectively.Tue, 04 Jun 2019 17:13:07 +0200Low-dimensional correlations under thermal fluctuationshttps://archive-ouverte.unige.ch/unige:118725https://archive-ouverte.unige.ch/unige:118725We study the correlation functions of quantum spin 1/2 ladders at finite temperature, under a magnetic field, in the gapless phase at various relevant temperatures T≠0, momentum q and frequencies ω. We compute those quantities using the time dependent density matrix renormalization group (T-DMRG) in some optimal numerical scheme. We compare these correlations with the ones of dimerized quantum spin chains and simple spin chains, that we compute by a similar technique. We analyze the intermediate energy modes and show that the effect of temperature lead to the formation of an essentially dispersive mode corresponding to the propagation of a triplet mode in an incoherent background, with a dispersion quite different from the one occurring at very low temperatures. We compare the low energy part of the spectrum with the predictions of the Tomonaga-Luttinger liquid field theory at finite temperature. We shows that the field theory describes in a remarkably robust way the low energy correlations for frequencies or temperatures up to the natural cutoff (the effective dispersion) of the system. We discuss how our results could be tested in e.g. neutron scattering experiments.Tue, 04 Jun 2019 14:38:43 +0200Ab Initio Molecular Dynamics for d-Electron Systems: Liquid Copper at 1500 Khttps://archive-ouverte.unige.ch/unige:117890https://archive-ouverte.unige.ch/unige:117890We show than an ab initio molecular-dynamics scheme based on Vanderbilt ultrasoft pseudopotentials and a plane-wave expansion for the electronic orbitals allows one to perform accurate calculations for large systems containing tightly bound d-electron states. We use a novel real-space double-grid technique to deal efficiently with the localized augmentation functions in the core region. We apply our scheme in a full molecular-dynamics simulation of liquid copper at a temperature of 1500 K and find structural and dynamical properties that are in excellent agreement with experimental data.Tue, 21 May 2019 14:29:42 +0200Si 2p Core-Level Shifts at the Si(001)-SiO2 Interface: a First-Principles Studyhttps://archive-ouverte.unige.ch/unige:117886https://archive-ouverte.unige.ch/unige:117886Using a first-principles approach, we calculate core-level shifts at the Si(001)-SiO₂ interface. By fully relaxing interfaces between Si and tridymite, a crystalline form of SiO₂, we obtain interface models with good local structural properties and with no electronic states in the Si gap. Calculated values of Si 2p core-level shifts agree well with data from photoemission experiments and show a linear dependence on the number of nearest-neighbor oxygen atoms. Core-hole relaxation accounts for ∼50% of the total shifts, in good agreement with Auger experiments.Tue, 21 May 2019 14:27:17 +0200Observation of a Field Induced Transition in the Vortex Solid of DyBa2Cu3O7/(Y1-xPrx)Ba2Cu3O7 Superlatticeshttps://archive-ouverte.unige.ch/unige:117880https://archive-ouverte.unige.ch/unige:117880We report on the observation of a change in the field dependence of the critical current density Jc of DyBa2Cu3O7/(Y0.45Pr0.55)Ba2Cu3O7 superlattices at a characteristic magnetic field H∗s. This change shows up as an abrupt transition when analyzing the current-voltage ( I−V) characteristics in the framework of the vortex glass and collective flux creep theories. This behavior can be traced back to a sudden reduction in the collective pinning energy Uc above H∗s, and may reflect a softening transition of the vortex lines in the vortex solid. H∗s is very similar to the characteristic field H∗l in the vortex liquid phase, which we interpreted to be due to entanglement.Tue, 21 May 2019 14:18:59 +0200Hot-carrier scattering in a metal: a ballistic-electron-emission microscopy investigation on PtSihttps://archive-ouverte.unige.ch/unige:117877https://archive-ouverte.unige.ch/unige:117877Ballistic-electron-emission microscopy (BEEM) has been used to study the PtSi/n-type Si(100) interface. Hot-electron transport has been investigated by measuring the ballistic-electron transmission as a function of position (BEEM imaging), energy (BEEM spectroscopy), and PtSi thickness (BEEM attenuation length). Hot-hole transport and electron-electron scattering have also been investigated as a function of these parameters. This study has been conducted on in situ fabricated PtSi/n-type Si(100) Schottky diodes in UHV with the silicide thickness ranging from 20 to 500 Å. The PtSi films were granular and the BEEM transmissivity was found to be homogeneous on individual grains but strongly varying from one grain to another. We attempt to compare the absolute BEEM current level with existing models and find its limiting value for small silicide thicknesses to be close to 1 depending on the model considered, indicating efficient transmission due to strong forward focusing of the electrons in the base or enhancement due to multiple scattering within the grains. BEEM current as a function of silicide thickness shows a change from a rapid to a slower decrease at about 150 Å. Reverse BEEM (RBEEM) attenuation lengths also show this qualitative behavior, but the attenuation with increasing PtSi thickness is distinctly weaker, indicating that BEEM and RBEEM intensities are differently influenced by the elastic and inelastic hot-carrier mean free paths. RBEEM spectra are found to be anomalous, indicating an anomalous distribution of the tunnel-injected hot holes in the base.Tue, 21 May 2019 14:11:54 +0200Properties of g→bb¯ at small opening angles in pp collisions with the ATLAS detector at √s = 13 TeVhttps://archive-ouverte.unige.ch/unige:116886https://archive-ouverte.unige.ch/unige:116886The fragmentation of high-energy gluons at small opening angles is largely unconstrained by present measurements. Gluon splitting to b-quark pairs is a unique probe into the properties of gluon fragmentation because identified b-tagged jets provide a proxy for the quark daughters of the initial gluon. In this study, key differential distributions related to the g→bb¯ process are measured using 33 fb−1 of s=13 TeV pp collision data recorded by the ATLAS experiment at the LHC in 2016. Jets constructed from charged-particle tracks, clustered with the anti-kt jet algorithm with radius parameter R=0.2, are used to probe angular scales below the R=0.4 jet radius. The observables are unfolded to particle level in order to facilitate direct comparisons with predictions from present and future simulations. Multiple significant differences are observed between the data and parton shower Monte Carlo predictions, providing input to improve these predictions of the main source of background events in analyses involving boosted Higgs bosons decaying into b-quarks.Thu, 02 May 2019 17:43:54 +0200