Vienna University of Technology

About: Vienna University of Technology is a education organization based out in Vienna, Austria. It is known for research contribution in the topics: Laser & Context (language use). The organization has 16723 authors who have published 49341 publications receiving 1302168 citations.

Observation of Rapid Exciton–Exciton Annihilation in Monolayer Molybdenum Disulfide

Abstract: Monolayer MoS2 is a direct-gap two-dimensional semiconductor that exhibits strong electron–hole interactions, leading to the formation of stable excitons and trions. Here we report the existence of efficient exciton–exciton annihilation, a four-body interaction, in this material. Exciton–exciton annihilation was identified experimentally in ultrafast transient absorption measurements through the emergence of a decay channel varying quadratically with exciton density. The rate of exciton–exciton annihilation was determined to be (4.3 ± 1.1) × 10–2 cm2/s at room temperature.

Pump-induced exceptional points in lasers.

Abstract: We demonstrate that the above-threshold behavior of a laser can be strongly affected by exceptional points which are induced by pumping the laser nonuniformly. At these singularities, the eigenstates of the non-Hermitian operator which describes the lasing modes coalesce. In their vicinity, the laser may turn off even when the overall pump power deposited in the system is increased. Such signatures of a pump-induced exceptional point can be experimentally probed with coupled ridge or microdisk lasers.

Experimental demonstration of a BDCZ quantum repeater node.

Abstract: At distances beyond about 100 km, quantum communication fails due to photon losses in the transmission channel. To overcome this problem, Briegel, Dur, Cirac and Zoller (BDCZ) introduced the concept of quantum repeaters, combining entanglement swapping and quantum memory to efficiently extend the achievable distances. Their implementation has proved challenging due to the difficulty of integrating a quantum memory. Zhen-ShengYuan et al. realize a building block of the BDCZ quantum repeater, demonstrating entanglement swapping with storage and retrieval of light from atomic quantum memories. Quantum communication is a method that offers efficient and secure ways for the exchange of information in a network. Large-scale quantum communication1,2,3,4 (of the order of 100 km) has been achieved; however, serious problems occur beyond this distance scale, mainly due to inevitable photon loss in the transmission channel. Quantum communication eventually fails5 when the probability of a dark count in the photon detectors becomes comparable to the probability that a photon is correctly detected. To overcome this problem, Briegel, Dur, Cirac and Zoller (BDCZ) introduced the concept of quantum repeaters6, combining entanglement swapping7 and quantum memory to efficiently extend the achievable distances. Although entanglement swapping has been experimentally demonstrated8, the implementation of BDCZ quantum repeaters has proved challenging owing to the difficulty of integrating a quantum memory. Here we realize entanglement swapping with storage and retrieval of light, a building block of the BDCZ quantum repeater. We follow a scheme9,10 that incorporates the strategy of BDCZ with atomic quantum memories11. Two atomic ensembles, each originally entangled with a single emitted photon, are projected into an entangled state by performing a joint Bell state measurement on the two single photons after they have passed through a 300-m fibre-based communication channel. The entanglement is stored in the atomic ensembles and later verified by converting the atomic excitations into photons. Our method is intrinsically phase insensitive and establishes the essential element needed to realize quantum repeaters with stationary atomic qubits as quantum memories and flying photonic qubits as quantum messengers.

COFI RANK - Maximum Margin Matrix Factorization for Collaborative Ranking

Abstract: In this paper, we consider collaborative filtering as a ranking problem. We present a method which uses Maximum Margin Matrix Factorization and optimizes ranking instead of rating. We employ structured output prediction to optimize directly for ranking scores. Experimental results show that our method gives very good ranking scores and scales well on collaborative filtering tasks.

Reaction of O2 with Subsurface Oxygen Vacancies on TiO2 Anatase (101)

Abstract: Oxygen (O2) adsorbed on metal oxides is important in catalytic oxidation reactions, chemical sensing, and photocatalysis. Strong adsorption requires transfer of negative charge from oxygen vacancies (V(O)s) or dopants, for example. With scanning tunneling microscopy, we observed, transformed, and, in conjunction with theory, identified the nature of O2 molecules on the (101) surface of anatase (titanium oxide, TiO2) doped with niobium. V(O)s reside exclusively in the bulk, but we pull them to the surface with a strongly negatively charged scanning tunneling microscope tip. O2 adsorbed as superoxo (O2(-)) at fivefold-coordinated Ti sites was transformed to peroxo (O2(2-)) and, via reaction with a VO, placed into an anion surface lattice site as an (O2)O species. This so-called bridging dimer also formed when O2 directly reacted with V(O)s at or below the surface.