1,721,019 research outputs found
Minor embedding with Stuart-Landau oscillator networks
No full textWe theoretically implement a strategy from quantum computation architectures to simulate Stuart-Landau oscillator dynamics in all-to-all connected networks, also referred to as complete graphs. The technique builds upon the triad structure minor embedding which expands dense graphs of interconnected elements into sparse ones which can potentially be realized in future onchip solid state technologies with tunable edge weights. As a case study, we reveal that the minor embedding procedure allows simulating the XY model on complete graphs, thus bypassing a severe geometric constraint
Plasmon enhanced optical tweezers with gold-coated black silicon
No full textPlasmonic optical tweezers are a ubiquitous tool for the precise manipulation of nanoparticles and biomolecules at low photon flux, while femtosecond-laser optical tweezers can probe the nonlinear optical properties of the trapped species with applications in biological diagnostics. In order to adopt plasmonic optical tweezers in real-world applications, it is essential to develop large-scale fabrication processes without compromising the trapping efficiency. Here, we develop a novel platform for continuous wave (CW) and femtosecond plasmonic optical tweezers, based on gold-coated black silicon. In contrast with traditional lithographic methods, the fabrication method relies on simple, single-step, maskless tabletop laser processing of silicon in water that facilitates scalability. Gold-coated black silicon supports repeatable trapping efficiencies comparable to the highest ones reported to date. From a more fundamental aspect, a plasmon-mediated efficiency enhancement is a resonant effect, and therefore, dependent on the wavelength of the trapping beam. Surprisingly, a wavelength characterization of plasmon-enhanced trapping efficiencies has evaded the literature. Here, we exploit the repeatability of the recorded trapping efficiency, offered by the gold-coated black silicon platform, and perform a wavelength-dependent characterization of the trapping process, revealing the resonant character of the trapping efficiency maxima. Gold-coated black silicon is a promising platform for large-scale parallel trapping applications that will broaden the range of optical manipulation in nanoengineering, biology, and the study of collective biophotonic effects
Photocurrent enhancement in hybrid nanocrystal quantum-dot p-i-n photovoltaic devices
No full textWe fabricate a hybrid nanocrystal quantum-dot patterned p-i-n structure that utilizes nonradiative energy transfer from highly absorbing colloidal nanocrystal quantum dots to a patterned semiconductor slab to demonstrate a sixfold increase of the photocurrent conversion efficiency compared to the bare p-i-n semiconductor device.<br/
Nonradiative exciton energy transfer in hybrid organic-inorganic heterostructures
No full textNonradiative energy transfer from a GaAs quantum well to a thin overlayer of an infrared organic semiconductor dye is unambiguously demonstrated. The dynamics of exciton transfer are studied in the time domain by using pump-probe spectroscopy at the donor site and fluorescence spectroscopy at the acceptor site. The effect is observed as simultaneous increase in the population decay rate at the donor and of the rise time of optical emission at the acceptor sites. The hybrid configuration under investigation provides an alternative nonradiative, noncontact pumping route to electrical carrier injection that overcomes the losses imposed by the associated low carrier mobility of organic emitters
Nonlinear birefringence and time-resolved Kerr measurement of spin lifetimes in (110) GaAs/AlyGa1-yAs quantum wells
No full textWe report a study of the nonlinear birefringence in undoped (110)-oriented GaAs/AlGaAs quantum wells using time-resolved pump-probe Kerr spectroscopy. Due to the optical anisotropy of the (110) quantum well plane, photoexcited carriers can give rise to a nonlinear birefringence and so cause probe polarization rotation independent of the pump polarization, i.e., independent of spin orientation. We develop a methodology for accurate determination of electron-spin lifetimes using the Kerr technique which takes account of this phenomenon and present room-temperature measurements of wavelength and power density dependence of the spin-relaxation rate.<br/
T:sapphire channel waveguide lasers produced by femtosecond and picosecond laser writing
No full textUltra-short pulse laser writing is a widely adopted method for rapid prototyping of channel waveguide lasers and amplifiers in the bulk of different types of transparent glasses, crystals and ceramic materials [1, 2]. The writing process in laser crystals relies on engineering either depressed-cladding structures or two parallel tracks to confine the mode in the spacing in-between, by stress-induced increases in the refractive index. Ti:sapphire (a-Al2O3:Ti3+) with its broad emission bandwidth (650-1100 nm) is a benchmark solid-state gain medium for ultrashort laser pulse generation and broadly tuneable lasers. Here, we report on the continuous wave (cw) laser operation of Ti:sapphire channel waveguides fabricated by fs- and picosecond (ps) laser writing
Lotka-Volterra population dynamics in coherent and tunable oscillators of trapped polariton condensates
No full textWe demonstrate a regime in which matter-wave condensates of exciton-polaritons trapped in an elliptically shaped two-dimensional potential appear as a coherent mixture of ground and first-excited state of the quantum harmonic oscillator. This system resembles an optically controllable two-level system and produces near terahertz harmonic oscillations of the condensate’s center of mass along the major axis of the elliptical trapping potential. The population ratio between the two trap levels is tunable through the excitation laser power and is shown to follow Lotka-Volterra dynamics. Furthermore, we demonstrate coherence formation between two spatially displaced trapped condensate oscillators - the polaritonic analogue of Huygen’s clock synchronization for coupled condensate oscillators
Polarization rotation in parametric scattering of polaritons in semiconductor microcavities
No full textPolarization of light emitted by a semiconductor microcavity in the regime of a resonant parametric scattering of the exciton polaritons shows extremely strong and unusual dependence on the polarization of pumping light. This dependence is interpreted here using the pseudospin model and in the framework of a quasiclassical formalism where the parametric scattering is described as resonant four-wave mixing. We show that the optically induced splitting of the exciton-polariton eigenstate, both in linear and circular polarizations, is responsible for the observed polarization effects. The splitting in circular polarizations, achieving 0.5 meV, has been detected experimentally, while the splitting in linear polarizations, which is much weaker, only manifests itself in the pseudospin dynamics of the exciton polaritons
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