| 1. |
- Morrison, S, et al.
(författare)
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Physical replicas and the Bose glass in cold atomic gases
- 2008
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 10:7
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Tidskriftsartikel (refereegranskat)abstract
- We study cold atomic gases in a disorder potential and analyse the correlations between different systems subjected to the same disorder landscape. Such independent copies with the same disorder landscape are known as replicas. While, in general, these are not accessible experimentally in condensed matter systems, they can be realized using standard tools for controlling cold atomic gases in an optical lattice. Of special interest is the overlap function which represents a natural order parameter for disordered systems and is a correlation function between the atoms of two independent replicas with the same disorder. We demonstrate an efficient measurement scheme for the determination of this disorder-induced correlation function. As an application, we focus on the disordered Bose–Hubbard model and determine the overlap function within the perturbation theory and a numerical analysis. We find that the measurement of the overlap function allows for the identification of the Bose-glass phase in certain parameter regimes.
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| 2. |
- Alegret, Joan, 1977, et al.
(författare)
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Green's tensor calculations of plasmon resonances of single holes and hole pairs in thin gold films
- 2008
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Ingår i: New Journal of Physics. - Bristol, UK : IOP Publishing. - 1367-2630. ; 10, s. 13-
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Tidskriftsartikel (refereegranskat)abstract
- We present numerical calculations of the plasmon properties of single-hole and hole-pair structures in optically thin gold films obtained with the Green's tensor formalism for stratified media. The method can be used to obtain the optical properties of a given hole system, without problems associated with the truncation of the infinite metal film. The calculations are compared with previously published experimental data and an excellent agreement is found. In particular, the calculations are shown to reproduce the evolution of the hole plasmon resonance spectrum as a function of hole diameter, film thickness and hole separation.
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| 3. |
- Foerster, Heidi, et al.
(författare)
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Current-voltage correlations in interferometers
- 2007
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- We investigate correlations of current at contacts and voltage fluctuations at voltage probes coupled to interferometers. The results are compared with correlations of current and occupation number fluctuations at dephasing probes. We use a quantum Langevin approach for the average quantities and their fluctuations. For higher order correlations we develop a stochastic path integral approach and find the generating functions of voltage or occupation number fluctuations. We also derive a generating function for the joint distribution of voltage or occupation number at the probe and current fluctuations at a terminal of a conductor. For energy independent scattering we found earlier that the generating function of current cumulants in interferometers with a one-channel dephasing or voltage probe are identical. Nevertheless, the distribution function for voltage and the distribution function for occupation number fluctuations differ, the latter being broader than that of the former in all examples considered here.
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| 4. |
- Mansten, Erik, et al.
(författare)
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Spectral shaping of attosecond pulses using two-colour laser fields
- 2008
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- We use a strong two-colour laser field composed of the fundamental (800 nm) and the second harmonic (400 nm) of an infrared (IR) laser field to generate attosecond pulses with controlled spectral and temporal properties. With a second-harmonic intensity equal to 15% of the IR intensity the second-harmonic field is strong enough to significantly alter and control the electron trajectories in the generation process. This enables us to tune the central photon energy of the attosecond pulses by changing the phase difference between the IR and the second-harmonic fields. In the time domain the radiation is emitted as a sequence of pulses separated by a full IR cycle. We also perform calculations showing that the effect of even stronger second-harmonic fields leads to an extended tunable range under conditions that are experimentally feasible.
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| 5. |
- Reimann, Stephanie, et al.
(författare)
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Rotating quantum liquids crystallize
- 2006
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Small crystallites form when finite quantal systems are set highly rotating. This crystallization is independent of the statistics of the particles, and occurs for both trapped bosons and fermions. The spin degree of freedom does not change the tendency for localization. In a highly rotating state, the strongly correlated bosonic and fermionic systems approach to that of classical particles.
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| 6. |
- Stierle, A., et al.
(författare)
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Real time observation of ultrathin epitaxial oxide growth during alloy oxidation
- 2007
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 9, s. 331-331
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the thermal oxidation of the intermetallic alloy CoGa in situ, in real time on the atomic scale, during the growth of an ultrathin, epitaxial Ga oxide layer. On the basis of an extended set of surface x-ray diffraction data, density functional theory calculations and core level spectroscopy data, we find that the oxide film consists of an oxygen ion double layer, which contains the basic building block of bulk beta- Ga2O3. The oxide formation takes place via the nucleation of two- dimensional, anisotropic oxide islands which laterally grow and coalesce. A dramatic increase of the oxide island size is observed for low O-2 pressures in the 10(-8) mbar regime, which we interpret as the onset of a step flow like growth mode. This allows us to conclude that thermal oxidation can be considered as a hetero- epitaxial growth process, that follows similar atomistic growth principles to molecular beam epitaxy. As a consequence, the structural perfection of the oxide layer can be tailored by the appropriate choice of oxygen pressure and temperature.
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| 7. |
- Amann, M. C., et al.
(författare)
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Focus on advanced semiconductor heterostructures for optoelectronics
- 2009
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 11, s. 125012 artno-
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Tidskriftsartikel (refereegranskat)abstract
- Semiconductor heterostructures are the basic materials underlying optoelectronic devices, particularly lasers and light-emitting diodes (LEDs). Made from various III-V-, II-VI-, SiGe- and other compound semiconductors, modern semiconductor devices are available for the generation, detection and modulation of light covering the entire ultra-violet to far-infrared spectral region. Recent approaches that introduced multilayer heterostructures tailored on the lower nanometre scale made possible artificial semiconductors with new properties, such as extended wavelength coverage, that enabled new applications. Together with ongoing progress on wide-gap semiconductors, the optical wavelengths accessible by semiconductor devices are steadily expanding towards the short-wavelength ultra-violet regime, as well as further into the far-infrared and terahertz spectral regions. It is the aim of this focus issue to present cutting-edge research topics on the most recent optoelectronic material and device developments in this field using advanced semiconductor heterostructures.
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| 8. |
- Axelsson, S., et al.
(författare)
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Theoretical and experimental investigations of three-terminal carbon nanotube nanorelays
- 2005
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Ingår i: New J. Phys. - : IOP Publishing. - 1367-2630. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- We present theoretical and experimental investigations of three-terminal nanoelectromechanical relays based on suspended carbon nanotubes. A charge is induced in the nanotube by applying a voltage to an underlying gate electrode thus inducing the nanotube to bend and make contact with a drain electrode. Such devices have potential applications as fast switches, logic devices, memory elements and pulse generators. We describe two modes of operation: a contact mode where the nanotube makes physical contact with the drain electrode and a non-contact mode where electrical contact between the nanotube and the drain electrode is made via a field emission current.
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| 9. |
- Bishop, Lev S., et al.
(författare)
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Proposal for generating and detecting multi-qubit GHZ states in circuit QED
- 2009
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 11, s. 073040-
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Tidskriftsartikel (refereegranskat)abstract
- We propose methods for the preparation and entanglement detectionof multi-qubit Greenberger–Horne–Zeilinger (GHZ) states in circuit quantumelectrodynamics. Using quantum trajectory simulations appropriate for thesituation of a weak continuous measurement, we show that the joint dispersivereadout of several qubits can be utilized for the probabilistic production ofhigh-fidelity GHZ states. When employing a nonlinear filter on the recordedhomodyne signal, the selected states are found to exhibit values of theBell–Mermin operator exceeding 2 under realistic conditions. We discuss thepotential of the dispersive readout to demonstrate a violation of the Merminbound, and present a measurement scheme avoiding the necessity for fulldetector tomography.
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| 10. |
- Cremon, Jonas, et al.
(författare)
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Rotational properties of a mixture of two Bose gases
- 2008
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- A rotating, two-component Bose-Einstein condensate is shown to exhibit vortices of multiple quantization, which are possible due to the interatomic interactions between the two species. Also, persistent currents are absent in this system. Finally, the order parameter has a very simple structure for a range of angular momenta.
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