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Search Results: 1 - 10 of 3551 matches for " Tobias Gaber "
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Semifluxon molecule under control
Andreas Dewes,Tobias Gaber,Dieter Koelle,Reinhold Kleiner,Edward Goldobin
Physics , 2008, DOI: 10.1103/PhysRevLett.101.247001
Abstract: Josephson junctions with a phase drop pi in the ground state allow to create vortices of supercurrent carrying only half of the magnetic flux quantum Phi_0~2.07*10^-15 Wb. Such semifluxons have two-fold degenerate ground states denoted up (with flux +Phi_0/2 and supercurrent circulating clockwise) and down (with flux -Phi_0/2 and supercurrent circulating counterclockwise). We investigate a molecule consisting of two coupled semifluxons in a 0-pi-0 long Josephson junction. The fluxes (polarities) of semifluxons are measured by two on-chip SQUIDs. By varying the dc bias current applied to the 0-pi-0 junction, we demonstrate controllable manipulation and switching between two states, up-down and down-up, of a semifluxon molecule. These results provide a major step towards employing semifluxons as bits or qubits for classical and quantum digital electronics.
Improving the performance of superconducting microwave resonators in magnetic fields
Daniel Bothner,Tobias Gaber,Matthias Kemmler,Dieter Koelle,Reinhold Kleiner
Physics , 2011, DOI: 10.1063/1.3560480
Abstract: The operation of superconducting coplanar waveguide cavities, as used for circuit quantum electrodynamics and kinetic inductance detectors, in perpendicular magnetic fields normally leads to a reduction of the device performance due to energy dissipating Abrikosov vortices. We experimentally investigate the vortex induced energy losses in such Nb resonators with different spatial distributions of micropatterned pinning sites (antidots) by transmission spectroscopy measurements at 4.2 K. In comparison to resonators without antidots we find a significant reduction of vortex induced losses and thus increased quality factors over a broad range of frequencies and applied powers in moderate fields.
Magnetic hysteresis effects in superconducting coplanar microwave resonators
Daniel Bothner,Tobias Gaber,Matthias Kemmler,Dieter Koelle,Reinhold Kleiner,Stefan Wünsch,Michael Siegel
Physics , 2012, DOI: 10.1103/PhysRevB.86.014517
Abstract: We performed transmission spectroscopy experiments on coplanar half wavelength niobium resonators at a temperature T=4.2 K. We observe not only a strong dependence of the quality factor Q and the resonance frequency f_res on an externally applied magnetic field but also on the magnetic history of our resonators, i.e. on the spatial distribution of trapped Abrikosov vortices in the device. We find these results to be valid for a broad range of frequencies and angles between the resonator plane and the magnetic field direction as well as for resonators with and without antidots near the edges of the center conductor and the ground planes. In a detailed analysis we show, that characteristic features of the experimental data can only be reproduced in calculations, if a highly inhomogeneous rf-current density and a flux density gradient with maxima at the edges of the superconductor is assumed. We furthermore demonstrate, that the hysteretic behaviour of the resonator properties can be used to considerably reduce the vortex induced losses and to fine-tune the resonance frequency by the proper way of cycling to a desired magnetic field.
All-fibre source of amplitude-squeezed light pulses
Markus Meissner,Christoph Marquardt,Joel Heersink,Tobias Gaber,André Wietfeld,Gerd Leuchs,Ulrik L. Andersen
Physics , 2004, DOI: 10.1088/1464-4266/6/8/005
Abstract: An all-fibre source of amplitude squeezed solitons utilizing the self-phase modulation in an asymmetric Sagnac interferometer is experimentally demonstrated. The asymmetry of the interferometer is passively controlled by an integrated fibre coupler, allowing for the optimisation of the noise reduction. We have carefully studied the dependence of the amplitude noise on the asymmetry and the power launched into the Sagnac interferometer. Qualitatively, we find good agreement between the experimental results, a semi-classical theory and earlier numerical calculations [Schmitt etl.al., PRL Vol. 81, p.2446, (1998)]. The stability and flexibility of this all-fibre source makes it particularly well suited to applications in quantum information science.
Boundary Control Problem of Infinite Order Distributed Hyperbolic Systems Involving Time Lags  [PDF]
Bahaa Gaber Mohamed
Intelligent Control and Automation (ICA) , 2012, DOI: 10.4236/ica.2012.33024
Abstract: Various optimal boundary control problems for linear infinite order distributed hyperbolic systems involving constant time lags are considered. Constraints on controls are imposed. Necessary and sufficient optimality conditions for the Neumann problem with the quadratic performance functional are derived.
Fiscal stimulations for improving the business environment in Republic of Macedonia
Stevan Gaber
Perspectives of Innovations, Economics and Business , 2009,
Abstract: In conditions when the national economy is hit hard with catastrophic economic consequences from financial crises, mutual coordinative approach between fiscal authorities and independent monetary institution, entrusted for macroeconomic stability, is particularly essential. This paper focuses on the situation, when there is not, at least temporary, constructive dialog between the two most important institutions in the country, and consequences are paid by enterprises and citizens.
Mythic Foundations: Engaging History for Architecture Education
Tammy Gaber
Archnet-IJAR : International Journal of Architectural Research , 2012,
Abstract:
The phase boundary of superconducting niobium thin films with antidot arrays fabricated with microsphere photolithography
Daniel Bothner,Conrad Clauss,Elisabeth Koroknay,Matthias Kemmler,Tobias Gaber,Michael Jetter,Marc Scheffler,Peter Michler,Martin Dressel,Dieter Koelle,Reinhold Kleiner
Physics , 2012, DOI: 10.1088/0953-2048/25/6/065020
Abstract: The experimental investigation of the $I_c(B)$--$T_c(B)$ phase boundary of superconducting niobium films with large area quasihexagonal hole arrays is reported. The hole arrays were patterned with microsphere photolithography. We investigate the perforated niobium films by means of electrical directed current transport measurements close to the transition temperature $T_c$ in perpendicularly applied magnetic fields. We find pronounced modulations of the critcal current with applied magnetic field, which we interpret as a consequence of commensurable states between the Abrikosov vortex lattice and the quasihexagonal pinning array. Furthermore, we observe Little-Parks oscillations in the critical temperature vs magnetic field.
Excited State Interaction of Laser Dyes and Silver Nanoparticles in Different Media  [PDF]
Yusif S. El-Sayed, Mohamad Gaber
Advances in Nanoparticles (ANP) , 2012, DOI: 10.4236/anp.2012.13008
Abstract: Quenching the fluorescence of the dyes 3-(4’-dimethylaminophenyl)-1-(1H-pyrrol-2-yl)prop-2-en-1-one (DMAPrP), 3- (4’-dimethylaminophenyl)-1-(2-furanyl)prop-2-en-1-one (DMAFP) and 3-(4’-dimethylaminophenyl)-1-(2-thienyl)prop- 2-en-1-one (DMATP) has been investigated in the presence of silver cation and silver nanoparticles in different media. The results of the quenching experiments were analyzed using Stern-Volmer equation. Quenching the fluorescence of the dyes decreased with increasing medium viscosity. The Stern-Volmer constant (KSV) values in the absence and presence of ethylene glycol show that the quenching efficiencies decrease as the medium viscosity increases indicating that the quenching process is a diffusion-controlled process, and this is consistent with a dynamic-type quenching.
Boundary Control for 2 × 2 Elliptic Systems with Conjugation Conditions  [PDF]
Ahlam Hasan Qamlo, Bahaa Gaber Mohammed
Intelligent Control and Automation (ICA) , 2013, DOI: 10.4236/ica.2013.43032
Abstract:

In this paper, we consider 2 × 2 non-cooperative elliptic system involving Laplace operator defined on bounded, continuous and strictly Lipschitz domain of Rn. First we prove the existence and uniqueness for the state of the system under conjugation conditions; then we discuss the existence of the optimal control of boundary type with Neumann conditions, and we find the set of equations and inequalities that characterize it.

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