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Calendar of Physics Talks Vienna
| Finite endpoint momentum strings and applications to energy loss |
| Speaker: | Andrej Ficnar (Columbia University) |
| Abstract: | I will argue that classical strings, both bosonic and supersymmetric, can have finite energy and momentum at their endpoints. I will also show that, in a general curved background, the string endpoints must propagate along null geodesics as long as their energy remains finite. Finite endpoint momentum allows strings with a fixed energy to travel a greater distance in an AdS5-Schwarzschild background than has been possible for classical solutions considered previously. I will also review the relevance to heavy ion phenomenology of the dependence of this distance on energy and propose a scheme for determining the instantaneous rate of energy loss. |
| Date: | Tue, 07.01.2014 |
| Time: | 12:30 |
| Duration: | 60 min |
| Location: | Vienna University of Technology, Wiedner Hauptstr. 8-10, yellow area, 10th floor, seminar room E136 |
| Contact: | Iva Lovrekovic, Albert Georg Passegger - www.univie.ac.at/lunch-seminar |
| Passivity, thermal equilibrium states and correlation inequalities |
| Speaker: | Albert Georg Passegger (Univ.Wien) |
| Abstract: | im Rahmen des Seminars für Mathematische Physik |
| Date: | Tue, 07.01.2014 |
| Time: | 14:15 |
| Duration: | 60 min |
| Location: | Fakultät für Physik, Erwin-Schrödinger-Hörsaal, Boltzmanngasse 5, 5. Stock |
| Contact: | J. Yngvason |
| Gamma-ray bursts as the sources of the ultrahigh-energy cosmic rays? |
| Speaker: | Walter Winter (Univ. Würzburg) |
| Abstract: | im Rahmen des Teilchenphysikseminars |
| Date: | Thu, 09.01.2014 |
| Time: | 14:15 |
| Duration: | 60 min |
| Location: | Fakultät für Physik, Erwin-Schrödinger-Hörsaal, Boltzmanngasse 5, 5. Stock |
| Contact: | W. Grimus, H. Neufeld |
| Globally regular instability of AdS_3 |
| Speaker: | Joanna Jalmuzna (Univ. Krakau) |
| Abstract: | im Rahmen des Literaturseminars für Gravitation |
| Date: | Thu, 09.01.2014 |
| Time: | 14:15 |
| Duration: | 60 min |
| Location: | Arbeitsgruppe Gravitation, Währinger Straße 17, Semiarraum A. 2. Stock |
| Contact: | H. Rumpf |
| Heisenberg-type error-disturbance trade-off for qubits |
| Speaker: | Paul BUSCH (Department of Mathematics, U York, UK) |
| Abstract: | Reports on experiments recently performed in Vienna [Erhard et al, Nature Phys. 8, 185 (2012)] and Toronto [Rozema et al, Phys. Rev. Lett. 109, 100404 (2012)] include claims of a violation of Heisenberg’s error-disturbance relation. In contrast, we have presented and proven a Heisenberg-type relation for joint measurements of position and momentum [Phys. Rev. Lett. 111, 160405 (2013)]. To resolve the apparent conflict, we formulate here a new general trade-off relation for errors in qubit measurements, using the same concepts as we did in the position-momentum case. We show that the combined errors in an approximate joint measurement of a pair of ±1-valued observables A;B are tightly bounded from below by a quantity that measures the degree of incompatibility of A and B. We consider the claim of a violation of Heisenberg problematic as it is based on measures of error and disturbance that are of limited applicability. These measures are used in an inequality that was formulated by Ozawa as a correction of a wrong inequality - one which is incorrectly attributed to Heisenberg. We will see that Ozawa’s quantities overestimate the errors and are themselves found to obey a trade-off relation of the Heisenberg form in the qubit case. Finally we show how the experiments mentioned may directly be used to test our error inequality.
The talk is based on two recent papers by PB, P Lahti and R Werner:
Heisenberg Uncertainty for Qubit Measurements;
Noise Operators and Measures of RMS Error and Disturbance in Quantum Mechanics.
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| Date: | Fri, 10.01.2014 |
| Time: | 11:00 |
| Location: | Atominstitut Hörsaal, Stadionallee 2, 1020 Wien |
| Contact: | H. Abele |
| Nanophotonics of optical fibres |
| Speaker: | Misha SUMETSKY (Ashton Institute of Photonic Technologies, Ashton University, UK) |
| Abstract: | Nanoscale effects in highly transparent dielectric photonic structures fabricated from optical fibres are reviewed. In contrast to those in plasmonics, these structures do not contain metal particles, wires, or films with nanoscale dimensions. Nevertheless, a nanoscale perturbation of the fibre radius can significantly alter their performance. In the first part of this presentation, propagation of light in thin optical fibres (microfibers) having the radius of the order of 100 nanometres to 1 micron is considered. The fundamental mode propagating along a microfiber has an evanescent field which may be strongly expanded into the external area. Then, the cross-sectional dimensions and structure of the mode and transmission losses strongly vary with nanoscale variations of the microfiber radius. In the second part of the presentation, slow propagation of whispering gallery modes in fibres having the radius of the order of 10 to 100 microns is considered. The propagation of these modes along the fibre axis is so slow that they can be governed by extremely small nanoscale changes of the optical fibre radius. This phenomenon is exploited in SNAP (Surface Nanoscale Axial Photonics), a new platform for fabrication of miniature super-low-loss photonic integrated circuits with unprecedented sub-angstrom precision. The SNAP theory and applications are overviewed. |
| Date: | Fri, 10.01.2014 |
| Time: | 15:30 |
| Location: | Atominstitut Hörsaal, Stadionallee 2, 1020 Wien |
| Contact: | A. Rauschenbeutel |
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