Program winter term 2014/2015
Physics Colloquium
| Date | Speaker | Title |
|---|---|---|
| 12/01/2015 | Prof. Dr. Franz von Feilitzsch (TU Munich) | Results of the Borexino experiment and perspectives of low energy neutrino astronomy |
| 08/12/2014 | Prof. Atac Imamoglu (ETH Zurich) | Cavity quantum electrodynamics with two-dimensional electron systems |
| 24/11/2014 | Prof. Susana Huelga (Ulm University) | Vibrations, Quanta and Biology |
| 10/11/2014 | Dr. Lieven Vandersypen (Delft University of Technology) | A silicon quantum computer |
| 27/10/2014 | Prof. Gene Mele (University of Pennsylvania USA, Loughborough University UK) | The Winding Road to Topological Insulators |
| 13/10/2014 | Klaus Scherer (Ruhr-Universität Bochum) | The Heliosphere An astrophysical laboratory for plasma physics and particle acceleration |
Monday, January 12, 2014, 4:15pm
Prof. Dr. Franz von Feilitzsch (TU Munich)
Results of the Borexino experiment and perspectives of low energy neutrino astronomys
Inviting Host: Wolfgang Wallraff
Abstract:
The "Borexino" experiment is a 300 m3 liquid scintillator detector
located in the Gran Sasso laboratory of the INFN, 1000 m underground
and 150 km from Rome in the Apprutzen mountains. The primary aim of the
experiment is the measurement of the solar neutrino spectrum down to
low energies, in particular the measurement of the mono-energetic
neutrinos from Be7 e-capture in the center of the sun. Recently, it
succeeded in addition to measure neutrinos from the dominant solar
pp-fusion at very low energies, which completes the measurement of the
full solar neutrino spectrum.
The impact of these results for neutrino oscillation parameters, solar
physics and further scientific goals like the measurement of neutrinos
emitted from the interior of the earth and the search for sterile
neutrinos are discussed together with possible future developments of
low energy neutrino astronomy.
Monday, December 08, 2014, 4:14pm
Prof. Atac Imamoglu (ETH Zurich)
Inviting host: Barbara Terhal
Cavity quantum electrodynamics with two-dimensional electron systems
Abstract:
Reversible coupling of excitons and photons in intrinsic semiconductor
quantum wells embedded inside a microcavity has been used to study
non-equilibrium condensation and superfluidity of cavity-
polaritons. The attempts to use this system to observe polariton
blockade on the other hand, has been hindered by the relatively weak
electron-exchange dominated interaction that scales linearly with the
exciton Bohr radius. I will present experiments on a high-mobility
two-dimensional electron gas (2DEG) simultaneously exhibiting strongly
correlated phases and non-perturbative coupling to a microcavity
mode. Tuning the cavity into resonance with the electron gas when
magnetic field Bz = 0 allows us to demonstrate a new dynamic regime of
Fermi-edge physics where many-body excitations are delocalized trion
Fermi-edge polaritons. With Bz != 0, the cavity-polariton excitations
show unique signatures of both integer and fractional quantum Hall
states. The system is potentially of interest for realizing strongly
correlated photonic systems since it may be possible to exploit strong
electron density dependence of 2DEG-polariton splitting, or
equivalently the trion Bohr radius, to enhance polariton-polariton
interactions.
Monday, November 24, 2014, 4:15pm
Prof. Susana Huelga (Ulm University)
Inviting host: Prof. David di Vincenzo
Vibrations, Quanta and Biology
Abstract:
Quantum biology is an emerging field of research that concerns itself
with the experimental and theoretical exploration of non-trivial
quantum phenomena in biological systems.
At the heart of these investigations are the recent observations of
beating signals in the excitation energy transfer dynamics of
photosynthetic complexes, which have been interpreted as evidence for
sustained coherent behaviour. The microscopic origin of these
long-lived oscillations, however, remains to be fully uncovered. We
will show that the coupling of excitonic and vibrational motion in
molecular aggregates can provide efficient mechanisms leading to
persistent excitonic coherence [1-3]. The non-trivial spectral
structures of the environmental fluctuations and particularly discrete
vibrational modes can lead to the generation and sustenance of both
oscillatory energy transport and electronic coherence on timescales
that are comparable to excitation energy transfer [4]. We discuss the
spectral properties of the model in order to test the relation of the
proposed mechanism to actual experimental observations of oscillatory
behaviour using 2D photon echo techniques [5]. Recent experimental
results using J-aggregates also fit nicely within this framework and
corroborate the fundamental importance of the interplay of electronic
and vibrational degrees of freedom in the dynamics of light harvesting
aggregates.
[1] M. del Rey, A. W. Chin, S. F. Huelga, M. B. Plenio, J. Phys. Chem. Lett. 4, 903 (2013)
[2] F. Caycedo-Soler, A. W. Chin, J. Almeida, S. F. Huelga, M. B. Plenio, J. Chem. Phys. 136, 155102 (2012)
[3] A. W. Chin, J. Prior, R. Rosenbach, F. Caycedo-Soler, S. F. Huelga, M. B. Plenio, Nature Physics 9, 113 (2013)
[4] J. Prior, A. W. Chin, S. F. Huelga, M .B. Plenio, Phys. Rev. Lett. 105, 050404 (2010)
[5] M. B. Plenio, J. Almeida, S. F. Huelga, J. Chem. Phys. 139, 235102 (2013)
Monday, November 10, 2014, 4:15pm
Dr. Lieven Vandersypen (Delft University of Technology)
Inviting host: Prof. Hendrik Bluhm
Abstract:
A hundred years after its discovery, the predictions of quantum theory
remain highly fascinating and puzzling. Going beyond the surprise, we
ask ourselves how quantum superposition and entanglement can be used
to accomplish tasks that are otherwise impossible. A prime example is
the quantum computer, which offers the promise of solving important
problems that are otherwise out of reach. In the past decade, we have
learned to initialise, manipulate, and read out individual electron
spins trapped in small arrays of semiconductor quantum dots, thus
creating small quantum registers. Today, a central question is what it
takes to scale up to very large numbers of quantum bits. Increasingly,
silicon provides part of the answer.
Monday, October 27, 2014, 4:15pm
Prof. Gene Mele (University of Pennsylvania USA, Loughborough University UK)
The Winding Road to Topological Insulators
Abstract:
This talk surveys the classification of electric states of matter
with a focus on the unique properties of topological insulators and
their discovery from a careful consideration of the low energy
properties of single layer graphene. The topological band theoretic
classification of insulating states in two and three dimensions and
experimental realizations are briefly discussed.
Monday, October 13, 2014, 4:15pm
Klaus Scherer (Ruhr-Universität Bochum)
Inviting host: Prof. Christopher Wiebusch
The Heliosphere An astrophysical laboratory for plasma physics and particle acceleration
Abstract:
The interaction of the supersonic solar/stellar wind with the
interstellar medium generates shock structures and related hydrodynamic
features like Mach disks. Including magnetic fields and neutrals in the
fluid changes the hydrodynamical structures and leads to new
phenomena. These large scale structures affect the transport and
acceleration of energetic particles like cosmic rays.
Some of the contemporary transport theories and large scale models will
be presented as well as the associated spacecraft observations.