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Spring Term |
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04 Jun 2012 |
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Professor Shmuel Fishman,
Department of Physics, Technion |
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Monday 12:00 |
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TRANSPORT IN
POTENTIALS RANDOM IN SPACE AND TIME: FROM |
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Room 308/8 |
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ANDERSON LOCALIZATION
TO SUPERBALLISTIC MOTION |
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Transport in presence of potentials that are random both in space
and time will be discussed. As a result of the time dependence
Anderson localization is destroyed resulting in transport that may
be superballistic. Universality classes of this transport are
identified. Most of the results are analytical. The approximations
are tested numerically. The results are relevant for experiments in
optics and in atom optics.
Get the flier... |
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28 May 2012 |
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Dr Rodislav Driben, School of
Physics and Astronomy, Tel Aviv University |
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Monday 12:00 |
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ACCELERATED ROGUE
WAVES GENERATED BY SOLITON FUSION |
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Room 308/8 |
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IN PHOTONIC CRYSTAL
FIBERS |
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Soliton fusion is a fascinating mechanism that was observed in
various fields of physics. Here we report the numerical observation
of soliton fusion in a complex process of interactions between
Raman-shifted solitons and dispersive waves at the advanced stage of
supercontinuum generation in photonic crystal fibers. Solitonic and
non-solitonic products of initial fission of the injected
higher–order soliton continue to propagate along the photonic
crystal fiber with different frequencies exhibiting multiple
interactions and generating light with a broad spectrum. It was
demonstrated that dispersive waves radiated from one soliton may
accelerate neighboring soliton causing further collision between
them. In most cases the nature of such collisions is quasi-elastic,
however soliton fusion and steering is also observed, depending on
relative velocity and energy of solitons. In our case of solitons
fusion both components combine into single robust structure
propagating with the enhanced energy and acceleration. After the
propagation length of 460 mm the output fusion product has
experienced significant temporal shift, well-preserving its robust
shape and intensity of about twice of the parental solitons. In the
spectral domain this processes result in development of a new
significant band at the long wavelength side of the spectrum. As
mentioned above, conditions for the fusion are very delicate and
assuming small random noise in input, the event becomes a rare one.
Obviously fused accelerated soliton is a very attractive candidate
for optical analog of rogue waves.
Get the flier... |
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23 May 2012 |
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Dr Hamutal Bary-Soroker,
Department of Physics, Ben Gurion University |
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Wed 12:00 |
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Room 308/8 |
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PAIR-BREAKING
EFFECT ON PERSISTENT CURRENTS |
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Consider a mesoscopic ring threaded by a static magnetic flux. This
is a realization of the Aharonov-Bohm effect: due to the flux an
equilibrium current flows in the ring. This current does not decay
in time, and hence is called persistent current. In 1990 persistent
currents of normal metallic rings were first observed. Surprisingly,
the amplitude of the observed currents is substantially larger than
the one expected theoretically. This poses a long standing puzzle.
In this talk I will present a possible solution to this puzzle.
Get the flier... |
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21 May 2012 |
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Professor Vladimir Zelevinsky,
Michigan State University |
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Monday 12:00 |
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Room 308/8 |
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ATOMIC NUCLEUS AND
MANY-BODY QUANTUM CHAOS |
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Many-body quantum chaos is a general phenomenon in many-body quantum
systems consisting of interacting constituents. When excitation
energy and level density grow, the stationary states of the system
are exceedingly complicated superpositions of simple modes. At this
stage quantum dynamics approaches the limits of random matrix
theory. It will be shown that many-body quantum chaos has its own
regularities which can serve as a diverse powerful tool for (i)
extracting fine structure levels invisible in experiments with poor
resolution, (ii) creating new computational methods and even (iii)
formulating a new approach to justification of statistical
mechanics.
Get the flier... |
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14 May 2012 |
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Dr Igor Kuzmenko,
Department of Physics, Ben Gurion University |
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Monday 12:00 |
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Room 308/8 |
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KONDO TUNNELING
INTO A QUANTUM SPIN HALL INSULATOR |
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We consider Kondo tunneling through a junction composed of a normal
metal, quantum dot and 2D topological insulator in a quantum spin
Hall state. The Kondo effect can be probed by measuring the dc
current induced by a dc bias voltage applied across the dot.
Coupling between the helical states on the opposite sides of the
topological insulator opens a gap in the edge states spectrum, which
naturally affects the tunneling conductance. Screening of the
magnetic impurity becomes less effective and that affects electron
transport through the junction. Specifically, when edge state
coupling is strong enough, the tunneling differential conductance
develops a dip at zero temperature instead of the standard zero bias
Kondo peak.
Get the flier... |
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07 May 2012 |
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Dr Oded Kenneth, School of
Physics and Astronomy, Tel Aviv University |
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Monday 12:00 |
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Room 308/8 |
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LOW REYNOLDS
SWIMMERS |
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A swimmer is an object (usually immersed in fluid) which manages to
translate itself in space by cyclically deforming its shape with no
need for externally exerted net force. At the low Reynolds number
regime, swimming becomes geometric (in a sense to be explained). The
talk will concentrate mostly on the general framework for describing
and calculating such swimming. I will also briefly show a few
examples of swimmers I have worked on.
Get the flier... |
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02 May 2012 |
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Dr Alla Zak, Department of
Materials and Interfaces, Weizmann Institute |
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Wed 12:00 |
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INORGANIC
FULLERENE-LIKE NANOPARTICLES AND NANOTUBES, |
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Room 308/8 |
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THEIR SYNTHESIS AND
APPLICATIONS |
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The industrial development of the 21st century requires new smart
and miniaturized devices, strong and light materials, materials with
wide variety of new properties. Nanotechnology based on
nanocompounds comes to address this need. Inorganic fullerene-like
(IF) nanoparticles and inorganic nanotubes (INT) from MoS_2 and WS_2
were discovered in 1992 in the laboratory of Prof. Tenne, Weizmann
Institute of Science. During last two decades it was shown that not
only carbon, WS_2 and MoS_2, but whole family of transition metal
dichalcogenides like SnS_2, TaS_2, TiS_2, as well as numerous
metal-oxide and metal-halide with layered structure could form
nanoparticles with spherical and tubular morphology when prepared
under appropriate synthetic conditions. Careful investigation of the
IF- and INT-WS_2 growth mechanism resulted in the synthesis of a
pure phase and paved the way for the scaled up production. Large
amounts of nanopowders allow extensive investigation of their
intrinsic properties and possible applications. Many studies were
carried out aiming at studying catalytic effects of these
nanoparticles, their optical and electrical behavior, and
influencing polymers’ properties by adding tiny amounts of these
nanoparticles. Promising results were obtained with respect to the
mechanical, thermal, and tribological behavior of polymer
nanocomposites. Initial results were obtained for electrical and
catalytic applications. Synthesis of nanoparticles from MoS_2 or
from other transition dichalcogenides needs additional efforts to
become scalable, which should result in new materials with advanced
properties for new applications.
Get the flier... |
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30 Apr 2012 |
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Professor Nir Davidson,
Department of Physics of Complex Systems, Weizmann Institute |
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Monday 12:00 |
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LONG COHERENCE TIMES
WITH DENSE ULTRA-COLD ATOMIC |
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Room 308/8 |
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ENSEMBLES |
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Ultra cold atomic ensembles have potential applications in quantum
information science. Owing to collective enhancement, high density
ensembles increase the overall efficiency of quantum operations, but
at the same time also increase the atomic collision rate and
markedly change the time dynamics of a stored coherence. We study
theoretically and experimentally the coherent dynamics of cold atoms
under these conditions. A closed form expression for the spectral
line shape is derived for discrete fluctuations in terms of the bare
spectrum and the Poisson rate constant of collisions, which deviates
from the canonical stochastic theory of Kubo. We measure a
prolongation of the coherence times of optically trapped rubidium
atoms as their density increases, a phenomenon we call collisional
narrowing in analog to the well known motional narrowing effect in
NMR. We explain under what circumstances collisional narrowing can
be transformed into collisional broadening. On account of
collisions, conventional echo techniques fail to suppress this
dephasing, and multi-pulse dynamical decoupling sequences
are required. We present experiments demonstrating a 20-fold
increase of the coherence time when a sequence with more than 200
echo pulses is applied. We perform quantum process tomography and
demonstrate that using the decoupling scheme a dense ensemble with
an optical depth of >200 can be used as an atomic memory with
coherence times exceeding 3 sec. Further optimization requires
utilizing specific features of the collisional bath, which we
measure directly. Finally, the spectral system we study can be
mapped on a real space anomalous diffusion problem that we also
investigate.
Get the flier... |
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23 Apr 2012 |
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Professor Sven Gnutzmann,
University of Nottingham, United Kingdom |
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Monday 12:00 |
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Room 308/8 |
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TOPOLOGICAL
RESONANCES AND NONLINEAR WAVES IN METRIC GRAPHS |
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We consider wave scattering from a complex system. Our model is a
metric graph with a nonlinear Schrödinger (NLS) operator -- a simple
theoretical model either for a BEC in a quasi-1D trap with
non-trivial topology or for an optical fibre network. In the low
intensity limit the NLS operator becomes linear (a quantum graph).
For scattering with very low incoming intensities, one may expect
that the nonlinearity is either irrelevant or may be treated
perturbatively. However, at resonances this expectation often breaks
down as the intensity inside the network may be amplified by some
orders of magnitude (constructive interference on network cycles).
In certain networks narrow resonances with very high amplification
are far more frequent than in most other complex scattering models.
We identify the origin of these resonances which is of topological
nature and derive power laws for the intensity amplification inside
the network.
Get the flier... |
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18 Apr 2012 |
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Dr David Ehre, Department
of Materials and Interfaces, Weizmann Institute |
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Wed
12:00 |
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NON-CRYSTALLINE
PYROELECTRIC AND PIEZOELECTRIC |
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Room 308/8 |
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QUASI-AMORPHOUS IONIC
FILMS |
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Non-crystalline piezoelectric and pyroelectric inorganic thin film
of BaTiO3, SrTiO3
and BaZrO3, called
quasi-amorphous, were investigated. The quasi-amorphous phase of
BaZrO3 and SrTiO3
is the first known instance when a compound that does not form polar
crystalline polymorphs (BaZrO3
and SrTiO3) can form a
non-crystalline polar phase. Several experimental measurements,
including XAFS, XPS and stress measurements, were preformed. Base on
these measurements a model describing formation of these materials
was developed. This model of “Random Network of Local Bonding Units”
is very different from a continuous random network of covalent
glasses and a random close packing of hard spheres of metallic
glasses. The model poses that the amorphous films of BaTiO3,
SrTiO3 and BaZrO3
are composed from asymmetrically distorted TiO6
or ZrO6 octahedra that
randomly share apices, edges or faces. If an amorphous
substrate-supported film is pulled through temperature gradient, it
does not crystallize due to substrate clamping. The temperature
gradient causes partial alignment of the octahedra, imparting the
film with macroscopic dipole moment. Existence of three different
compounds forming quasi-amorphous phases strongly suggests that
formation of the quasi-amorphous phases is a general phenomenon.
Get the flier... |
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16 Apr 2012 |
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Professor Ady Arie,
Department of Physical Electronics, Tel Aviv University |
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Monday
12:00 |
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Room 308/8 |
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BEAM SHAPING AND
CONTROL USING NONLINEAR PHOTONIC CRYSTALS |
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By modulating the quadratic nonlinear coefficient of ferroelectric
crystals, it is possible to simultaneously convert the input
frequency into one of its harmonics and at the same time to change
the shape of the generated beam. I will discuss two methods for
nonlinear beam shaping, based on transverse phase offset and on
nonlinear realization of a computer generated hologram. These
methods are used to nonlinearly generate and manipulate accelerating
Airy beams, parabolic beams and vortex beams, as well as to convert
Hermite Gaussian beam at the fundamental frequency to high order
Hermite Gaussian beams at the second harmonic.
Get the flier... |
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09 Apr 2012 |
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No Seminar
― Passover |
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02 Apr 2012 |
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Professor Yacov Kantor,
School of Physics and Astronomy, Tel Aviv University |
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Monday
12:00 |
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Room 426/8 |
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ENTROPIC FORCES AND
POLYMER CONFIGURATIONS IN CONFINED SPACES |
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The free energy of long polymers is frequently dominated by entropy
with the interaction energy playing a minor role. In the absence of
an energy scale, the corresponding forces are then governed by the
thermal energy scale kT and by the length scales associated
with the experimental set-up. Recent advances in single molecule
manipulation techniques have brought the accuracy of position and
force determination into the range where the measurement of
relatively small deformations becomes possible. In these situations
the detailed shape of probes to which the molecule is attached must
be taken into account. I will discuss the influence of probe shapes
on the elastic properties of polymers.
Get the flier... |
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01 Apr 2012 |
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Dr Michael Kroyter, School of Physics
and Astronomy, Tel Aviv University |
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Sunday
14:00 |
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Room 426/8 |
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STRING FIELD THEORY
FROM A CONDOR'S AND EAGLE'S EYE VIEW |
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String theory holds the promise of unifying all forces of nature.
However, we do not know what string theory is. A possible approach
towards this problem is to define string theory as a field theory of
strings, that is, as a string field theory. In this talk, string
theory will be briefly reviewed and the framework of string field
theory will be motivated. The challenges we face in defining and
working with string field theory, as well as its accomplishments and
some emerging mathematical structures will be presented.
Get the flier... |
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26 Mar 2012 |
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Professor Ora Entin-Wohlman,
Department of Physics, Ben Gurion University |
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Monday
12:00 |
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Room 426/8 |
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THERMOELECTRIC
TRANSPORT IN THREE-TERMINAL JUNCTIONS |
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Heat and charge currents through a junction bridging two electronic
baths (of possibly different temperatures and different chemical
potentials), and coupled to a third thermal terminal are considered.
The role of inelastic processes between the charge carriers
and the thermal terminal is emphasized. The main idea is to try and
force electrons transported through the junction (e.g., a molecular
bridge) to take relatively large energy from the thermal bath and
deliver it to another bath or to an electronic reservoir, as a heat
or a charge current, attempting to achieve a significant figure of
merit for the process.
Get the flier... |
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20 Mar 2012 |
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Dr Izhar Neder, School of
Physics and Astronomy, Tel Aviv University |
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Tuesday
14:00 |
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ELECTRON
INTERFERENCE, NOISE, AND INTERACTIONS IN EDGE |
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Room 426/8 |
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STATES IN THE QUANTUM
HALL EFFECT |
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Recently there is a burst of interest in measurements of
interference patterns and noise of topologically-protected edge
states in the quantum Hall effect regime. One reason for this
interest is the potential of these experiments in demonstrating
fractional and non-Abelian statistics between particles, which may
lead to a realization of quantum computation. Another reason is that
a new and diverse group of experiments revealed a non-trivial
influence of the Coulomb interaction between electrons on the
interference patterns and on the noise, which we only now begin to
understand. In the talk, I will give an overview of various
experiments done in this research field and the connections between
them, and I will outline the theories which we developed in order to
explain their results.
Get the flier... |
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19 Mar 2012 |
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Professor Yuval Garini,
Department of Physics, Bar Ilan University |
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Monday
12:00 |
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THE ROLE OF NANO-OPTICS
IN BIOPHYSICS: STUDYING |
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Room 426/8 |
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DNA-PROTEIN
INTERACTIONS ON A SINGLE-MOLECULE LEVEL |
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Physics now plays an ever growing role for biological research and
medical applications. Biophysics combines the use of state of the
art experimental methods so as new theoretical models. Altogether it
provides better understanding of many biological mechanisms and
leads to improved healthcare. Here I will concentrate mainly on one
example, the study of DNA protein interaction on the single molecule
level. We developed an optical method for studying DNA-protein
interactions on a single-molecule level based on tethered particle
motion (TPM) and the use of gold nano-beads. Using the method, we
measured the three dimensional end-to-end distribution of a DNA
tethered to a wall. It allowed us to gain a better insight on the
DNA conformations as well to study the role of an important
bacterial protein called HU.
Get the flier... |
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12 Mar 2012 |
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Professor Yoav Schechner,
Department of Electrical Engineering, Technion |
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Monday
12:00 |
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Room 426/8 |
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PHYSICS BASED
COMPUTER VISION |
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In a sensing task, particularly imaging, significant benefits are
obtained by considering the physical and computational aspects in a
joint manner. By this we mean that image acquisition is explicitly
affected by the presence of subsequent digital computing, while data
processing is tailored to this acquisition. We show examples of such
joint methods, dealing with all the setup components: illumination,
media, cameras and, finally, computer. Specifically, noise in
measurement arrays is reduced by a multiplexing approach which
considers saturation, photon noise and natural crosstalk. In
addition, images obtained under camera motion can self-calibrate
radiometric imperfections, such as flare. Finally, with the aid of
simple calculations, polarization can dehaze scenes and recover
their 3D structure.
Get the flier... |
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05 Mar 2012 |
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Professor Nir Shaviv,
Racah Institute, Hebrew University of Jerusalem |
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Monday
12:00 |
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Room 426/8 |
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ON COSMIC RAYS AND
CLIMATE |
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Cosmic Rays appear to have a large effect on climate. I will review
the evidence for this link, which exists on all time scales ranging
from days to eons. I will then discuss the implications that this
link has for our understanding of 20th century climate change and
for future warming over the 21st century.
Get the flier... |
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27 Feb 2012 |
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Professor Tamar Seideman,
Department
of Chemistry, Northwestern University |
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Monday
12:00 |
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ULTRAFAST
NANOPLASMONICS: TOWARD INFORMATION GUIDANCE |
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Room 426/8 |
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IN THE NANOSCALE |
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Inelastic electron tunneling via molecular-scale junctions can
induce a variety of fascinating dynamical processes in the molecular
moiety. These include vibration, rotation, inter-mode energy flow
and reaction. Potential applications of current-driven dynamics in
heterojunctions range from new forms of molecular machines and new
modes of conduction, to new directions in surface nanochemistry and
nanolithography. In the first part of the talk, I will discuss the
qualitative physics underlying current driven dynamics in
molecular-scale devices, briefly outline the theory we developed to
explore these dynamics, describe the results of ongoing research on
surface nanochemistry and molecular machines, and sketch several of
our dreams and plans in these areas. The application of light to
control molecular motions and electronic transport in junctions is
intriguing, since photonic (by contrast to electronic) sources offer
(sub) femtosecond time resolution and tunable phase and polarization
properties. One of several challenges, however, is the requirement
of coherent light sources that are tightly localized in space. It is
here that plasmonics offer an opportunity. In the second part of the
talk, we will combine plasmonics physics with concepts and tools
borrowed from coherent control of molecular dynamics with two goals
in mind. One is to introduce new function into nanoplasmonics,
including ultrafast elements and broken symmetry elements. The
second is to develop coherent nanoscale sources and apply them to
coherent control of both molecular dynamics and electric transport
in the nanoscale. To conclude the talk, we will return to
nanoelectronics, and illustrate the application of plasmonics to
control of transport in the nanoscale, with a view to ultrafast
electric switches.
Get the flier... |
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Fall Term |
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23 Jan 2012 |
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Professor Eric Akkermans,
Department
of Physics, Technion |
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Monday
12:00 |
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WAVES AND QUANTUM
FIELDS ON FRACTALS: CONSEQUENCES OF |
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Room 426/8 |
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COMPLEX FRACTAL
DIMENSIONS |
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Fractals define a new and interesting realm for a discussion of
basic phenomena in Quantum Electrodynamics and Statistical
Mechanics. This interest results from specific properties of
fractals, e.g., their dilatation symmetry and the corresponding
absence of Fourier mode decomposition. Moreover, the existence of a
set of distinct dimensions characterizing the physical properties
(spatial or spectral) of fractals make them a useful testing ground
for dimensionality dependent physical problems. We shall start by
noting that the absence of Fourier transform on a fractal implies
necessarily different notions of volume in direct and reciprocal
spaces and thus the need to modify the Heisenberg uncertainty
principle. Implications for field quantization and the definition of
the notion of photon on a fractal will be further addressed. We
shall address specific problems including the behavior of the heat
kernel and zeta functions on fractals and their importance in the
expression of spectral properties in quantum field theory. Finally,
we shall apply these results to specific problems such as
thermodynamics of radiation by a fractal blackbody and a conjecture
regarding the behavior of the non-diagonal heat kernel.
Get the flier... |
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16 Jan 2012 |
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Professor Oded Agam, Racah
Institute, Hebrew University of Jerusalem |
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Monday
12:00 |
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MANIFESTATIONS OF
ELECTRON INTERACTIONS IN PHOTOGALVANIC |
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Room 426/8 |
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EFFECT IN CHIRAL
NANOTUBES |
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We consider the influence of electron-electron interaction on the
photogalvanic effect in carbon nanotubes that are chiral and
metallic. We show that in the limit of strong interactions the
mechanism of photo-induced voltage by circularly polarized light is
analogous to the Mossbauer effect, and that close to the threshold
the photovoltage exhibits a power law singularity characteristic of
one dimensional interacting systems. The power of this singularity
is dictated by the ratio of the electron density to the momentum
shift between the bottoms of the occupied and the first unoccupied
subbands. We also characterize the singularities of the photovoltage
which appear above the threshold at intervals of the Debye frequency
of the plasmons.
Get the flier... |
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09 Jan 2012 |
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Professor Uzy Smilansky,
Physics of Complex Systems, Weizmann Institute |
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Monday
12:00 |
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QUANTUM CHAOS ON
GRAPHS: COMBINATORICS, RANDOM MATRIX THEORY, |
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Room 426/8 |
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AND RANDOM WAVES |
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The spectrum and eigenvectors of the discrete Shroedinger operator
on regular graphs display many features which are typical of quantum
systems with a chaotic classical dynamics. In this talk I shall
describe the findings, compare them to the predictions of random
matrix theory and random wave models, and explain their
combinatorial origin. No knowledge of graph theory is required.
Get the flier... |
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02 Jan 2012 |
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Dr Eran Sela, University of
Cologne, Germany |
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Monday
12:00 |
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Room 426/8 |
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ISING CRITICALITY:
FROM QUANTUM MAGNETISM TO MAJORANA QBITS |
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The Ising model is a paradigmatic example of phase transitions and
critical phenomena, and is still of central importance in modern low
dimensional quantum systems. Importantly this model formulated
originally in terms of spins, has an equivalent fermionic
description. This allows for a unifying formulation of very
different electron systems, ranging from quantum wires supporting
Majorana edge stats to quantum dots in the two channel Kondo
geometry, in terms of analogous magnetic systems. For example, the
two channel Kondo model presents an intriguing and theoretically
difficult problem due to its electronic non-Fermi liquid behavior.
Moreover this critical point is extremely unstable against symmetry
breaking perturbations which make experiments very demanding. Here I
show how the physics of this instability is directly connected with
models of Ising spins. This way, new universal predictions for
quantum dot experiments capturing the entire crossover from
non-Fermi liquid to Fermi liquid will be presented and discussed.
Get the flier... |
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26 Dec 2011 |
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Professor Boris Fainberg,
Holon Institute of Technology |
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Monday
12:00 |
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ENERGY TRANSFER,
COULOMB BLOCKING AND PLASMONIC EFFECTS |
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Room 426/8 |
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ON
CURRENT-VOLTAGE CHARACTERISTICS OF MOLECULAR JUNCTIONS |
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Molecular electronics is one of the most promising substitutes for
today's semiconductor electronics. In this connection, molecular
conduction nanojunctions have been under intensive studies in the
last few years. We study effects of energy transfer and Coulomb
blocking in a molecular bridge, and the plasmonic effects due to the
metal contacts on the current-voltage characteristics of molecular
conduction nanojunctions. We predict new effects of "exciton"
blocking the current and compensation of Coulomb blocking by energy
transfer.
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19 Dec 2011 |
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Professor Michael Galperin,
University of California at San Diego |
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Monday
12:00 |
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Room 426/8 |
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RAMAN SPECTROSCOPY
OF MOLECULAR JUNCTIONS |
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Recent advances in experimental techniques at nanoscale, and in
particular Raman scattering measurements on current-carrying single
molecule junctions, promises to become a superior diagnostic tool.
Theoretical understanding of optical response of open molecular
systems far from equilibrium is of major importance for development
of molecular optoelectronic devices. Within simple models we
consider intra-molecular and charge-transfer contributions to Raman
spectroscopy of molecular junction. We also discuss a concept of
"effective temperature", its relevance in representation of
bias-induced heating, and ability of Raman measurements to provide
information on the latter.
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12 Dec 2011 |
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Professor Eran Sharon,
Racah Institute, Hebrew University of Jerusalem |
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Monday
12:00 |
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THE MECHANICS OF
POD OPENING AND ITS RELATION |
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Room 426/8 |
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TO SELF-ASSEMBLED
CHIRAL MICROMOLECULES |
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We study the geometry and mechanics that drive the opening of
Bauhinia seeds pods. The pod valve wall consists of two fibrous
layers oriented at (plus/minus) 45^o with respect to the pod axis.
Upon drying, each of the layers shrinks uniaxially, perpendicularly
to the fibers orientation. This active deformation turns the valve
into an incompatible sheet with reference saddle-like curvature
tensor and a flat (Euclidean) reference metric. These two intrinsic
properties are incompatible. The shape is, therefore, selected by a
stretching-bending competition. Strips cut from the valve tissue and
from synthetic model material adopt various helical configurations.
We provide analytical expressions for these configurations in the
bending and stretching dominated regimes and show how plants use
these mechanical principles using different tissue architectures.
Finally, we point to geometrical and mechanical equivalence between
elastic strips with negative reference curvature and self assembled
macromolecules made of twisted elements. Based on this equivalence
we provide explanation and quantitative predictions for shape
transitions that have been observed in self assembled
macromolecules.
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05 Dec 2011 |
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Professor David Gershoni,
Department
of Physics, Technion |
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Monday
12:00 |
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Room 426/8 |
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SPINNING THE
ELECTRONIC SPIN |
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Semiconductor materials form the basis of modern electronics,
communication, data storage and computing technologies, which shape
our civilization. Two conditions make these materials
technologically important: precise control of electric charge
transport in them and the ability to efficiently generate and detect
light. Future technologies demand realization of methods and devices
for controlling the electronic spin, as well. Control over the
electronic spin, opens up novel technological horizons, since it
largely increases the information that an electron may carry and
transmit. Semiconductor quantum dots are often referred to as
"artificial-atoms" and much like real atoms, confined electrons in
these dots have discrete energy spectrum. The absorption of a photon
(the quantum of light) excites an electron, where the energy of the
photon is transferred to the electron and its polarization (the
direction at which the electric field is oscillating) is transferred
to the electrons' spin state. We demonstrate ability to write and
read the state of the electronic spin directly using polarized
pulsed resonant optical excitation. We also show for the first time,
a full control over the direction of the spin of the electronic
excitation by being able to rotate it to our desire. We do all these
operations using a single, short laser pulse.
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01 Dec 2011 |
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Professor Uzi Even, School
of Chemistry, Tel Aviv University |
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Thursday
12:00 |
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Room 426/8 |
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IS NUCLEAR ENERGY
AN OPTION AFTER FUKUSHIMA? |
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We examine the economic, safety record and new reactors to supply
the future energy needs of industrial societies in general and
Israel in particular.
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24 Nov 2011 |
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Dr Daniel Podolsky,
Department of Physics, Technion |
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Thursday
12:00 |
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VISIBILITY OF THE
AMPLITUDE (HIGGS) MODE IN |
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Room 426/8 |
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CONDENSED MATTER |
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The amplitude mode, the analogue of the Higgs particle, is a
ubiquitous collective excitation in condensed matter systems with
broken continuous symmetry. It is expected to appear in
antiferromagnets, short coherence length superconductors, charge
density waves, and superfluids near the Mott transition. Detection
of the amplitude mode is a valuable test of the underlying field
theory, and its mass gap is a measure of proximity to a quantum
critical point. However, since the amplitude mode can decay into low
energy Goldstone modes, its experimental visibility has been
questioned. Here we show that the visibility depends on the symmetry
of the measured susceptibility. In particular, scalar (rotationally
invariant) measurements allow for the observation of a sharp
amplitude peak throughout the ordered phase. I will propose
experimental setups to measure the amplitude peak across many
physical systems.
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17 Nov 2011 |
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Professor Ron Folman,
Department of Physics, Ben Gurion University |
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Thursday
12:00 |
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Room 426/8 |
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ATOM CHIPS FOR
QUANTUM INFORMATION PROCESSING |
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In this talk I will briefly review the basics of a device called the
atom chip in which quantum systems (e.g. ultra cold atoms) are
trapped and manipulated microns from the classical environment of a
room temperature surface. I will describe the underlying physics
governing this combined apparatus (e.g. coupling through the highest
temperature gradient ever created in a lab). All this will be
detailed in the context of material science which allows us to
engineer the surface environment so as to accommodate fundamental
studies as well as technological applications. Specifically, I will
note the advantages and disadvantages when aiming at realizing a
quantum information device.
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10 Nov 2011 |
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Dr Yossi Paltiel,
Department of Applied Physics, Hebrew University of Jerusalem |
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Thursday
12:00 |
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Room 426/8 |
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MIMICKING THE
NATURE APPROACH TO QUANTUM MECHANICS |
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Quantum nano-structures are likely to become primary components of
future electronic devices. Practical realization of quantum devices
faces a number of challenges. However, the benefits from the
successful implementation of these devices can be enormous. Nature
in several cases uses quantum mechanics in order to achieve
extraordinary properties. One known examples is the high photon
conversion efficiency in photosynthetic light harvesting complexes.
In this example the most striking feature is the use of coherence
properties and quantum mechanics in the short scale while the
measurements and results are classical in the large scale. In my lab
I aim to mimic nature and create nano tool box bottom up approach
which enables high temperature quantum operation coupled to top down
classical semiconductor measurement device. This methodology is
producing a generic technology for constructing nano-systems in
which many devices are interconnected and operate in unison, without
inhibiting their quantum nature. In the talk we will present our
efforts to achieve confinement potential control using different
dots systems as well as charge and spin transfer control in our
hybrid dots systems. We will show our recent results in which we
were able to discover a collective electron transfer process by
studying the current noise in a field effect transistor with
light-sensitive gate formed by nanocrystals linked by organic
molecules to its surface. A demonstration of a room temperature
operating hybrid quantum sensor will be presented together with
quantum room temperature transport properties using several hybrid
layers. We hope that by controlling the quantum and classical
behavior of the self assembled layers we will be able to create
novel and revolutionary devices mimicking some of Nature's complex
structures. One such example would be mimicking the light harvesting
complexes in a controlled self assembled design. Using the
flexibility of the design we can realize systems which will test the
some of the suggested quantum theories. Further into the future we
aim to use this knowledge for applicable devices such as increasing
the efficiency of solar cells coupled to simple Si based devices.
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31 Oct 2011 |
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Professor David Tannor,
Department of Chemical Physics, Weizmann Institute |
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Monday 12:00 |
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BOHMIAN MECHANICS
WITH COMPLEX ACTION: A NEW FORMULATION |
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Room 426/8 |
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OF QUANTUM MECHANICS
WITH COMPLEX TRAJECTORIES |
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Ever since the advent of Quantum Mechanics, there has been a quest
for a trajectory-based formulation of quantum theory that is exact.
In the 1950’s, David Bohm, building on earlier work of Madelung and
de Broglie, developed an exact formulation of quantum mechanics in
which trajectories evolve in the presence of the usual Newtonian
force plus an additional quantum force. In recent years, there has
been a resurgence of interest in Bohmian Mechanics (BM) as a
numerical tool because of its apparently local dynamics. However,
closer inspection of the Bohmian formulation reveals that the
nonlocality of quantum mechanics has not disappeared -- it has
simply been swept under the rug into the quantum force. In this
work, we present a new formulation of Bohmian mechanics in which the
quantum action, S, is taken to be complex. This requires the
propagation of complex trajectories, but with the reward of a
significantly higher degree of localization. For example, using
strictly localized trajectories (no communication with their
neighbors) we are able to obtain one- and two-dimensional tunneling,
interference, thermal rate constants and eigenvalues. Recently we
have extended the method to non-adiabatic transitions, where rather
than hopping from surface to surface the trajectories affect their
counterparts on the other surfaces via the difference in their
complex phase. On the formal side, the approach is shown to be a
rigorous extension of generalized Gaussian wavepacket methods to
obtain exact quantum mechanics, and has intriguing implications for
fundamental quantum mechanics.
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