13,194 research outputs found
A widely tunable few electron droplet
Quasi-static transport measurements are employed to characterize a few
electron quantum dot electrostatically defined in a GaAs/AlGaAs
heterostructure. The gate geometry allows observations on one and the same
electron droplet within a wide range of coupling strengths to the leads. The
weak coupling regime is described by discrete quantum states. At strong
interaction with the leads Kondo phenomena are observed as a function of a
magnetic field. By varying gate voltages the electron droplet can, in addition,
be distorted into a double quantum dot with a strong interdot tunnel coupling
while keeping track of the number of trapped electrons.Comment: 11 pages, 5 figure
Existence and Vanishing of the Breathing Mode in Strongly Correlated Finite Systems
One of the fundamental eigenmodes of finite interacting systems is the mode
of {\em uniform radial expansion and contraction} -- the ``breathing'' mode
(BM). Here we show in a general way that this mode exists only under special
conditions: i) for harmonically trapped systems with interaction potentials of
the form or , or ii) for
some systems with special symmetry such as single shell systems forming
platonic bodies. Deviations from the BM are demonstrated for two examples:
clusters interacting with a Lennard-Jones potential and parabolically trapped
systems with Yukawa repulsion. We also show that vanishing of the BM leads to
the occurence of multiple monopole oscillations which is of importance for
experiments
Cyber Security Awareness Among College Students
This study reports the early results of a study aimed to investigate student awareness and attitudes toward cyber security and the resulting risks in the most advanced technology environment: the Silicon Valley in California, USA. The composition of students in Silicon Valley is very ethnically diverse. The objective was to see how much the students in such a tech-savvy environment are aware of cyber-attacks and how they protect themselves against them. The early statistical analysis suggested that college students, despite their belief that they are observed when using the Internet and that their data is not secure even on university systems, are not very aware of how to protect their data. Also, it appears that educational institutions do not have an active approach to improve awareness among college students to increase their knowledge on these issues and how to protect themselves from potential cyber-attacks, such as identity theft or ransomware
Chlorinated auxinsâhow does Arabidopsis thaliana deal with them?
Plant hormones have various functions in plants and play crucial roles in all developmental and differentiation stages. Auxins constitute one of the most important groups with the major representative indole-3-acetic acid (IAA). A halogenated derivate of IAA, 4-chloro-indole-3-acetic acid (4-Cl-IAA), has previously been identified in Pisum sativum and other legumes. While the enzymes responsible for the halogenation of compounds in bacteria and fungi are well studied, the metabolic pathways leading to the production of 4-Cl-IAA in plants, especially the halogenating reaction, are still unknown. Therefore, bacterial flavin-dependent tryptophan-halogenase genes were transformed into the model organism Arabidopsis thaliana. The type of chlorinated indole derivatives that could be expected was determined by incubating wild type A. thaliana with different Cl-tryptophan derivatives. We showed that, in addition to chlorinated IAA, chlorinated IAA conjugates were synthesized. Concomitantly, we found that an auxin conjugate synthetase (GH3.3 protein) from A. thaliana was able to convert chlorinated IAAs to amino acid conjugates in vitro. In addition, we showed that the production of halogenated tryptophan (Trp), indole-3-acetonitrile (IAN) and IAA is possible in transgenic A. thaliana in planta with the help of the bacterial halogenating enzymes. Furthermore, it was investigated if there is an effect (i) of exogenously applied Cl-IAA and Cl-Trp and (ii) of endogenously chlorinated substances on the growth phenotype of the plants
Time scale, objectivity and irreversibility in quantum mechanics
It is argued that setting isolated systems as primary scope of field theory
and looking at particles as derived entities, the problem of an objective
anchorage of quantum mechanics can be solved and irreversibility acquires a
fundamental role. These general ideas are checked in the case of the Boltzmann
description of a dilute gas.Comment: 13 pages, latex, no figures, to appear in the Proceedings of the XXI
International Colloquium on Group Theoretical Methods in Physics, 1996
(Goslar, Germany
Optomechanical circuits for nanomechanical continuous variable quantum state processing
We propose and analyze a nanomechanical architecture where light is used to
perform linear quantum operations on a set of many vibrational modes. Suitable
amplitude modulation of a single laser beam is shown to generate squeezing,
entanglement, and state-transfer between modes that are selected according to
their mechanical oscillation frequency. Current optomechanical devices based on
photonic crystals may provide a platform for realizing this scheme.Comment: 11 pages, 5 figure
Measurement of the Transmission Phase of an Electron in a Quantum Two-Path Interferometer
A quantum two-path interferometer allows for direct measurement of the
transmission phase shift of an electron, providing useful information on
coherent scattering problems. In mesoscopic systems, however, the two-path
interference is easily smeared by contributions from other paths, and this
makes it difficult to observe the \textit{true} transmission phase shift. To
eliminate this problem, multi-terminal Aharonov-Bohm (AB) interferometers have
been used to derive the phase shift by assuming that the relative phase shift
of the electrons between the two paths is simply obtained when a smooth shift
of the AB oscillations is observed. Nevertheless the phase shifts using such a
criterion have sometimes been inconsistent with theory. On the other hand, we
have used an AB ring contacted to tunnel-coupled wires and acquired the phase
shift consistent with theory when the two output currents through the coupled
wires oscillate with well-defined anti-phase. Here, we investigate thoroughly
these two criteria used to ensure a reliable phase measurement, the anti-phase
relation of the two output currents and the smooth phase shift in the AB
oscillation. We confirm that the well-defined anti-phase relation ensures a
correct phase measurement with a quantum two-path interference. In contrast we
find that even in a situation where the anti-phase relation is less
well-defined, the smooth phase shift in the AB oscillation can still occur but
does not give the correct transmission phase due to contributions from multiple
paths. This indicates that the phase relation of the two output currents in our
interferometer gives a good criterion for the measurement of the \textit{true}
transmission phase while the smooth phase shift in the AB oscillation itself
does not.Comment: 5 pages, 4 figure
Kondo effect in a one-electron double quantum dot: Oscillations of the Kondo current in a weak magnetic field
We present transport measurements of the Kondo effect in a double quantum dot
charged with only one or two electrons, respectively. For the one electron case
we observe a surprising quasi-periodic oscillation of the Kondo conductance as
a function of a small perpendicular magnetic field |B| \lesssim 50mT. We
discuss possible explanations of this effect and interpret it by means of a
fine tuning of the energy mismatch of the single dot levels of the two quantum
dots. The observed degree of control implies important consequences for
applications in quantum information processing
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