4,467 research outputs found
Advanced algorithms for the analysis of data sequences in Matlab
Cílem této práce je se seznámení s možnostmi programu Matlab z hlediska detailní analýzy deterministických dynamických systémů. Jedná se především o analýzu časové posloupnosti a o nalezení Lyapunových exponentů. Dalším cílem je navrhnout algoritmus umožňující specifikovat chování systému na základě znalosti příslušných diferenciálních rovnic. To znamená, nalezení chaotických systémů.This work aims to familiarize with the possibilities of Matlab in terms of detailed analysis of deterministic dynamical systems. This is essentially a analysis of time series and finding Lyapunov exponents. Another objective is to design an algorithm allowing to specify the system behavior based on knowledge of the relevant differential equations. That means finding chaotic systems.
Qualitative modeling of chaotic logical circuits and walking droplets: a dynamical systems approach
Logical circuits and wave-particle duality have been studied for most of the 20th century. During the current century scientists have been thinking differently about these well-studied systems. Specifically, there has been great interest in chaotic logical circuits and hydrodynamic quantum analogs.
Traditional logical circuits are designed with minimal uncertainty. While this is straightforward to achieve with electronic logic, other logic families such as fluidic, chemical, and biological, naturally exhibit uncertainties due to their inherent nonlinearity. In recent years, engineers have been designing electronic logical systems via chaotic circuits. While traditional boolean circuits have easily determined outputs, which renders dynamical models unnecessary, chaotic logical circuits employ components that behave erratically for certain inputs.
There has been an equally dramatic paradigm shift for studying wave-particle systems. In recent years, experiments with bouncing droplets (called walkers) on a vibrating fluid bath have shown that quantum analogs can be studied at the macro scale. These analogs help us ask questions about quantum mechanics that otherwise would have been inaccessible. They may eventually reveal some unforeseen properties of quantum mechanics that would close the gap between philosophical interpretations and scientific results.
Both chaotic logical circuits and walking droplets have been modeled as differential equations. While many of these models are very good in reproducing the behavior observed in experiments, the equations are often too complex to analyze in detail and sometimes even too complex for tractable numerical solution. These problems can be simplified if the models are reduced to discrete dynamical systems. Fortunately, both systems are very naturally time-discrete. For the circuits, the states change very rapidly and therefore the information during the process of change is not of importance. And for the walkers, the position when a wave is produced is important, but the dynamics of the droplets in the air are not.
This dissertation is an amalgam of results on chaotic logical circuits and walking droplets in the form of experimental investigations, mathematical modeling, and dynamical systems analysis. Furthermore, this thesis makes connections between the two topics and the various scientific disciplines involved in their studies
Symmetry in Chaotic Systems and Circuits
Symmetry can play an important role in the field of nonlinear systems and especially in the design of nonlinear circuits that produce chaos. Therefore, this Special Issue, titled “Symmetry in Chaotic Systems and Circuits”, presents the latest scientific advances in nonlinear chaotic systems and circuits that introduce various kinds of symmetries. Applications of chaotic systems and circuits with symmetries, or with a deliberate lack of symmetry, are also presented in this Special Issue. The volume contains 14 published papers from authors around the world. This reflects the high impact of this Special Issue
Quantum shot noise in mesoscopic superconductor-semiconductor heterostructures
Shot noise in a mesoscopic electrical conductor have become one of the most attentiondrawing
subject over the last decade. This is because the shot-noise measurements
provide a powerful tool to study charge transport in mesoscopic systems [1]. While
conventional resistance measurements yield information on the average probability
for the transmission of electrons from source to drain, shot-noise provides additional
information on the electron transfer process, which can not be obtained from resistance
measurements. For example, one can determine the charge ‘q’ of the current
carrying quasi-particles in different systems from the Poisson shot noise SI = 2q�I� [2] where �I� is the mean current of the system. For instance, the quasi-particle
charge is a fraction of the electron charge ‘e’ in the fractional quantum Hall regime
[3, 4, 5]. The multiple charge quanta were observed in an atomic point contact
between two superconducting electrodes [6].
Shot-noise also provides information on the statistics of the electron transfer.
Shot noise in general is suppressed from its classical value SI = 2e�I�, due to the
correlations. In mesoscopic conductors, due to the Pauli principle in fermion statistics,
electrons are highly correlated. As a results, the noise is fully suppressed in the
limit of a perfect open channel T = 1. For the opposite limit of low transmission
T � 1, transmission of electron follows a Poisson process and recovers the Schottky
result SI = 2e�I� [2]. For many channel systems, shot-noise is suppressed to
1/2 × 2e�I� for a symmetric double barrier junction [7, 8], to 1/3 in a disordered
wire [9, 10, 11, 12, 13, 14] and to 1/4 in an open chaotic cavity [15, 16, 17].
When a superconductor is involved, the shot-noise can be enhanced by virtue
of the Andreev reflection process taking place at the interface between a normal
metal and a superconductor. In some limiting cases, e.g. in the tunneling and
disordered limit, the shot-noise can be doubled with respect to its normal state
value [18, 19, 20, 21]. One of the main results of this thesis is an extensive comparison
of our experimental data on conductance and shot noise measurements in a S-N
junction with various theoretical models.
In addition to measure shot-noise in a two-terminal geometry, one can also perform
the fluctuation measurements on multi-terminal conductors. Whereas shotnoise corresponds to the autocorrelation of fluctuations from the same leads, crosscorrelation
measurements of fluctuations between different leads provide a wealth of
new experiments. For example, the exchange-correlations can be measured directly
from these geometry [22]. Experimental attempt in mesoscopic electronic device was
the correlation measurements [14, 23] on electron beam-splitter geometry [24] which
is the analogue to the Hanbury-Brown Twiss (HBT) experiment in optics. In their
experiment, Hanbury-Brown and Twiss demonstrated the intensity-intensity correlations
of the light of a star in order to determine its diameter [25]. They measured
a positive correlations between two different output photon beams as predicted to
the particles obeying Bose-Einstein statistics. This behavior is often called ‘bunching’.
On the other hand, a stream of the particles obeying Fermi-Dirac statistics
is expected to show a anti-bunching behavior, resulting in a negative correlation of
the intensity fluctuations. Latter one was confirmed by a Fermionic version of HBT
experiments in single-mode, high-mobility semiconductor 2DEG systems [14, 23].
Whereas in a single electron picture, correlations between Fermions are always
negative1 (anti-bunching), the correlation signal is expected to become positive if
two electrons are injected simultaneously to two arms and leave the device through
different leads for the coincident detection in both outputs2. One simple example is
the splitting of the cooper pair in a Y-junction geometry in front of the superconductor.
Fig.1.1 shows the possible experimental scheme of the correlation measurement
as described here and the sample realized in an high-mobility semiconductor heterostructures.
Since all three experiments were done3, only one left unfolded, ‘The
positive correlations from the Fermionic system’. The main motivation of this thesis
work was to find a positive correlations in the device shown in Fig.1.1. In a
well defined single channel collision experiment on an electron beam splitter, it has
theoretically been shown that the measured correlations are sensitive to the spin
entanglement [29, 30]. This is another even more exciting issue and we would like
to mention that the experimental quest for positive correlations is important for the
new field of quantum computation and communication in the solid state, [31, 32]
in which entangled electrons play a crucial role. A natural source of entanglement
is found in superconductors in which electrons are paired in a spin-singlet
state. A source of entangled electrons may therefore be based on a superconducting
injector.[33, 34, 27, 35, 36, 37, 38, 38, 39, 40, 41] Even more so, an electronic beamsplitter
is capable of distinguishing entangled electrons from single electrons.[29, 42]
However, the positive correlations have not been observed in solid-state mesoscopic
devices until today. This thesis is organized as follows. Chapter 2 is devoted to the theoretical
background of the electrical transport and the current fluctuations. We introduce
the basic concept of electrical transport and the shot noise in normal state and
superconductor-normal metal (S-N) junction. We also briefly review the theoretical
proposals and arguments about the current-current cross-correlations in threeterminal
systems. In Chapter 3, we describe the sample fabrication techniques which
have been done in our laboratory such as e-beam lithography, metallization and etching.
We present also the characterization of our particular system, niobium (Nb) /
InAs-based 2DEG junction. Chapter 4 describes the reliable low-temperature measurement
technique for detecting the noise. We characterize our measurement setup
using a simple RC-circuit model. In Chapter 5, our main results about the shot
noise of S-N junction are presented in detail
Spin-Mediated Consciousness: Theory, Experimental Studies, Further Development & Related Topics
We postulate that consciousness is intrinsically connected to quantum spin
since the latter is the origin of quantum effects in both Bohm and Hestenes
quantum formulisms and a fundamental quantum process associated with the
structure of space-time. Applying these ideas to the particular structures and
dynamics of the brain, we have developed a detailed model of quantum
consciousness. We have also carried out experiments from the perspective of our
theory to test the possibility of quantum-entangling the quantum entities
inside the brain with those of an external chemical substance. We found that
applying magnetic pulses to the brain when an anaesthetic was placed in between
caused the brain to feel the effect of said anaesthetic as if the test subject
had actually inhaled the same. We further found that drinking water exposed to
magnetic pulses, laser light or microwave when an anaesthetic was placed in
between also causes brain effects in various degrees. Additional experiments
indicate that the said brain effect is indeed the consequence of quantum
entanglement. Recently we have studied non-local effects in simple physics
systems. We have found that the pH value, temperature and gravity of a liquid
in the detecting reservoirs can be non-locally affected through manipulating
another liquid in a remote reservoir quantum-entangled with the former. In
particular, the pH value changes in the same direction as that being
manipulated; the temperature can change against that of local environment; and
the gravity can change against local gravity. We suggest that they are mediated
by quantum entanglement between nuclear and/or electron spins in treated liquid
and discuss the profound implications of these results. This paper now also
includes materials on further development of the theory and related topics.Comment: 92 pages; expanded content; minor corrections; for additional
information, please visit http://quantumbrain.or
Is it the boundaries or disorder that dominates electron transport in semiconductor `billiards'?
Semiconductor billiards are often considered as ideal systems for studying
dynamical chaos in the quantum mechanical limit. In the traditional picture,
once the electron's mean free path, as determined by the mobility, becomes
larger than the device, disorder is negligible and electron trajectories are
shaped by specular reflection from the billiard walls alone. Experimental
insight into the electron dynamics is normally obtained by magnetoconductance
measurements. A number of recent experimental studies have shown these
measurements to be largely independent of the billiards exact shape, and highly
dependent on sample-to-sample variations in disorder. In this paper, we discuss
these more recent findings within the full historical context of work on
semiconductor billiards, and offer strong evidence that small-angle scattering
at the sub-100 nm length-scale dominates transport in these devices, with
important implications for the role these devices can play for experimental
tests of ideas in quantum chaos.Comment: Submitted to Fortschritte der Physik for special issue on Quantum
Physics with Non-Hermitian Operator
From Quantum Optics to Quantum Technologies
Quantum optics is the study of the intrinsically quantum properties of light.
During the second part of the 20th century experimental and theoretical
progress developed together; nowadays quantum optics provides a testbed of many
fundamental aspects of quantum mechanics such as coherence and quantum
entanglement. Quantum optics helped trigger, both directly and indirectly, the
birth of quantum technologies, whose aim is to harness non-classical quantum
effects in applications from quantum key distribution to quantum computing.
Quantum light remains at the heart of many of the most promising and
potentially transformative quantum technologies. In this review, we celebrate
the work of Sir Peter Knight and present an overview of the development of
quantum optics and its impact on quantum technologies research. We describe the
core theoretical tools developed to express and study the quantum properties of
light, the key experimental approaches used to control, manipulate and measure
such properties and their application in quantum simulation, and quantum
computing.Comment: 20 pages, 3 figures, Accepted, Prog. Quant. Ele
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