7,234 research outputs found
Scalable Ellipsoidal Classification for Bipartite Quantum States
The Separability Problem is approached from the perspective of Ellipsoidal
Classification. A Density Operator of dimension N can be represented as a
vector in a real vector space of dimension , whose components are the
projections of the matrix onto some selected basis. We suggest a method to test
separability, based on successive optimization programs. First, we find the
Minimum Volume Covering Ellipsoid that encloses a particular set of properly
vectorized bipartite separable states, and then we compute the Euclidean
distance of an arbitrary vectorized bipartite Density Operator to this
ellipsoid. If the vectorized Density Operator falls inside the ellipsoid, it is
regarded as separable, otherwise it will be taken as entangled. Our method is
scalable and can be implemented straightforwardly in any desired dimension.
Moreover, we show that it allows for detection of Bound Entangled StatesComment: 8 pages, 5 figures, 3 tables. Revised version, to appear in Physical
Review
A Photonic Implementation for the Topological Cluster State Quantum Computer
A new implementation of the topological cluster state quantum computer is
suggested, in which the basic elements are linear optics, measurements, and a
two-dimensional array of quantum dots. This overcomes the need for non-linear
devices to create a lattice of entangled photons. We give estimates of the
minimum efficiencies needed for the detectors, fusion gates and quantum dots,
from a numerical simulation
Policy Gradient Approach to Compilation of Variational Quantum Circuits
We propose a method for finding approximate compilations of quantum unitary
transformations, based on techniques from policy gradient reinforcement
learning. The choice of a stochastic policy allows us to rephrase the
optimization problem in terms of probability distributions, rather than
variational gates. In this framework, finding the optimal configuration is done
by optimizing over distribution parameters, rather than over free angles. We
show numerically that this approach can be more competitive than gradient-free
methods, for comparable amounts of resources (i.e. quantum circuit runs).
Another interesting feature of this approach to variational compilation is that
it does not need a separate register and long-range interactions to estimate
the end-point fidelity, which is an improvement over methods which rely on the
Hilbert-Schmidt test. We expect these techniques to be relevant for training
variational circuits in other contexts
Entanglement-Enhanced Classical Communication
This thesis will be focused on the classical capacity of quantum channels,
one of the first areas treated by quantum information theorists. The problem is
fairly solved since some years. Nevertheless, this work will give me a reason
to introduce a consistent formalism of the quantum theory, as well as to review
fundamental facts about quantum non-locality and how it can be used to enhance
communication. Moreover, this reflects my dwelling in the spirit of classical
information theory, and it is intended to be a starting point towards a
thorough study of how quantum technologies can help to shape the future of
telecommunications.
Whenever it was possible, heuristic reasonings were introduced instead of
rigorous mathematical proofs. This finds an explanation in that I am a
self-taught neophyte in the field, and just about every time I came across a
new concept, physical arguments were always more compelling to me than just
maths. The technical content of the thesis is twofold. On one hand, a quadratic
classification based on optimization programs that I devised for distinguishing
entangled states is presented in Chapter 4. In second place, a less difficult
yet I hope equally interesting technical part consists of versions of some
proofs throughout the text.Comment: M.Sc. Thesis, 103 page
Periodic skyrmionic textures via conformal cartographic projections
We find periodic skyrmionic textures via conformal cartographic projections
that map either an entire spherical parameter space or a hemisphere onto every
regular polygon that provides regular tessellations of the plane. These maps
preserve the sign of the Skyrme density throughout the entire space. We
implement these textures in the polarization state of a laser beam, and
demonstrate that paraxial fields where a periodic texture preserving the sign
of the Skyrme density is implemented in the polarization state distribution
unavoidably exhibit zeros
Remote lab experiments: opening possibilities for distance learning in engineering fields
Remote experimentation laboratories are systems based on real equipment, allowing students to perform practical work through a computer connected to the internet. In engineering fields lab activities play a fundamental role. Distance learning has not demonstrated good results in engineering fields because traditional lab activities cannot be covered by this paradigm. These activities can be set for one or for a group of students who work from different locations. All these configurations lead to considering a flexible model that covers all possibilities (for an individual or a group). An inter-continental network of remote laboratories supported by both European and Latin American institutions of higher education has been formed. In this network context, a learning collaborative model for students working from different locations has been defined. The first considerations are presented.Education for the 21 st century - impact of ICT and Digital Resources ConferenceRed de Universidades con Carreras en Informática (RedUNCI
Implementations of Fault-tolerant Quantum Devices
Accurate control and addressability of quantum devices will come with the
promise of improvement in a wide variety of theoretical and applied fields, such as
chemistry, condensed matter physics, theoretical computer science, foundational
physics, communications, metrology and others.
Decoherence of quantum states and the loss of quantum systems have adverse effects and deter a satisfactory usage of quantum devices. This is the main problem
to be overcome, which is the goal of quantum fault tolerance. In this thesis
we present a series of works that contribute to some of the fields mentioned above,
in the direction of fighting decoherence and loss.
These works fall in two categories: on one hand, we looked at computer architectures
which can be used to combat errors, using techniques of quantum error
correcting codes. In a first project we found decoherence and loss probability
thresholds below which quantum computing is provably possible. We assumed a
very particular error model tailored specially to quantum dots as single photon
sources and linear optics. Subsequently we looked at the problem of loss, both
of heralded and unheralded, and devised some ways to fight it. The framework
under which this work was done was used to develop theory which is currently
being tested in a quantum optics experimental group and will be reported in an
article later this year.
On the other hand, we studied how the error probability can be reduced at
the physical level, thanks exclusively to the properties of the system in which
information is stored, as opposed to making use of quantum codes. We looked
at a particular superconducting circuit, which is potentially very well protected
against some types of decoherence. In particular, we observed that the interaction
with the environment become weaker for certain values of the circuit external
parameters
Quality Parameters of Wet and Dry Aged Beef Loins from Cattle Fed High Doses of Vitamin E
The objective of this experiment was to determine if dietary supplementation of high doses of vitamin E (alpha-tocopherol; 2,200 IU per day for 100 days) can impact quality attributes of wet and dry-aged beef strip loins. Steaks from beef cattle supplemented with high doses of vitamin E exhibited less lipid oxidation after wet or dry aging, took longer time to discolor during retail display, and sustained redder color for a longer period under retail display conditions compared to controls. Free amino acids related to positive beef flavor attributes were higher for dry-aged loins compared to traditional wet aged samples loins. In dry-aged beef, trained sensory panelists found fewer negative flavors in beef from cattle fed high doses of vitamin E compared to controls. Dietary supplementation of high vitamin E levels can reduce lipid oxidation during wet or dry aging, improve color stability during retail display, reduce off flavors and maintain red color for a longer period under retail display conditions compared to controls
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