278 research outputs found
Chaotic spin-spin entanglement on a recursive lattice
We propose an exactly solvable multisite interaction spin-1/2
Ising-Heisenberg model on a triangulated Husimi lattice for the rigorous
studies of chaotic entanglement. By making use of the generalized star-triangle
transformation, we map the initial model onto an effective Ising one on a
Husimi lattice, which we solve then exactly by applying the recursive method.
Expressing the entanglement of the Heisenberg spins, that we quantify by means
of the concurrence, in terms of the magnetic quantities of the system, we
demonstrate its bifurcation and chaotic behavior. Furthermore, we show that the
underlying chaos may slightly enhance the amount of the entanglement, and
present on the phase diagram the transition lines from the uniform to periodic
and from the periodic to chaotic regimes.Comment: 12 pages, 7 figures. Updated version for publicatio
Clustering for Different Scales of Measurement - the Gap-Ratio Weighted K-means Algorithm
This paper describes a method for clustering data that are spread out over
large regions and which dimensions are on different scales of measurement. Such
an algorithm was developed to implement a robotics application consisting in
sorting and storing objects in an unsupervised way. The toy dataset used to
validate such application consists of Lego bricks of different shapes and
colors. The uncontrolled lighting conditions together with the use of RGB color
features, respectively involve data with a large spread and different levels of
measurement between data dimensions. To overcome the combination of these two
characteristics in the data, we have developed a new weighted K-means
algorithm, called gap-ratio K-means, which consists in weighting each dimension
of the feature space before running the K-means algorithm. The weight
associated with a feature is proportional to the ratio of the biggest gap
between two consecutive data points, and the average of all the other gaps.
This method is compared with two other variants of K-means on the Lego bricks
clustering problem as well as two other common classification datasets.Comment: 13 pages, 6 figures, 2 tables. This paper is under the review process
for AIAP 201
A compact entanglement distillery using realistic quantum memories
We adopt the beam splitter model for losses to analyse the performance of a
recent compact continuous-variable entanglement distillation protocol [Phys.
Rev. Lett. 108, 060502, (2012)] implemented using realistic quantum memories.
We show that the decoherence undergone by a two-mode squeezed state while
stored in a quantum memory can strongly modify the results of the preparatory
step of the protocol. We find that the well-known method for locally increasing
entanglement, phonon subtraction, may not result in entanglement gain when
losses are taken into account. Thus, we investigate the critical number
of phonon subtraction attempts from the matter modes of the quantum memory. If
the initial state is not de-Gaussified within attempts, the protocol
should be restarted to obtain any entanglement increase. Moreover, the
condition implies an additional constraint on the subtraction beam
splitter interaction transmissivity, viz. it should be about 50% for a wide
range of protocol parameters. Additionally, we consider the average
entanglement rate, which takes into account both the unavoidable probabilistic
nature of the protocol and its possible failure as a result of a large number
of unsuccessful subtraction attempts. We find that a higher value of the
average entanglement can be achieved by increasing the subtraction beam
splitter interaction transmissivity. We conclude that the compact distillation
protocol with the practical constraints coming from realistic quantum memories
allows a feasible experimental realization within existing technologies.Comment: 9 pages, 8 figures. Updated version for publicatio
Generation of entanglement in systems of intercoupled qubits
We consider systems of two and three qubits, mutually coupled by
Heisenberg-type exchange interaction and interacting with external laser
fields. We show that these systems allow one to create maximally entangled Bell
states, as well as three qubit Greenberger-Horne-Zeilinger and W states. In
particular, we point out that some of the target states are the eigenstates of
the initial bare system. Due to this, one can create entangled states by means
of pulse area and adiabatic techniques, when starting from a separable
(non-entangled) ground state. On the other hand, for target states, not present
initially in the eigensystem of the model, we apply the robust stimulated Raman
adiabatic passage and pulse techniques, that create desired coherent
superpositions of non-entangled eigenstates.Comment: 9 pages, 7 figures. Updated version for publicatio
Image retrieval : a first step for a human centered approach
International audienceImage indexing using content analysis is known as a difficult task, involving the vision research domain. Using these tools in the context of a retrieval system is generally frustrating for users, due to a lack of interfaces development, and to the difficulty for users to understand the low-level features managed by the system. We propose in this paper a general point of view for introducing a link between such systems and potential users. This includes image features based on visual perception models, a relevance feedback model, and a graphical interface to express the information need through user-system interaction
A simple and efficient feedback control strategy for wastewater denitrification
Due to severe mathematical modeling and calibration difficulties open-loop
feedforward control is mainly employed today for wastewater denitrification,
which is a key ecological issue. In order to improve the resulting poor
performances a new model-free control setting and its corresponding
"intelligent" controller are introduced. The pitfall of regulating two output
variables via a single input variable is overcome by introducing also an
open-loop knowledge-based control deduced from the plant behavior. Several
convincing computer simulations are presented and discussed.Comment: IFAC 2017 World Congress, Toulouse, Franc
Optimal control and ultimate bounds of 1:2 nonlinear quantum systems
Using optimal control, we establish and link the ultimate bounds in time
(referred to as quantum speed limit) and energy of two- and three-level quantum
nonlinear systems which feature 1:2 resonance. Despite the unreachable complete
inversion, by using the Pontryagin maximum principle, we determine the optimal
time, pulse area, or energy, for a given arbitrary accuracy. We show that the
third-order Kerr terms can be absorbed in the detuning in order to lock the
dynamics to the resonance. In the two-level problem, we determine the
non-linear counterpart of the optimal -pulse inversion for a given
accuracy. In the three-level problem, we obtain an intuitive pulse sequence
similar to the linear counterpart but with different shapes. We prove the
(slow) logarithmic increasing of the optimal time as a function of the
accuracy
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