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Chakhmakhchyan L.,Laboratory Interdisciplinaire Carnot de Bourgogne | Chakhmakhchyan L.,Institute for Physical Research | Chakhmakhchyan L.,Ai Alikhanyan National Science Laboratory | Guerin S.,Laboratory Interdisciplinaire Carnot de Bourgogne | And 2 more authors.
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2013

We adopt the beam-splitter model for losses to analyze the performance of a recent compact continuous-variable entanglement distillation protocol 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 mc of phonon subtraction attempts from the matter modes of the quantum memory. If the initial state is not de-Gaussified within mc attempts, the protocol should be restarted to obtain any entanglement increase. Moreover, the condition m c>1 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. © 2013 American Physical Society.

Chakhmakhchyan L.,Ai Alikhanyan National Science Laboratory | Chakhmakhchyan L.,Laboratory Interdisciplinaire Carnot de Bourgogne | Chakhmakhchyan L.,Institute for Physical Research | Shepelyansky D.,French National Center for Scientific Research
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2013

We consider a PageRank model of opinion formation on Ulam networks, generated by the intermittency map and the typical Chirikov map. The Ulam networks generated by these maps have certain similarities with such scale-free networks as the World Wide Web (WWW), showing an algebraic decay of the PageRank probability. We find that the opinion formation process on Ulam networks has certain similarities but also distinct features comparing to the WWW. We attribute these distinctions to internal differences in network structure of the Ulam and WWW networks. We also analyze the process of opinion formation in the frame of generalized Sznajd model which protects opinion of small communities. © 2013 Elsevier B.V.

Chakhmakhchyan L.,University of Burgundy | Chakhmakhchyan L.,Institute for Physical Research | Chakhmakhchyan L.,Ai Alikhanyan National Science Laboratory | Leroy C.,University of Burgundy | And 2 more authors.
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2014

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 (nonentangled) 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 π pulse techniques, that create desired coherent superpositions of nonentangled eigenstates. © 2014 American Physical Society.

Ananikian N.S.,A i Alikhanyan National Science Laboratory | Ananikian N.S.,Federal University of Lavras | Ananikyan L.N.,A i Alikhanyan National Science Laboratory | Chakhmakhchyan L.A.,A i Alikhanyan National Science Laboratory | And 3 more authors.
Journal of Physics Condensed Matter | Year: 2012

The entanglement quantum properties of a spin-1/2 IsingHeisenberg model on a symmetrical diamond chain were analyzed. Due to the separable nature of the Ising-type exchange interactions between neighboring Heisenberg dimers, calculation of the entanglement can be performed exactly for each individual dimer. Pairwise thermal entanglement was studied in terms of the isotropic IsingHeisenberg model and analytical expressions for the concurrence (as a measure of bipartite entanglement) were obtained. The effects of external magnetic field H and next-nearest neighbor interaction J m between nodal Ising sites were considered. The ground state structure and entanglement properties of the system were studied in a wide range of coupling constant values. Various regimes with different values of ground state entanglement were revealed, depending on the relation between competing interaction strengths. Finally, some novel effects, such as the two-peak behavior of concurrence versus temperature and coexistence of phases with different values of magnetic entanglement, were observed. © 2012 IOP Publishing Ltd.

Chakhmakhchyan L.,Ai Alikhanyan National Science Laboratory | Chakhmakhchyan L.,Institute for Physical Research | Ananikian N.,Ai Alikhanyan National Science Laboratory | Ananikyan L.,Ai Alikhanyan National Science Laboratory | Burdik C.,Czech Technical University
Journal of Physics: Conference Series | Year: 2012

The entanglement thermal (equilibrium) properties in spin-1/2 Ising-Heisenberg model on an ideal diamond chain is analyzed. Due to the classical character of Ising-type exchange interactions between two neighboring antiferromagnetic Heisenberg dimers, the calculation of quantum entanglement (by tracing out Ising spins) can be performed for each of the dimers separately. The concurrence, as a measure of entanglement is obtained and different regimes depending on the values of exchange interactions are revealed. The effects of the magnetic field are incorporated and critical temperatures corresponding to the vanishing or arising of entanglement are considered.

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