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1
Content available remote

Average entanglement of spin 1 and 1/2 pair

100%
Zhu G.-Q.
Open Physics
|
2009
|
vol. 7
|
issue 1
135-140
EN
We study the entanglement features of the ground state of a system composed of spin 1 and 1/2 parts. In the light of the ground state degeneracy, the notion of average entanglement is used to measure the entanglement of the Hilbert subspace. The entanglement properties of both a general superposition as well as the mixture of the degenerate ground states are discussed by means of average entanglement and the negativity respectively.
2
Content available remote

A hierarchy of Hamilton operators and entanglement

80%
Steeb W.-H., Hardy Y.
Open Physics
|
2009
|
vol. 7
|
issue 4
854-859
EN
We consider a hierarchy of Hamilton operators Ĥ N in finite dimensional Hilbert spaces $$ \mathbb{C}^{2^N } $$. We show that the eigenstates of Ĥ N are fully entangled for N even. We also calculate the unitary operator U N(t) = exp(-Ĥ N t/ħ) for the time evolution and show that unentangled states can be transformed into entangled states using this operator. We also investigate energy level crossing for this hierarchy of Hamilton operators.
3
Content available remote

Quantum discord between two moving two-level atoms

80%
Hu Y.-H., Fang M.-F.
Open Physics
|
2012
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vol. 10
|
issue 1
145-150
EN
Considering a double JC model, this paper investigates the quantum discord dynamics of two isolated moving two-level atoms each interacting with a single-mode thermal cavity field, and studies the effect of the atomic motion and the field-mode structure on quantumdiscord. The results show that, on the one hand the quantum discord evolves periodically with time and the periods are affected by the atomic motion and the field-mode structure; on the other hand, the quantum discord still can capture the quantum correlation between the two atoms when the entanglement is zero. It is interesting to note that the quantum discord can be effectively preserved by controlling the field-mode structure parameter
4
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The influence of spontaneously generated coherence on atom-photon entanglement in a Λ-type system with an incoherent pump

80%
Yang X., Yan D., Bao Q., Zhang Y., Cui C.
Open Physics
|
2014
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vol. 12
|
issue 12
813-821
EN
Owing to interference induced by spontaneous emission, the density-matrix equations in a three-level Λ-type system have an additional coherence term, which plays a critical role in modulating the inversionless gain and electromagnetically induced transparency effect. In addition, it is shown that spontaneously generated coherence (SGC) has an effect on the entanglement between an atom and a photon of the coupling laser field by calculating the degree of entanglement (DEM) of the atomic system. In this paper, we investigate the influence of the SGC effect on atom-photon entanglement in a Λ-type system, which generally remains a high entangled state. When an incoherent pump source is introduced, we find that the SGC effect could exert considerable influence on the atom reduced entropy under certain conditions for both transient and steady states. More interestingly, such an incoherent pump field could actively affect the short-time dynamic behaviors of the transient quantum entangled state at a certain range of pump rate as a typical coherent case.
5
Content available remote

Using simple elastic bands to explain quantum mechanics: a conceptual review of two of Aerts’ machine-models

70%
Sassoli de Bianchi M.
Open Physics
|
2013
|
vol. 11
|
issue 2
147-161
EN
From the beginning of his research, the Belgian physicist Diederik Aerts has shown great creativity in inventing a number of concrete machine-models that have played an important role in the development of general mathematical and conceptual formalisms for the description of the physical reality. These models can also be used to demystify much of the strangeness in the behavior of quantum entities, by allowing to have a peek at what’s going on behind the “quantum scenes,” during a measurement. In this author’s view, the importance of these machine-models, and of the approaches they have originated, have been so far seriously underappreciated by the physics community, despite their success in clarifying many challenges of quantum physics. To fill this gap, and encourage a greater number of researchers to take cognizance of the important work of so-called Geneva-Brussels school, we describe and analyze in this paper two of Aerts’ historical machine-models, whose operations are based on simple breakable elastic bands. The first one, called the spin quantum-machine, is able to replicate the quantum probabilities associated with the spin measurement of a spin-1/2 entity. The second one, called the connected vessels of water model (of which we shall present here an alternative version based on elastics) is able to violate Bell’s inequality, as coincidence measurements on entangled states can do.
6
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Entanglement in the second quantization formalism

61%
Vedral V.
Open Physics
|
2003
|
vol. 1
|
issue 2
289-306
EN
We study properties of entangled systems in the (mainly non-relativistic) second quantization formalism. This is then applied to interacting and non-interacting bosons and fermions and the differences between the two are discussed. We present a general formalism to show how entanglement changes with the change of modes of the system. This is illustrated with examples such as the Bose condensation and the Unruh effect. It is then shown that a non-interacting collection of fermions at zero temperature can be entangled in spin, providing that their distances do not exceed the inverse Fermi wavenumber. Beyond this distance all bipartite entanglement vanishes, although classical correlations still persist. We compute the entanglement of formation as well as the mutual information for two spin-correlated electrons as a function of their distance. The analogous, non-interacting collection of bosons displays no entanglement in the internal degrees of freedom. We show how to generalize our analysis of the entanglement in the internal degrees of freedom to an arbitrary number of particles.
7
Content available remote

Dynamics of two quantum entangled particles interacting with a potential barrier in an EPR experiment

51%
Petrillo V., Alberti G., Celardo L., Cerutti F., Franchi S., Mariani V.
Open Physics
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2006
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vol. 4
|
issue 2
196-209
EN
The effect of a position measurement on one component of a two-particle wave packet in a regularized space-momentum entangled state is analyzed. The wave packet interacts in the physical space with a potential barrier. When a position or momentum measurement is performed on one particle, a consequent strong modification of the dynamics of the other particle occurs.
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