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1
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Disentanglement and Black Holes: Information Problem

100%
Radosz A., Gusin P., Roszak K.
Acta Physica Polonica A
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2017
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vol. 132
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issue 1
132-134
EN
One of the possible ways of formulation of an information loss paradox refers to an entanglement of the two particles created in a vicinity of an event horizon. Evolution of the entangled particles and an interaction with their own environments should lead to a decay of the entanglement. However obvious, such a perspective appears to be too naive in this case.
2
Content available remote

Mean spin direction and spin squeezing in superpositions of spin coherent states

100%
Yan D., Wang X., Song L., Zong Z.
Open Physics
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2007
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vol. 5
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issue 3
367-376
EN
We consider the mean spin direction (MSD) of superpositions of two spin coherent states (SCS) | ± μ〉, and superpositions of | μ〉 and | μ*〉 with a relative phase. We find that the azimuthal angle exhibits a π transition for both states when we vary the relative phase. The spin squeezing of the states, and the bosonic counterpart of the mean spin direction are also discussed.
3
Content available remote

A hierarchy of Hamilton operators and entanglement

76%
Steeb W.-H., Hardy Y.
Open Physics
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2009
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vol. 7
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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.
4
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System Size Dependence of Entanglement in Quantum One-Dimensional Models

76%
Jakubczyk D., Jakubczyk P.
Acta Physica Polonica A
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2017
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vol. 132
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issue 1
158-160
EN
We show that entanglement in one-dimensional spin and electron systems, with one excitation, depends only on the system size and has very simple form in both multipartite and bipartite case. Regarding the multipartite case, we present very simple expressions for global entanglement and N-concurrence, and show that they are mutually related. In the bipartite case, we give expressions for I-concurrence and negativity, and show that they are also dependent on each other.
5
Content available remote

Average entanglement of spin 1 and 1/2 pair

76%
Zhu G.-Q.
Open Physics
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2009
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vol. 7
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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.
6
Content available remote

Entanglement conditions for four-mode states via the uncertainty relations in conjunction with partial transposition

76%
Song L., Wang X., Yan D., Li Y.
Open Physics
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2008
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vol. 6
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issue 2
199-204
EN
From the Heisenberg uncertainty relation in conjunction with partial transposition, we derive a class of inequalities for detecting entanglements in four-mode states. The sufficient conditions for bipartite entangled states are presented. We also discuss the generalization of the entanglement conditions via the Schrödinger-Robertson indeterminacy relation, which are in general stronger than those based on the Heisenberg uncertainty relation.
7
Content available remote

On the role of entanglement in Schrödinger’s cat paradox

64%
Rinner S., Werner E.
Open Physics
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2008
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vol. 6
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issue 1
178-183
EN
In this paper we re-investigate the core of Schrödinger’s “cat paradox”. We argue that one has to distinguish clearly between superpositions of macroscopic cat states |☺〉 + |☹〉 and superpositions of entangled states |☺, ↑〉 + |☹, ↓〉 which comprise both the state of the cat (☺=alive, ☹=dead) and the radioactive substance (↑=not decayed, ↓=decayed). It is shown, that in the case of the cat experiment recourse to decoherence or other mechanisms is not necessary in order to explain the absence of macroscopic superpositions. Additionally, we present modified versions of two quantum optical experiments as experimenta crucis. Applied rigorously, quantum mechanical formalism reduces the problem to a mere pseudo-paradox.
8
Content available remote

Entanglement Conditions Involving Intensity Correlations of Optical Fields: the Case of Multi-Port Interferometry

64%
Ryu J., Marciniak M., Wieśniak M., Kaszlikowski D., Żukowski M.
Acta Physica Polonica A
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2017
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vol. 132
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issue 6
1713-1718
EN
Normalized quantum Stokes operators introduced in Phys. Rev. A 95, 042113 (2017) enable one to better observe non-classical correlations of entangled states of optical fields with undefined photon numbers. For a given run of an experiment the new quantum Stokes operators are defined by the differences of the measured intensities (or photon numbers) at the exits of a polarizer divided by their sum. It is this ratio that is to be averaged, and not the numerator and the denominator separately, as it is in the conventional approach. The new approach allows to construct more robust entanglement indicators against photon-loss noise, which can detect entangled optical states in situations in which witnesses using standard Stokes operators fail. Here we show an extension of this approach beyond phenomena linked with polarization. We discuss EPR-like experiments involving correlations produced by optical beams in a multi-mode bright squeezed vacuum state. EPR-inspired entanglement conditions for all prime numbers of modes are presented. The conditions are much more resistant to noise due to photon loss than similar ones which employ standard Glauber-like intensity, correlations.
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