Entanglement and nonclassicality: A mutual impression

Gholipour, Hossein; Shähandeh, Farid

doi:10.1103/physreva.93.062318

Cited by 23 publications

(20 citation statements)

References 33 publications

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“…pointed that efficient quantum computation is possible to be realized by using only beam-splitters, phase shifters, single photon sources and photo-detectors35. Although beam-splitters are linear optical devices, they can generate quantum entanglement36373839.…”

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confidence: 99%

Gaussian entanglement generation from coherence using beam-splitters

Wang

et al. 2016

Sci Rep

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The generation and quantification of quantum entanglement is crucial for quantum information processing. Here we study the transition of Gaussian correlation under the effect of linear optical beam-splitters. We find the single-mode Gaussian coherence acts as the resource in generating Gaussian entanglement for two squeezed states as the input states. With the help of consecutive beam-splitters, single-mode coherence and quantum entanglement can be converted to each other. Our results reveal that by using finite number of beam-splitters, it is possible to extract all the entanglement from the single-mode coherence even if the entanglement is wiped out before each beam-splitter.

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confidence: 99%

Gaussian entanglement generation from coherence using beam-splitters

Wang

et al. 2016

Sci Rep

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“…On the other hand, however, quantum correlations in quantum optics lack such a nonlocal operational justification, i.e., there is no particular quantum information protocol which exploits phase-space nonclassicality to outperform a classical counterpart protocol. Although, it has been recently shown that such nonclassicalities provide either necessary or sufficient resources for entanglement generation [11][12][13], which then can be used in various protocols.…”

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confidence: 99%

Quantum Correlations in Nonlocal Boson Sampling

2017

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Determination of the quantum nature of correlations between two spatially separated systems plays a crucial role in quantum information science. Of particular interest is the questions of if and how these correlations enable quantum information protocols to be more powerful. Here, we report on a distributed quantum computation protocol in which the input and output quantum states are considered to be classically correlated in quantum informatics. Nevertheless, we show that the correlations between the outcomes of the measurements on the output state cannot be efficiently simulated using classical algorithms. Crucially, at the same time, local measurement outcomes can be efficiently simulated on classical computers. We show that the only known classicality criterion violated by the input and output states in our protocol is the one used in quantum optics, namely, phase-space nonclassicality. As a result, we argue that the global phase-space nonclassicality inherent within the output state of our protocol represents true quantum correlations.Introduction.-Correlations play an undeniable role in our understanding of the physical world. In our macroscopic classical description of commonplace phenomena, classical physics and classical information theory are in perfect agreement in characterization and quantification of correlated events. At a microscopic level, where quantum theory is our best candidate for explaining phenomena, however, the situation is different. Our informational inspections of a quantum world, i.e., quantum information theory, is based on our intuition from classical information theory and classical probability theory, mostly the notion of quantum entropy [1, 2]. However, a discrepancy emerges when physical constraints are taken into account to distinguish between quantum physics and classical physics, hence splitting quantum information approach to correlations from that of quantum optics.In quantum optics it is common to study nonclassical features of bosonic systems in a quantum analogue of the classical phase space [3]. While in a classical statistical theory in phase-space the state of the system is represented by a probability distribution, the quantum phase-space distributions can have negative regions, and hence, fail to be legitimate probability distributions [4]. The negativities are thus considered as nonclassicality signatures. Within multipartite quantum states, the phase-space nonclassicality is tempted to be interpreted as quantum correlations, due to the fact that in a classical description of the joint system no such effects are present [5,6].The sharpest contrast between the definition of quantum correlations in quantum information science and that of quantum optics has been demonstrated very recently by Ferraro and Paris [7]. They showed that the two definitions from quantum information and quantum optics are maximally inequivalent, meaning that every quantum state which is classically correlated with respect to the quantum information definition of quantum correlations is nece...

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“…Indeed many strategies can be taken to implement SEW depending on M A and M B , while taking care that the obtained witness contains an entangled eigenspace [8,9]. To show that this is not a requirement of UEW, we give the following simple-to-construct example of a UEW strategy to detect a range of entangled states.…”

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confidence: 99%

“…This simplification, however, comes at a cost: first, different entangled states in general require different EWs to be detected; second, not every EW can be practically realized, i.e., can be decomposed into operators corresponding to available local measurement devices (See also Refs. [7][8][9] for examples of the reverse procedure: constructing EWs from local observables); third, when such a decomposition is possible, it might require multiple measurement devices (with multiple settings) to be implemented; and fourth, witnessing bounds can be elusive in the presence of experimental imperfections. Consequently, the goal is to construct EWs that have a simple decomposition and, at the same time, detect a large set of entangled states.…”

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confidence: 99%

Ultrafine Entanglement Witnessing

et al. 2017

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Entanglement witnesses are invaluable for efficient quantum entanglement certification without the need for expensive quantum state tomography. Yet, standard entanglement witnessing requires multiple measurements and its bounds can be elusive as a result of experimental imperfections. Here, we introduce and demonstrate a novel procedure for entanglement detection which simply and seamlessly improves any standard witnessing procedure by using additional available information to tighten the witnessing bounds. Moreover, by relaxing the requirements on the witness operators, our method removes the general need for the difficult task of witness decomposition into local observables. We experimentally demonstrate entanglement detection with our approach using a separable test operator and a simple fixed measurement device for each agent. Finally, we show that the method can be generalized to higher-dimensional and multipartite cases with a complexity that scales linearly with the number of parties. DOI: 10.1103/PhysRevLett.118.110502 Quantum entanglement provides many advantages beyond classical limits, including quantum communication, computation, and information processing [1,2]. Yet, determining whether a given quantum state is entangled or not is a theoretically and experimentally challenging task [3,4]. In particular, the ideal approach of reconstructing the full quantum state via quantum tomography is practically infeasible for all but the smallest systems.An elegant solution to this problem, known as entanglement witnessing, relies on the geometry of the set of nonentangled (separable) quantum states [2,[5][6][7]. Since these states form a convex set, it is always possible to find a hyperplane such that a given entangled state lies on one side of the hyperplane, while all separable states are on the other side, see Fig. 1. This hyperplane is a so-called entanglement witness (EW) and corresponds to a joint observable that has a bounded expectation value over all separable quantum states. Any quantum state that produces a value beyond the bound must be entangled. This simplification, however, comes at a cost: first, different entangled states in general require different EWs to be detected; second, not every EW can be practically realized, i.e., can be decomposed into operators corresponding to available local measurement devices (See also Refs. [7][8][9] for examples of the reverse procedure: constructing EWs from local observables); third, when such a decomposition is possible, it might require multiple measurement devices (with multiple settings) to be implemented; and fourth, witnessing bounds can be elusive in the presence of experimental imperfections. Consequently, the goal is to construct EWs that have a simple decomposition and, at the same time, detect a large set of entangled states.There are three main techniques to improve EWs. First, adding nonlinear terms to the original witness operator [10]; second, using collective measurements of EWs on multiple copies of the quantum state [11]; and third, op...

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Entanglement and nonclassicality: A mutual impression

Cited by 23 publications

References 33 publications

Gaussian entanglement generation from coherence using beam-splitters

Gaussian entanglement generation from coherence using beam-splitters

Quantum Correlations in Nonlocal Boson Sampling

Ultrafine Entanglement Witnessing

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