Experimental Distribution of Entanglement with Separable Carriers

Fedrizzi, Alessandro; Zuppardo, Margherita; Gillett, Geoff; Broome, Matthew A.; Almeida, M. P.; Paternostro, Mauro; White, A. G.; Paterek, Tomasz

doi:10.1103/physrevlett.111.230504

Cited by 71 publications

(91 citation statements)

References 28 publications

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“…Finally, a number of experiments have successfully demonstrated entanglement distribution with separable states in discrete and continuous variable setups [226,227,228].…”

Section: Entanglement Distributionmentioning

confidence: 99%

Measures and applications of quantum correlations

Adesso¹,

Bromley²,

Cianciaruso³

2016

J. Phys. A: Math. Theor.

386

416

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Abstract. Quantum information theory is built upon the realisation that quantum resources like coherence and entanglement can be exploited for novel or enhanced ways of transmitting and manipulating information, such as quantum cryptography, teleportation, and quantum computing. We now know that there is potentially much more than entanglement behind the power of quantum information processing. There exist more general forms of non-classical correlations, stemming from fundamental principles such as the necessary disturbance induced by a local measurement, or the persistence of quantum coherence in all possible local bases. These signatures can be identified and are resilient in almost all quantum states, and have been linked to the enhanced performance of certain quantum protocols over classical ones in noisy conditions. Their presence represents, among other things, one of the most essential manifestations of quantumness in cooperative systems, from the subatomic to the macroscopic domain. In this work we give an overview of the current quest for a proper understanding and characterisation of the frontier between classical and quantum correlations in composite states. We focus on various approaches to define and quantify general quantum correlations, based on different yet interlinked physical perspectives, and comment on the operational significance of the ensuing measures for quantum technology tasks such as information encoding, distribution, discrimination and metrology. We then provide a broader outlook of a few applications in which quantumness beyond entanglement looks fit to play a key role.

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“…Finally, a number of experiments have successfully demonstrated entanglement distribution with separable states in discrete and continuous variable setups [226,227,228].…”

Section: Entanglement Distributionmentioning

confidence: 99%

Measures and applications of quantum correlations

Adesso¹,

Bromley²,

Cianciaruso³

2016

J. Phys. A: Math. Theor.

386

416

View full text Add to dashboard Cite

show abstract

“…To place these results in context, consider more involved and counterintuitive experimental protocols, that is, distribution of entanglement by separable states [31,[39][40][41] and entanglement activation from discord [42]. These protocols begin with multipartite discordant but fully separable states.…”

mentioning

confidence: 99%

Quantum nature of Gaussian discord: Experimental evidence and role of system-environment correlations

et al. 2015

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We provide experimental evidence of quantum features in bipartite states classified as entirely classical according to a conventional criterion based on the Glauber P function but possessing nonzero Gaussian quantum discord. Their quantum nature is experimentally revealed by acting locally on one part of the discordant state. We experimentally verify and investigate the effect of discord increase under the action of local loss and link it to the entanglement with the environment. Adding an environmental system purifying the state, we unveil the flow of quantum correlations within a global pure system using the Koashi-Winter inequality. For a discordant state generated by splitting a state in which the initial squeezing is destroyed by random displacements, we demonstrate the recovery of entanglement highlighting the role of system-environment correlations. As quantum information science develops towards quantum information technology, the question of the efficient use and optimization of resources becomes a burning issue. So far, quantum information processing (QIP) has been mostly thought of as entanglement-enabled technology. Quantum cryptography is an exception, but even there the so-called effective entanglement between the parties plays a decisive role [1,2]. With the advent of new quantum computation paradigms [3] interest in more generic and even nonentangled QIP resources has emerged [4]. Unlike entanglement, the new resources, commonly dubbed as quantum correlations, reside in all states which do not diagonalize in any local product basis. Entanglement and quantum correlations are equivalent notions only for pure states. Quantumness of correlations in separable states is fundamentally related to the noncommutativity of observables, nonorthogonality of states, and properties of quantum measurements, whereas entanglement can be seen as a consequence of the quantum superposition principle. Correlated mixed states are a lucid illustration of the fact that the quantum-classical divide is actually purpose-oriented and that such states, long considered unsuitable for QIP, may become a robust and efficient quantum tool.In what follows, we will use quantum discord [5] for quantification of quantum correlations. For two systems A and B, quantum discord is defined as the difference,between quantum mutual information I(AB) = S(A) + S(B) − S(AB) encompassing all correlations present in the system, and the one-way classical correlation, which is operationally related to the amount of perfect classical correlations which can be extracted from the system [6]. Here, S is the von Neumann entropy of the respective state, H {ˆ i } (A|B) is the conditional entropy with measurement on B, and the infimum is taken over all possible measurements {ˆ i }.In this Rapid Communication, we focus on bipartite mixed Gaussian states relevant in the context of continuousvariable quantum information [7]. The respective correlation quantifier is then Gaussian quantum discord [8,9] defined by Eq. (1), where the minimization in J ← (AB) is r...

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“…[27]: she sequentially prepares photons in one of the states {|H H ,|V V ,|DD ,|AA ,|RR ,|LL }, where |D ,|A = (|H ± |V )/ √ 2 and |R ,|L = (|H ± i|V )/ √ 2, and applies one of the four encodings k. Bob's Bell-state measurement sums up over all components of Alice's state to extract the final measurement outcomes. The experimental mutual information rate is given by…”

Section: Experiments and Resultsmentioning

confidence: 99%

Entanglement-free certification of entangling gates

Almeida

Fedrizzi

et al. 2014

Phys. Rev. A

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Not all quantum protocols require entanglement to outperform their classical alternatives. The nonclassical correlations that lead to a quantum advantage are conjectured to be captured by quantum discord. Here we demonstrate that discord has an immediate practical application: it allows a client who lacks the ability to generate entanglement or conduct quantum measurements to certify whether an untrusted party has entangling gates. We implement our protocol in the discrete-variable regime with photonic qubits and show its success in the presence of high levels of noise and imperfect gate operations. Our technique offers a practical method to test claims of quantum processing and to benchmark entangling operations for physical architectures in which only highly mixed states are available.

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Experimental Distribution of Entanglement with Separable Carriers

Cited by 71 publications

References 28 publications

Measures and applications of quantum correlations

Measures and applications of quantum correlations

Quantum nature of Gaussian discord: Experimental evidence and role of system-environment correlations

Entanglement-free certification of entangling gates

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