Observing the operational significance of discord consumption

Gu, Mile; Chrzanowski, Helen M.; Assad, Syed M.; Symul, Thomas; Modi, Kavan; Ralph, T. C.; Vedral, Vlatko; Lam, Ping Koy

doi:10.1038/nphys2376

Cited by 225 publications

(236 citation statements)

References 28 publications

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“…In addition, quantum discord seems to have a relation with noisy teleportation, entanglement distillation and quantum state merging [6]. Some experimental effort to check quantum discord are under progress [7,8].…”

Section: Introductionmentioning

confidence: 99%

Revisiting Quantum Discord for Two-Qubit X States: The Error Bound to an Analytical Formula

et al. 2015

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Section: Introductionmentioning

confidence: 99%

Revisiting Quantum Discord for Two-Qubit X States: The Error Bound to an Analytical Formula

et al. 2015

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“…Since quantum discord is related to the noncommutativity of observables, it is often expected that modulation in both conjugate quadratures is required to see quantum behavior. In contrast to all previous discord experiments [20,[24][25][26], to generate discord we modulate the input coherent state only in one of the conjugate quadratures,x in , keepingp in at the coherent-state level, V p = 2 p 2 in = 1, wherex in (p in ) is the x(p) quadrature of mode "in." The local loss is realized by variable attenuation in mode B denoted asˆ in Fig.…”

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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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“…Introduction -Homodyne detection (HD) is an effective tool to characterize the quantum state of light in either the time [1][2][3][4][5][6][7][8] or the frequency [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] domain. In a spectral homodyne detector, the signal under investigation interferes at a balanced beam splitter with a local oscillator (LO) with frequency ω 0 .…”

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Full quantum state reconstruction of symmetric two-mode squeezed thermal states via spectral homodyne detection and a state-balancing detector

et al. 2016

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We suggest and demonstrate a scheme to reconstruct the symmetric two-mode squeezed thermal states of spectral sideband modes from an optical parametric oscillator. The method is based on a single homodyne detector and active stabilization of the cavity. The measurement scheme have been successfully tested on different two-mode squeezed thermal states, ranging from uncorrelated coherent states to entangled states.PACS numbers: 03.65. Wj, 42.50.Lc, 42.50.Dv Introduction -Homodyne detection (HD) is an effective tool to characterize the quantum state of light in either the time [1][2][3][4][5][6][7][8] or the frequency [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] domain. In a spectral homodyne detector, the signal under investigation interferes at a balanced beam splitter with a local oscillator (LO) with frequency ω 0 . The two outputs undergo a photodetection process and their photocurrents are combined leading to a photocurrent continuously varying in time. The information about the spectral field modes at frequencies ω 0 ± Ω (sidebands) is then retrieved by electronically mixing the photocurrent with a reference signal with frequency Ω and phase Ψ. Upon varying the phase θ of the LO, we may access different field quadratures, whereas the phase Ψ can be adjusted to select the symmetric S or antisymmetric A balanced combinations of the upper and lower sideband modes.

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Observing the operational significance of discord consumption

Cited by 225 publications

References 28 publications

Revisiting Quantum Discord for Two-Qubit X States: The Error Bound to an Analytical Formula

Revisiting Quantum Discord for Two-Qubit X States: The Error Bound to an Analytical Formula

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

Full quantum state reconstruction of symmetric two-mode squeezed thermal states via spectral homodyne detection and a state-balancing detector

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