Quantum Communication with Continuous Variables

Loock, Peter van

doi:10.1002/1521-3978(200212)50:12<1177::aid-prop1177>3.0.co;2-t

Cited by 51 publications

(78 citation statements)

References 175 publications

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“…Although several alternative formalisms are available for the description of the B-K CV teleportation protocol [35,36,37,38,39,40], the characteristic function representation proves to be particularly convenient when considering the nonideal case and non-Gaussian resources. The description of nonideal teleportation re- In the first step, the input mode is mixed by Alice with one of the two beams (modes) of the entangled resource; the ensuing state is then subject to a realistic Bell measurement.…”

Section: Nonideal CV Teleportation Protocol In the Characteristicmentioning

confidence: 99%

Realistic continuous-variable quantum teleportation with non-Gaussian resources

2010

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We present a comprehensive investigation of nonideal continuous-variable quantum teleportation implemented with entangled non-Gaussian resources. We discuss in a unified framework the main decoherence mechanisms, including imperfect Bell measurements and propagation of optical fields in lossy fibers, applying the formalism of the characteristic function. By exploiting appropriate displacement strategies, we compute analytically the success probability of teleportation for input coherent states, and two classes of non-Gaussian entangled resources: Two-mode squeezed Bell-like states (that include as particular cases photon-added and photon-subtracted de-Gaussified states), and two-mode squeezed cat-like states. We discuss the optimization procedure on the free parameters of the non-Gaussian resources at fixed values of the squeezing and of the experimental quantities determining the inefficiencies of the non-ideal protocol. It is found that non-Gaussian resources enhance significantly the efficiency of teleportation and are more robust against decoherence than the corresponding Gaussian ones. Partial information on the alphabet of input states allows further significant improvement in the performance of the nonideal teleportation protocol.

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Section: Nonideal CV Teleportation Protocol In the Characteristicmentioning

confidence: 99%

Realistic continuous-variable quantum teleportation with non-Gaussian resources

2010

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“…As is known, the gain g = (e 4r − 1)/(e 4r + 1/2) yields the optimal fidelity for the CV GHZ states, with the classical fidelity 1/2 achieved even in a zerosqueezing limit r → 0 [57]. When maximized over g, the CV GHZ states with photon subtraction on two modes still achieves better fidelities over the CV GHZ states and it also approaches the classical fidelity 1/2 as r → 0.…”

Section: B Optimal Gainmentioning

confidence: 99%

“…Charlie obtains the output state after displacing his mode by the amount of √ 2(x u + ip v ) + igp 2 , where g is a gain factor that can be adjusted to give an optimal fidelity. Without the information on p 2 , the output fidelity may go below the classical bound as the squeezing parameter r increases [57]. A high fidelity that can be achieved only with other remaining party's help can be regarded as an evidence of multipartite entanglement.…”

Section: Fidelity Of the Teleportation Network Protocolmentioning

confidence: 99%

“…This is not only because there are few protocols exploiting multipartite nature of a system but also because it is difficult to characterize multipartite correlations in general, especially, for non-Gaussian states in CV quantum information regime [55]. Here, extending two-mode systems into multipartite systems, we investigate the effects of photon operations on quantum correlations of a class of multipartite continuous variable systems, the CV GHZ states introduced by van Loock and Braunstein [56][57][58]. Quantum nonlocality already has been investigated on this class and the CV GHZ states have shown violations of local realism [59,60].…”

Section: Introductionmentioning

confidence: 99%

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Enhanced multipartite quantum correlation by non-Gaussian operations

Kim

Nha

2013

Phys. Rev. A

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We study how conditional photon operations can affect multipartite quantum correlations, specifically nonlocality and entanglement, of the continuous variable GHZ states. We find that the violation of the Mermin-Klyshko inequality revealing the multipartite nonlocality can be made stronger with photon subtraction applied on each mode of the original GHZ states, particularly in a weak squeezing regime. Photon addition applied on local modes also turns out to enhance the degree of multipartite nonlocality in a broad range of parameters. We further investigate the effects of the photon operations on the degree of multipartite entanglement by looking into the Gaussian tangle, the fidelity of teleportation network, and the quadrature correlations. We find that photon subtraction applied on two modes enhances those entanglement characteristics in a practical squeezing regime while there is no improvement made by photon addition.

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“…However, due to the finite squeezing of both initial entanglement sources, the final entanglement after swapping in the CV scheme is inevitably degraded by excess noise. In fact, the entanglement drops exponentially [17,18] and in practice, CV entanglement swapping can always be replaced by a direct transmission through a lossy channel [19]. Moreover, purification techniques for this type of degraded entanglement are not so advanced at present [20,21].…”

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confidence: 99%

Entanglement Swapping between Discrete and Continuous Variables

et al. 2015

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We experimentally realize "hybrid" entanglement swapping between discrete-variable (DV) and continuous-variable (CV) optical systems. DV two-mode entanglement as obtainable from a single photon split at a beam splitter is robustly transferred by means of efficient CV entanglement and operations, using sources of squeezed light and homodyne detections. The DV entanglement after the swapping is verified without post-selection by the logarithmic negativity of up to 0.28±0.01. Furthermore, our analysis shows that the optimally transferred state can be post-selected into a highly entangled state that violates a Clauser-Horne-Shimony-Holt inequality by more than 4 standard deviations, and thus it may serve as a resource for quantum teleportation and quantum cryptography.PACS numbers: 03.65. Ud, 03.67.Hk, 42.50Ex Quantum entanglement can be created between two distant quantum systems that have never directly interacted. This effect, called entanglement swapping [1][2][3][4][5][6][7][8], is a building block for quantum communication and computation [9][10][11][12]. It was originally proposed and demonstrated for discrete-variable (DV) optical systems [1][2][3][4]. The protocol starts with two entangled pairs, A-B and C-D, each represented either by twin photons or by a single photon split into two distinct modes [ Fig. 1 (a)].A joint projective measurement of B and C onto one of the four two-qubit Bell states then leads to an entangled state for A and D, even though A and D never directly interact with each other. Entanglement swapping can also be interpreted as the transfer of one half of an entangled state, either from B to D or from C to A, by quantum teleportation [13]. It is a key element for quantum networking [9], quantum computing [10], quantum cryptography [14], and especially long-distance quantum communication by means of quantum repeaters [11,12]. However, in this DV setting solely based upon single photons, due to the heralded conditional entangled-state generation and the probabilistic linear-optics Bell-state measurement (BSM), successful entanglement swapping events occur very rarely. As a result, in a quantum repeater for example, long-distance entangled-pair creation rates would be correspondingly low and requirements on the coherence times of the local quantum memories at each repeater station impractically high. In addition, the observation and verification of the final entanglement between A and D in the DV scheme typically requires postselection.Entanglement swapping was later extended to continuous-variable (CV) systems [15,16], where the pairs A-B and C-D each correspond to the two modes of a two-mode squeezed, quadrature-entangled state [5,6] [ Fig. 1(b)]. Since such entangled states are available on demand and a linear-optics BSM in the quadrature basis can be performed without failure, entanglement can be swapped deterministically and verified without postselection [7,8]. However, due to the finite squeezing of both initial entanglement sources, the final entanglement after swapping in the ...

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Quantum Communication with Continuous Variables

Cited by 51 publications

References 175 publications

Realistic continuous-variable quantum teleportation with non-Gaussian resources

Realistic continuous-variable quantum teleportation with non-Gaussian resources

Enhanced multipartite quantum correlation by non-Gaussian operations

Entanglement Swapping between Discrete and Continuous Variables

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