Beating the code breakers

Ekert, Artur

doi:10.1038/358014a0

Cited by 50 publications

(21 citation statements)

References 5 publications

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“…In this respect quantum entanglement represents the basis of the exponential parallelism of future quantum computers [1], of quantum teleportation [2][3][4][5] and of some kinds of cryptographic communications [6,7]. In practical realizations, however, entanglement is degraded by decoherence and dissipation processes that result from unavoidable couplings with the environment.…”

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confidence: 99%

Detection of Entanglement with Polarized Photons: Experimental Realization of an Entanglement Witness

et al. 2003

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We report on the first experimental realization of the entanglement witness for polarization entangled photons. It represents a recently discovered significant quantum information protocol which is based on few local measurements.The present demonstration has been applied to the so-called Werner states, a family of "mixed" quantum states that include both entangled and non entangled states. These states have been generated by a novel high brilliance source of entanglement which allows to continuously tune the degree of mixedness.Typeset using REVT E X 1

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confidence: 99%

Detection of Entanglement with Polarized Photons: Experimental Realization of an Entanglement Witness

et al. 2003

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“…It appears to be the basis for a proper understanding of the emerging fields of quantum computation [2], quantum communication [3], and quantum cryptography [4]. Although some fundamental results have been obtained recently such as the quantum noiseless coding theorem [5] or the rules governing the extraction of classical information from quantum entropy, it is still puzzling in many respects.…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Negative Entropy in Quantum Information Theory

Cerf

Adami

1997

New Developments on Fundamental Problems in Quantum Physics

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We present a quantum information theory that allows for the consistent description of quantum entanglement. It parallels classical (Shannon) information theory but is based entirely on density matrices, rather than probability distributions, for the description of quantum ensembles. We find that, unlike in Shannon theory, conditional entropies can be negative when considering quantum entangled systems such as an Einstein-Podolsky-Rosen pair, which leads to a violation of well-known bounds of classical information theory. Negative quantum entropy can be traced back to "conditional" density matrices which admit eigenvalues larger than unity. A straightforward definition of mutual quantum entropy, or "mutual entanglement", can also be constructed using a "mutual" density matrix. Such a unified information-theoretic description of classical correlation and quantum entanglement clarifies the link between them: the latter can be viewed as "super-correlation" which can induce classical correlation when considering a ternary or larger system. INTRODUCTIONQuantum information theory [1] is a new field with potential implications for the conceptual foundations of quantum mechanics. It appears to be the basis for a proper understanding of the emerging fields of quantum computation [2], quantum communication [3], and quantum cryptography [4]. Although some fundamental results have been *

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“…Quantum copying has applications in quantum cryptography and signal transmission-a field in which presently theoretical and first experimental results are available [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. It can also find uses in quantum computing, reviewed, e.g., in [24][25][26][27][28][29][30][31][32][33].…”

Section: Introduction and Definition Of The Modelmentioning

confidence: 99%

Quantum Signal Splitting that Avoids Initialization of the Targets

Privman

1997

Mod. Phys. Lett. B

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The classical signal splitting and copying are not possible in quantum mechanics. Specifically, one cannot copy the basis up and down states of the input (I) two-state system (qubit, spin) into the copy (C) and duplicate-copy (D) two-state systems if the latter systems are initially in an arbitrary state. We consider instead a quantum evolution in which the basis states of I at time t are duplicated in at least two of the systems I, C, D, at time t + ∆t. In essence, the restriction on the initial target states is exchanged for uncertainty as to which two of the three qubits retain copies of the initial source state.

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Beating the code breakers

Cited by 50 publications

References 5 publications

Detection of Entanglement with Polarized Photons: Experimental Realization of an Entanglement Witness

Detection of Entanglement with Polarized Photons: Experimental Realization of an Entanglement Witness

Negative Entropy in Quantum Information Theory

Quantum Signal Splitting that Avoids Initialization of the Targets

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