Cited by 8,290Quantum Information and CryptographyQuantum Mechanics and ApplicationsQuantum many-body systems

Entanglement of Formation of an Arbitrary State of Two Qubits

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Wootters, William K.·1998·Physical Review Letters

Abstract

The entanglement of a pure state of a pair of quantum systems is defined as the entropy of either member of the pair. The entanglement of formation of a mixed state $\ensuremath{\rho}$ is the minimum average entanglement of an ensemble of pure states that represents \ensuremath{\rho}. An earlier paper conjectured an explicit formula for the entanglement of formation of a pair of binary quantum objects (qubits) as a function of their density matrix, and proved the formula for special states. The present paper extends the proof to arbitrary states of this system and shows how to construct entanglement-minimizing decompositions.

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  • Concurrence, entanglement of formation, and tangle are measures of the quantum-coherence properties of a mixed quantum state.

    “The concurrence, entanglement of formation and tangle are measures of the quantum-coherence properties of a mixed quantum state [29].”

    From Measurement of qubits (2001) · cites this paper as [29]

    The Abstract (pp. 1, 4) defines entanglement of formation for mixed states of two qubits and says concurrence can serve as a measure of entanglement. The paper does not address tangle as a measure, and it describes these quantities as measures of entanglement rather than of quantum-coherence properties generally. (LLM, conf=0.88)

    Experimental — accuracy not yet measured
  • Wootters' original definition of concurrence is invalid for two-qudit states with d > 2.

    “As for the concurrence, rigorously, its original Wootters' definition [20] is invalid for two-qudit states with d > 2.”

    From Entanglement of biphoton states: qutrits and ququarts (2011) · cites this paper as [20]

    The discussion on pp. 2–4 defines concurrence and proves its use for two-qubit states. It does not address two-qudit states with d > 2 or establish that the definition is invalid for them. (LLM, conf=0.82)

    Experimental — accuracy not yet measured
  • For bipartite states with one-particle Hilbert space dimension d=2, there is a simple algebraic relation between Wootters' concurrence C and the Schmidt entanglement parameter K, giving equation (5.3).

    “It is also known [19] that in the case of bipartite states with the dimensionality of the oneparticle Hilbert space d = 2, there is a simple algebraic relation between Wootters' concurrence C [20] and the Schmidt entanglement parameter K , owing to which”

    From Entanglement of biphoton states: qutrits and ququarts (2011) · cites this paper as [20]

  • Expressions for concurrence C (5.3 and last formula of 5.4) can also be derived directly from Wootters' original definition [20].

    “Note that expressions for the concurrence C (equation (5.3) and the last formula of equation (5.4)) can also be derived directly from the original Wootters' definition [20].”

    From Entanglement of biphoton states: qutrits and ququarts (2011) · cites this paper as [20]

  • The entanglement shared through the channel can be distilled into pure singlets and used for teleportation.

    “This entanglement, being that of a 2 × 2 system, can also be distilled [7] into pure singlets and used for teleportation.”

    From Quantum Communication through an Unmodulated Spin Chain (2003) · cites this paper as [7]

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Authors
Wootters, W. K.
Affiliations
Williams College (US)
Corresponding author
Wootters, William K.
Venue
Physical Review Letters
Published
1998-03-09
Volume
80
Issue
10
Pages
2245-2248
ISSN
  • 0031-9007 (ISSN-L)
  • 1079-7114
OpenAlex
W2011208902
Cited by
8,290
References
21
Citations by year
2026: 320 · 2025: 387 · 2024: 339 · 2023: 340 · 2022: 349 · 2021: 371 · 2020: 328 · 2019: 336 · 2018: 325 · 2017: 301 · 2016: 406 · 2015: 339 · 2014: 381 · 2013: 368 · 2012: 381
FWCI
62.08
Type
journal article
Language
en
Open access
Locations
  • Physical Review Letters (publishedVersion)
  • arXiv (Cornell University) (submittedVersion)
  • CERN Document Server (European Organization for Nuclear Research) (submittedVersion)
  • arXiv (Cornell University)
Topics
  • Physical Sciences › Computer Science › Artificial Intelligence › Quantum Information and Cryptography
  • Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Quantum Mechanics and Applications
  • Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Quantum many-body systems
Keywords
entanglement of formation, two-qubit states, mixed states, density matrix, quantum entanglement

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