Peres–Horodecki criterion
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Peres–Horodecki criterion
Peres–Horodecki criterion
The Peres–Horodecki criterion is a necessary condition, for the jointdensity matrixof two quantum mechanical systemsand, to beseparable. It is also called the PPT criterion, for positive partial transpose. In the 2x2 and 2x3 dimensional cases the condition is also sufficient. It is used to decide the separability ofmixed states, where theSchmidt decompositiondoes not apply.
In higher dimensions, the test is inconclusive, and one should supplement it with more advanced tests, such as those based on entanglement witnesses.
Definition
If we have a general statewhich acts on
Its partial transpose (with respect to the B party) is defined as
Note that the partial in the name implies that only part of the state is transposed. More precisely,is the identitymapapplied to the A party and the transposition map applied to the B party.
This definition can be seen more clearly if we write the state as a block matrix:
Where, and each block is a square matrix of dimension. Then the partial transpose is
The criterion states that ifis separable,has non-negativeeigenvalues. In other words, ifhas a negative eigenvalue,is guaranteed to beentangled. If the eigenvalues are non-negative, and the dimension is larger than 6, the test is inconclusive.
The result is independent of the party that was transposed, because.
Example
Consider this 2-qubit family of Werner states:
It can be regarded as theconvex combinationof, amaximally entangled state, and identity, the maximally mixed state.
Its density matrix is
and the partial transpose
Its least eigenvalue is. Therefore, the state is entangled for.
Demonstration
If ρ is separable, it can be written as
In this case, the effect of the partial transposition is trivial:
As the transposition map preserves eigenvalues, the spectrum ofis the same as the spectrum of, and in particularmust still be positive semidefinite. Thusmust also be positive semidefinite. This proves the necessity of the PPT criterion.
Showing that being PPT is also sufficient for the 2 X 2 and 3 X 2 (equivalently 2 X 3) cases is more involved. It was shown by the Horodeckis that for every entangled state there exists an entanglement witness. This is a result of geometric nature and invokes the Hahn–Banach theorem (see reference below).
From the existence of entanglement witnesses, one can show thatbeing positive for allpositive mapsΛ is a necessary and sufficient condition for the separability of ρ, where Λ mapsto
Furthermore, every positive map fromtocan be decomposed into a sum of completely positive and completely copositive maps, whenand. In other words, every such map Λ can be written as
whereandare completely positive and T is the transposition map. This follows from the Størmer-Woronowicz theorem.
Loosely speaking, the transposition map is therefore the only one that can generate negative eigenvalues in these dimensions. So ifis positive,is positive for any Λ. Thus we conclude that the Peres–Horodecki criterion is also sufficient for separability when.
In higher dimensions, however, there exist maps that can't be decomposed in this fashion, and the criterion is no longer sufficient. Consequently, there are entangled states which have a positive partial transpose. Such states have the interesting property that they are bound entangled, i.e. they can not be distilled for quantum communication purposes.
Continuous variable systems
The Peres–Horodecki criterion has been extended to continuous variable systems. Simon [1] formulated a particular version of the PPT criterion in terms of the second-order moments of canonical operators and showed that it is necessary and sufficient for-mode Gaussian states (see Ref.[2] for a seemingly different but essentially equivalent approach). It was later found [3] that Simon's condition is also necessary and sufficient for-mode Gaussian states, but no longer sufficient for-mode Gaussian states. Simon's condition can be generalized by taking into account the higher order moments of canonical operators [4][5] or by using entropic measures.[6][7]
References
[1]
Citation Link//www.ncbi.nlm.nih.gov/pubmed/11017310Simon, R. "Peres-Horodecki Separability Criterion for Continuous Variable Systems". Physical Review Letters. 84 (12): 2726–2729. arXiv:quant-ph/9909044. Bibcode:2000PhRvL..84.2726S. doi:10.1103/PhysRevLett.84.2726. PMID 11017310.
Sep 26, 2019, 11:00 PM
[2]
Citation Link//doi.org/10.1103%2FPhysRevLett.84.2722Duan, Lu-Ming; Giedke, G.; Cirac, J. I.; Zoller, P. "Inseparability Criterion for Continuous Variable Systems". Physical Review Letters. 84 (12): 2722–2725. arXiv:quant-ph/9908056. Bibcode:2000PhRvL..84.2722D. doi:10.1103/PhysRevLett.84.2722.
Sep 26, 2019, 11:00 PM
[3]
Citation Link//doi.org/10.1103%2FPhysRevLett.86.3658Werner, R. F.; Wolf, M. M. "Bound Entangled Gaussian States". Physical Review Letters. 86 (16): 3658–3661. arXiv:quant-ph/0009118. Bibcode:2001PhRvL..86.3658W. doi:10.1103/PhysRevLett.86.3658.
Sep 26, 2019, 11:00 PM
[4]
Citation Link//doi.org/10.1103%2FPhysRevLett.95.230502Shchukin, E.; Vogel, W. "Inseparability Criteria for Continuous Bipartite Quantum States". Physical Review Letters. 95 (23). arXiv:quant-ph/0508132. Bibcode:2005PhRvL..95w0502S. doi:10.1103/PhysRevLett.95.230502.
Sep 26, 2019, 11:00 PM
[5]
Citation Link//www.ncbi.nlm.nih.gov/pubmed/16486912Hillery, Mark; Zubairy, M. Suhail. "Entanglement Conditions for Two-Mode States". Physical Review Letters. 96 (5): 050503. arXiv:quant-ph/0507168. Bibcode:2006PhRvL..96e0503H. doi:10.1103/PhysRevLett.96.050503. PMID 16486912.
Sep 26, 2019, 11:00 PM
[6]
Citation Link//www.ncbi.nlm.nih.gov/pubmed/19905682Walborn, S.; Taketani, B.; Salles, A.; Toscano, F.; de Matos Filho, R. "Entropic Entanglement Criteria for Continuous Variables". Physical Review Letters. 103 (16): 160505. arXiv:0909.0147. Bibcode:2009PhRvL.103p0505W. doi:10.1103/PhysRevLett.103.160505. PMID 19905682.
Sep 26, 2019, 11:00 PM
[7]
Citation Link//doi.org/10.1109%2FTIT.2013.2257936Yichen Huang (October 2013). "Entanglement Detection: Complexity and Shannon Entropic Criteria". IEEE Transactions on Information Theory. 59 (10): 6774–6778. doi:10.1109/TIT.2013.2257936.
Sep 26, 2019, 11:00 PM
[11]
Citation Link//doi.org/10.1016%2Fs0375-9601%2896%2900706-210.1016/s0375-9601(96)00706-2
Sep 26, 2019, 11:00 PM
[14]
Citation Link//doi.org/10.1016%2F0034-4877%2876%2990038-010.1016/0034-4877(76)90038-0
Sep 26, 2019, 11:00 PM