scholarly journals Characterization and properties of weakly optimal entanglement witnesses

2015 ◽  
Vol 15 (13&14) ◽  
pp. 1109-1121
Author(s):  
Bang-Hai Wang ◽  
Hai-Ru Xu ◽  
Steve Campbell ◽  
Simone Severini
Keyword(s):  
Hilbert Space ◽  
Identity Matrix ◽  
Negative Number ◽  
Entanglement Witness ◽  
Geometric Properties ◽  
Expectation Value ◽  
Separable States ◽  
Entanglement Witnesses ◽  
Product Vector

We present an analysis of the properties and characteristics of weakly optimal entanglement witnesses, that is witnesses whose expectation value vanishes on at least one product vector. Any weakly optimal entanglement witness can be written as the form of $W^{wopt}=\sigma-c_{\sigma}^{max} I$, where $c_{\sigma}^{max}$ is a non-negative number and $I$ is the identity matrix. We show the relation between the weakly optimal witness $W^{wopt}$ and the eigenvalues of the separable states $\sigma$. Further we give an application of weakly optimal witnesses for constructing entanglement witnesses in a larger Hilbert space by extending the result of [P. Badzi\c{a}g {\it et al}, Phys. Rev. A {\bf 88}, 010301(R) (2013)], and we examine their geometric properties.

Some Remarks on the Role of Minimal Length of Positive Maps in Constructing Entanglement Witnesses

2004 ◽  
Vol 11 (04) ◽  
pp. 385-390 ◽  
Author(s):  
A. Jamiołkowski
Keyword(s):  
Hilbert Space ◽  
Minimal Length ◽  
Completely Positive ◽  
Positive Map ◽  
Separable States ◽  
Positive Maps ◽  
Entanglement Witnesses ◽  
Adjoint Operators

The main objective of this paper is to discuss correspondence between the concept of entanglement witnesses (self-adjoint operators on a composite Hilbert space [Formula: see text] that are, in general, not positive, but are positive on separable states) and positive maps [Formula: see text] which are not completely positive. The notion of minimal length of linear positive map is introduced and the role of this quantity in the constructing of entanglement witnesses is explained.

scholarly journals DUALITIES AND POSITIVITY IN THE STUDY OF QUANTUM ENTANGLEMENT

2010 ◽  
Vol 08 (05) ◽  
pp. 721-754 ◽  
Author(s):  
ŁUKASZ SKOWRONEK
Keyword(s):  
Related Problem ◽  
Separable State ◽  
Real Numbers ◽  
Entanglement Witness ◽  
Separable States ◽  
Entanglement Witnesses ◽  
Real Polynomials ◽  
Schmidt Rank ◽  
Families Of Operators ◽  
Cone Duality

We present a survey on mathematical topics relating to separable states and entanglement witnesses. The convex cone duality between separable states and entanglement witnesses is discussed and later generalized to other families of operators, leading to their characterization via multiplicative properties. The condition for an operator to be an entanglement witness is rephrased as a problem of positivity of a family of real polynomials. By solving the latter in a specific case of a three-parameter family of operators, we obtain explicit description of entanglement witnesses belonging to that family. A related problem of block positivity over real numbers is discussed. We also consider a broad family of block positivity tests and prove that they can never be sufficient, which should be useful in case of future efforts in that direction. Finally, we introduce the concept of length of a separable state and present new results concerning relationships between the length and Schmidt rank. In particular, we prove that separable states of length lower or equal to 3 have Schmidt ranks equal to their lengths. We also give an example of a state which has length 4 and Schmidt rank 3.

scholarly journals Distance between Bound Entangled States from Unextendible Product Bases and Separable States

2020 ◽  
Vol 2 (1) ◽  
pp. 49-56 ◽  
Author(s):  
Marcin Wieśniak ◽  
Palash Pandya ◽  
Omer Sakarya ◽  
Bianka Woloncewicz
Keyword(s):  
The State ◽  
Reference State ◽  
Entangled States ◽  
Separable State ◽  
Entanglement Witness ◽  
Separable States ◽  
Entanglement Witnesses

We discuss the use of the Gilbert algorithm to tailor entanglement witnesses for unextendible product basis bound entangled states (UPB BE states). The method relies on the fact that an optimal entanglement witness is given by a plane perpendicular to a line between the reference state, entanglement of which is to be witnessed, and its closest separable state (CSS). The Gilbert algorithm finds an approximation of CSS. In this article, we investigate if this approximation can be good enough to yield a valid entanglement witness. We compare witnesses found with Gilbert algorithm and those given by Bandyopadhyay–Ghosh–Roychowdhury (BGR) construction. This comparison allows us to learn about the amount of entanglement and we find a relationship between it and a feature of the construction of UPBBE states, namely the size of their central tile. We show that in most studied cases, witnesses found with the Gilbert algorithm in this work are more optimal than ones obtained by Bandyopadhyay, Ghosh, and Roychowdhury. This result implies the increased tolerance to experimental imperfections in a realization of the state.

Simplifying Schmidt number witnesses via higher-dimensional embeddings

2004 ◽  
Vol 4 (3) ◽  
pp. 207-221
Author(s):  
F. Hulpke ◽  
D. Bruss ◽  
M. Levenstein ◽  
A. Sanpera
Keyword(s):  
Hilbert Space ◽  
Schmidt Number ◽  
Convex Sets ◽  
Entanglement Witness ◽  
Simple Method ◽  
Dimensional Hilbert Space ◽  
Higher Dimensional ◽  
Arbitrary Convex

We apply the generalised concept of witness operators to arbitrary convex sets, and review the criteria for the optimisation of these general witnesses. We then define an embedding of state vectors and operators into a higher-dimensional Hilbert space. This embedding leads to a connection between any Schmidt number witness in the original Hilbert space and a witness for Schmidt number two (i.e. the most general entanglement witness) in the appropriate enlarged Hilbert space. Using this relation we arrive at a conceptually simple method for the construction of Schmidt number witnesses in bipartite systems.

scholarly journals An elementary introduction to the geometry of quantum states with pictures

2019 ◽  
Vol 32 (02) ◽  
pp. 2030001 ◽  
Author(s):  
J. Avron ◽  
O. Kenneth
Keyword(s):  
Convex Body ◽  
Cross Sections ◽  
Convex Bodies ◽  
Quantum States ◽  
Entangled States ◽  
High Dimensions ◽  
Geometric Properties ◽  
Precise Sense ◽  
Entanglement Witnesses ◽  
Elementary Methods

This is a review of the geometry of quantum states using elementary methods and pictures. Quantum states are represented by a convex body, often in high dimensions. In the case of [Formula: see text] qubits, the dimension is exponentially large in [Formula: see text]. The space of states can be visualized, to some extent, by its simple cross sections: Regular simplexes, balls and hyper-octahedra. a When the dimension gets large, there is a precise sense in which the space of states resembles, almost in every direction, a ball. The ball turns out to be a ball of rather low purity states. We also address some of the corresponding, but harder, geometric properties of separable and entangled states and entanglement witnesses. “All convex bodies behave a bit like Euclidean balls.” Keith Ball

scholarly journals CLASSICAL TENSORS AND QUANTUM ENTANGLEMENT I: PURE STATES

2010 ◽  
Vol 07 (03) ◽  
pp. 485-503 ◽  
Author(s):  
P. ANIELLO ◽  
J. CLEMENTE-GALLARDO ◽  
G. MARMO ◽  
G. F. VOLKERT
Keyword(s):  
Hilbert Space ◽  
Symplectic Geometry ◽  
Vector Fields ◽  
Riemannian Metric ◽  
Inner Product ◽  
Tensor Fields ◽  
Metric Tensor ◽  
Separable States ◽  
Pure States ◽  
Complex Projective

The geometrical description of a Hilbert space associated with a quantum system considers a Hermitian tensor to describe the scalar inner product of vectors which are now described by vector fields. The real part of this tensor represents a flat Riemannian metric tensor while the imaginary part represents a symplectic two-form. The immersion of classical manifolds in the complex projective space associated with the Hilbert space allows to pull-back tensor fields related to previous ones, via the immersion map. This makes available, on these selected manifolds of states, methods of usual Riemannian and symplectic geometry. Here, we consider these pulled-back tensor fields when the immersed submanifold contains separable states or entangled states. Geometrical tensors are shown to encode some properties of these states. These results are not unrelated with criteria already available in the literature. We explicitly deal with some of these relations.

Geometric properties for a family of holomorphic functions associated with Wanas operator defined on complex Hilbert space

2020 ◽  
pp. 2150122
Author(s):  
Abbas Karem Wanas ◽  
Junesang Choi ◽  
Nak Eun Cho
Keyword(s):  
Hilbert Space ◽  
Extreme Points ◽  
Holomorphic Functions ◽  
Complex Hilbert Space ◽  
Coefficient Estimates ◽  
Geometric Properties

By making use of Wanas operator, we aim to introduce and investigate a certain family of univalent holomorphic functions with negative coefficients defined on complex Hilbert space. We present some important geometric properties of this family such as coefficient estimates, convexity, distortion and growth, radii of starlikeness and convexity. We also discuss the extreme points for functions belonging to this family.

scholarly journals A Quantum Expectation Value Based Language Model with Application to Question Answering

Entropy ◽  
2020 ◽  
Vol 22 (5) ◽  
pp. 533
Author(s):  
Qin Zhao ◽  
Chenguang Hou ◽  
Changjian Liu ◽  
Peng Zhang ◽  
Ruifeng Xu
Keyword(s):  
Hilbert Space ◽  
Density Matrix ◽  
Question Answering ◽  
Language Model ◽  
Language Models ◽  
Quantum Model ◽  
Expectation Value ◽  
Proposed Model ◽  
Matching Score ◽  
The Relationship

Quantum-inspired language models have been introduced to Information Retrieval due to their transparency and interpretability. While exciting progresses have been made, current studies mainly investigate the relationship between density matrices of difference sentence subspaces of a semantic Hilbert space. The Hilbert space as a whole which has a unique density matrix is lack of exploration. In this paper, we propose a novel Quantum Expectation Value based Language Model (QEV-LM). A unique shared density matrix is constructed for the Semantic Hilbert Space. Words and sentences are viewed as different observables in this quantum model. Under this background, a matching score describing the similarity between a question-answer pair is naturally explained as the quantum expectation value of a joint question-answer observable. In addition to the theoretical soundness, experiment results on the TREC-QA and WIKIQA datasets demonstrate the computational efficiency of our proposed model with excellent performance and low time consumption.

scholarly journals QUANTUM BACKREACTION (CASIMIR) EFFECT WITHOUT INFINITIES: ALGEBRAIC ANALYSIS

2012 ◽  
Vol 14 ◽  
pp. 376-382
Author(s):  
ANDRZEJ HERDEGEN
Keyword(s):  
Hilbert Space ◽  
Quantum Theory ◽  
Quantum System ◽  
Casimir Effect ◽  
Quantum Field ◽  
Expectation Value ◽  
Physical Systems ◽  
Algebra Of Observables ◽  
General Terms ◽  
External Conditions

Casimir effect, in most general terms, is the backreaction of a quantum system responding to an adiabatic change of external conditions. This backreaction is expected to be quantitatively measured by a change in the expectation value of a certain energy observable of the system. However, for this concept to be applicable, the system has to retain its identity in the process. Most prevailing tendencies in the analysis of the effect seem to ignore this question. In general, a quantum theory is defined by an algebra of observables, whose representations by operators in a Hilbert space define concrete physical systems described by the theory. A quantum system retains its identity if both the algebra as well as its representation do not change. We discuss the resulting restrictions for admissible models of changing external conditions. These ideas are applied to quantum field models. No infinities arise, if the algebraic demands are respected.

scholarly journals Completing bases in four dimensions

2022 ◽  
Author(s):  
Hans Havlicek ◽  
Karl Svozil
Keyword(s):  
Hilbert Space ◽  
Quantum States ◽  
Four Dimensions ◽  
Separable States ◽  
Orthogonal Representation ◽  
Relational Properties ◽  
Dimensional Hilbert Space ◽  
Physical Entanglement

Abstract Criteria for the completion of an incomplete basis of, or context in, a four-dimensional Hilbert space by (in)decomposable vectors are given. This, in particular, has consequences for the task of ``completing'' one or more bases or contexts of a (hyper)graph: find a complete faithful orthogonal representation (aka coordinatization) of a hypergraph when only a coordinatization of the intertwining observables is known. In general indecomposability and thus physical entanglement and the encoding of relational properties by quantum states ``prevails'' and occurs more often than separability associated with well defined individual, separable states.

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