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arXiv:2411.07065 · Scientific Reports

Entanglement witnesses and separability criteria based on generalized equiangular tight frames

Katarzyna Siudzińska

Published Aug 14, 2025• 8 citations
arXivHTMLPDF

Abstract

In quantum information theory, measurements are represented by positive, operator-valued measures. In this paper, we use the operators corresponding to generalized equiangular measurements to construct positive maps. Their positivity follows from the properties of index of coincidence for few equiangular tight frames. These maps give rise to entanglement witnesses, which include as special cases many important classes considered in the literature. Additionally, we introduce separability criteria based on the correlation matrix and analyze them for various types of measurements.

DOI
10.1038/s41598-025-13403-7

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In quantum information theory, measurements are represented by positive, operator-valued measures. In this paper, we use the operators corresponding to generalized equiangular measurements to construct positive maps. Their positivity follows from the properties of index of coincidence for few equiangular tight frames. These maps give rise to entanglement witnesses, which include as special cases many important classes considered in the literature. Additionally, we introduce separability criteria based on the correlation matrix and analyze them for various types of measurements.
Abstract Finite tight frames play an important role in miscellaneous areas, including quantum information theory. Here we apply a class of tight frames, equiangular tight frames, to address the problem of detecting the entanglement of bipartite states. Here we derive some entanglement criteria based on positive operator-valued measurements built from equiangular tight frames. We also present a class of entanglement witnesses based on the equiangular tight frames. At last, we generalize the entanglement criterion for bipartite systems to multipartite systems.
Abstract Methods of quantum information processing often appear in terms of specially selected states. For example, mutually unbiased bases (MUBs) and symmetric informationally complete measurements are widely applied. Finite frames have found use in many areas including quantum information. Due to its specific inner structure, a single equiangular tight frame (ETF) allows one to formulate criteria to detect non-classical correlations. This study aims to approach entanglement detection with the use of mutually unbiased ETFs. Such frames are an interesting generalization of widely recognized MUBs. It still uses rank-one operators, but the number of outcomes can exceed the dimensionality. Several approaches are considered including separability criteria and entanglement witnesses. Separability criteria for multipartite systems are finally obtained.
Abstract The detection of quantum entanglement is an essential issue in the theory of quantum information. Recently, an elegant separability criterion to detect the entanglement of arbitrary-dimensional bipartite states is presented in Shi (2024 J. Phys. A: Math. Theor. 57 075302) by applying the positive operator valued measurements based on the equiangular tight frames (ETFs). Here we derive two enhanced separability criteria for detecting bipartite entanglement in arbitrary-dimensional quantum states using ETFs. Furthermore, we prove that they are not weaker than the criterion proposed in Shi (2024 J. Phys. A: Math. Theor. 57 075302).
Abstract Improvement of the detection ability of quantum entanglement is one of the essential tasks in quantum computing and quantum information. Finite tight frames play a fundamental role in a wide variety of areas and, generally, each application requires a specific class of frames and is closely related to quantum measurement. It is worth noting that a maximal set of complex equiangular vectors is closely related to a symmetric informationally complete measurement. Hence, our goal in this work is to propose a series of separability criteria assigned to a finite tight frame and some well-known inequalities in different quantum systems, respectively. In addition, some tighter criteria to detect entanglement for many-body quantum states are presented in arbitrary dimensions. Finally, the effectiveness of the proposed entanglement detection criteria is illustrated through some detailed examples.
Families of kkk-positive maps and Schmidt number witnesses from generalized equiangular measurements
Quantum entanglement is an important resource in many modern technologies, like quantum computation or quantum communication and information processing. Therefore, most interest is given to detect and quantify entangled states. Entanglement degree of bipartite mixed quantum states can be measured using the Schmidt number. Witnesses of the Schmidt number are closely related to kkk-positive linear maps, for which there is no general construction. Here, we use the generalized equiangular measurements to define a family of kkk-positive linear maps and the corresponding Schmidt number witnesses. We present examples of witnesses that detect two-parameter entangled states with Schmidt number k+1k+1k+1 in any dimension. Our approach allows for a more efficient entanglement quantification than other known Schmidt number witnesses constructed from symmetric measurement operators.
Finite tight frames are interesting in various topics including questions of quantum information. Each complex tight frame leads to a resolution of the identity in the Hilbert space. Symmetric informationally complete measurements are a special class of equiangular tight frames. Applications of such frames in quantum physics deserve more attention than they have obtained. We derive uncertainty relations for a quantum measurement assigned to an equiangular tight frame. Main results follow from estimation of the corresponding index of coincidence. State-dependent and state-independent formulations are both addressed. Also, we discuss applications of considered measurements to detect entanglement and other correlations.