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The problem of determining whether a given quantum state is entangled lies at the heart of quantum information processing, which is known to be an NP-hard problem in general. Despite the proposed many methods such as the positive partial…

Quantum Physics · Physics 2018-07-18 Sirui Lu , Shilin Huang , Keren Li , Jun Li , Jianxin Chen , Dawei Lu , Zhengfeng Ji , Yi Shen , Duanlu Zhou , Bei Zeng

Ever since entanglement was identified as a computational and cryptographic resource, researchers have sought efficient ways to tell whether a given density matrix represents an unentangled, or separable, state. This paper gives the first…

Quantum Physics · Physics 2007-05-23 Lawrence M. Ioannou

Ever since entanglement was identified as a computational and cryptographic resource, effort has been made to find an efficient way to tell whether a given density matrix represents an unentangled, or separable, state. Essentially, this is…

Data Structures and Algorithms · Computer Science 2007-05-23 Lawrence M. Ioannou

Determining whether a quantum state is separable or entangled is a problem of fundamental importance in quantum information science. It has recently been shown that this problem is NP-hard. There is a highly inefficient `basic algorithm'…

Quantum Physics · Physics 2009-11-10 L. M. Ioannou , B. C. Travaglione , D. Cheung , A. K. Ekert

Motivated by the Kronecker product approximation technique, we have developed a very simple method to assess the inseparability of bipartite quantum systems, which is based on a realigned matrix constructed from the density matrix. For any…

Quantum Physics · Physics 2007-05-23 Kai Chen , Ling-An Wu

The concept of entanglement and separability of quantum states is relevant for several fields in physics. Still, there is a lack of effective operational methods to characterise these features. We propose a method to certify quantum…

Quantum Physics · Physics 2024-03-06 Ties-A. Ohst , Xiao-Dong Yu , Otfried Gühne , H. Chau Nguyen

Separability is an important problem in theory of quantum entanglement. By using the Bloch representation of quantum states in terms of the Heisenberg-Weyl observable basis, we present a new separability criterion for bipartite quantum…

Quantum Physics · Physics 2020-02-04 Jingmei Chang , Meiyu Cui , Tinggui Zhang , Shao-Ming Fei

Entanglement is a fundamental aspect of quantum physics, both conceptually and for its many applications. Classifying an arbitrary multipartite state as entangled or separable -- a task referred to as the separability problem -- poses a…

For finite-dimensional bipartite quantum systems, we find the exact size of the largest balls, in spectral $l_p$ norms for $1 \le p \le \infty$, of separable (unentangled) matrices around the identity matrix. This implies a simple and…

Quantum Physics · Physics 2009-11-07 Leonid Gurvits , Howard Barnum

We provide a constructive algorithm to find the best separable approximation to an arbitrary density matrix of a composite quantum system of finite dimensions. The method leads to a condition of separability and to a measure of…

Quantum Physics · Physics 2009-10-30 Maciej Lewenstein , Anna Sanpera

The detection and estimation of quantum entanglement are the essential issues in the theory of quantum entanglement. We construct matrices based on the realignment of density matrices and the vectorization of the reduced density matrices,…

Quantum Physics · Physics 2024-05-21 Jiaxin Sun , Hongmei Yao , Shao-Ming Fei , Zhaobing Fan

Detection of entanglement through partial knowledge of the quantum state is a challenge to implement efficiently. Here we propose a separability criterion for detecting bipartite entanglement in arbitrary dimensional quantum states using…

Quantum Physics · Physics 2024-05-28 Shruti Aggarwal , Satyabrata Adhikari , A. S. Majumdar

The detection of entanglement in a bipartite state is a crucial issue in quantum information science. Based on realignment of density matrices and the vectorization of the reduced density matrices, we introduce a new set of separability…

Quantum Physics · Physics 2024-12-09 Yu Lu , Zhong-Xi Shen , Shao-Ming Fei , Zhi-Xi Wang

We study the separability of bipartite quantum systems in arbitrary dimensions using the Bloch representation of their density matrix. This approach enables us to find an alternative characterization of the separability problem, from which…

Quantum Physics · Physics 2024-12-05 Julio I. de Vicente

We present a quasipolynomial-time algorithm for solving the weak membership problem for the convex set of separable, i.e. non-entangled, bipartite density matrices. The algorithm decides whether a density matrix is separable or whether it…

Quantum Physics · Physics 2011-06-13 Fernando G. S. L. Brandao , Matthias Christandl , Jon Yard

We propose a unifying approach to the separability problem using covariance matrices of locally measurable observables. From a practical point of view, our approach leads to strong entanglement criteria that allow to detect the entanglement…

Quantum Physics · Physics 2007-10-04 O. Gühne , P. Hyllus , O. Gittsovich , J. Eisert

We consider entanglement detection for quantum key distribution systems that use two signal states and continuous variable measurements. This problem can be formulated as a separability problem in a qubit-mode system. To verify…

Quantum Physics · Physics 2007-05-23 Johannes Rigas , Otfried Gühne , Norbert Lütkenhaus

We focus on determining the separability of an unknown bipartite quantum state $\rho$ by invoking a sufficiently large subset of all possible entanglement witnesses given the expected value of each element of a set of mutually orthogonal…

Quantum Physics · Physics 2009-11-13 Lawrence M. Ioannou , Benjamin C. Travaglione

The detection of multipartite entanglement in arbitrary dimensional systems is investigated. We derive useful $k$-separability criteria of mixed $n$-partite ($n\geq 3$) quantum states to detect $k$-nonseparable $n$-partite quantum states.…

Quantum Physics · Physics 2013-01-17 Ting Gao , Yan Hong

Entanglement is a fundamental feature of quantum mechanics, playing a crucial role in quantum information processing. However, classifying entangled states, particularly in the mixed-state regime, remains a challenging problem, especially…

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