Special core tensors of multi-qubit states and the concurrency of three lines

In this work, we propose a computationally simple approach to identify the local unitary (LU) entanglement classes of multi-qubit states by higher-order singular value decomposition (HOSVD). For multipartite states, HOSVD simultaneously diagonalizes their one-body reduced density matrices (RDM) by L...

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Bibliographic Details
Main Authors: Choong, Pak Shen, Zainuddin, Hishamuddin, Chan, Kar Tim, Said Husain, Sharifah Kartini
Format: Article
Published: Springer 2023
Online Access:http://psasir.upm.edu.my/id/eprint/109127/
https://link.springer.com/article/10.1007/s11128-023-03939-w?error=cookies_not_supported&code=474cfc27-c36f-4a6b-a9ae-030a092a1441
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Summary:In this work, we propose a computationally simple approach to identify the local unitary (LU) entanglement classes of multi-qubit states by higher-order singular value decomposition (HOSVD). For multipartite states, HOSVD simultaneously diagonalizes their one-body reduced density matrices (RDM) by LU actions. Therefore, the zeros of the all-orthogonality conditions due to HOSVD, also known as the core tensors, are the pure-state representations of such simultaneously diagonalized one-body RDM for a given multipartite state. By using the concurrency of three lines, we simplified the calculations and coarse-grained the classification into a finite number of families of states based on the square of their first n-mode singular values, σ1(n)2 . These special core tensors are genuinely entangled by default. For three and four qubits, we identified two and four families of states respectively. A generalization of the algorithm to multi-qubit states is provided.