Genuinely nonlocal sets without entanglement in multipartite systems

TL;DR

This paper constructs genuinely nonlocal sets of multipartite quantum states without entanglement, revealing new types of nonlocality in quantum systems and addressing open problems in the field.

Contribution

It introduces the first known genuinely nonlocal set of type I without entanglement in general multipartite systems and provides constructions for type II nonlocality.

Findings

Existence of genuinely nonlocal sets without entanglement in multipartite systems

Construction of type I genuinely nonlocal sets in general multipartite systems

Construction of type II genuinely nonlocal sets in specific tripartite and multipartite systems

Abstract

A set of multipartite orthogonal states is genuinely nonlocal if it is locally indistinguishable in every bipartition of the subsystems. If the set is locally reducible, we say it has genuine nonlocality of type \uppercase\expandafter{\romannumeral 1}. Otherwise, we say it has genuine nonlocality of type \uppercase\expandafter{\romannumeral 2}. Due to the complexity of the problem, the construction of genuinely nonlocal sets in general multipartite systems has not been completely solved so far. In this paper, we first provide a nonlocal set of product states in bipartite systems. We obtain a genuinely nonlocal set of type~\uppercase\expandafter{\romannumeral 1} without entanglement in general $n$-partite systems $\otimes^{n}_{i=1}\mathbb{C}^{d_{i}}$ $[3\leq (d_{1}-1)\leq d_{2}\leq \cdots\leq d_{n},n\geq3]$. Then we present two constructions with genuine nonlocality of type~\uppercase\expandafter{\romannumeral 2} in $\mathbb{C}^{d_{1}}\otimes\mathbb{C}^{d_{2}}\otimes\mathbb{C}^{d_{3}}$ $(3\leq d_{1}\leq d_{2}\leq d_{3})$ and $\otimes^{n}_{i=1}\mathbb{C}^{d_{i}}$ $(3\leq d_{1}\leq d_{2}\leq \cdots\leq d_{n},n\geq4)$. Our results further positively answer the open problem that there does exist a genuinely nonlocal set of type~\uppercase\expandafter{\romannumeral2} in multipartite systems [M. S. Li, Y. L. Wang, F. Shi, and M. H. Yung, J. Phys. A: Math. Theor. 54, 445301 (2021)] and highlight its related applications in quantum information processing.