Pseudo standard entanglement structure cannot be distinguished from standard entanglement structure

TL;DR

This paper demonstrates that pseudo standard entanglement structures, which approximate standard entanglement, cannot be distinguished from true standard entanglement structures through experiments, highlighting the importance of global unitary symmetry.

Contribution

It introduces pseudo standard entanglement structures and shows they can approximate standard entanglement, revealing limitations of experimental verification in distinguishing them.

Findings

Infinitely many pseudo standard entanglement structures exist.

Pseudo structures can approximate maximally entangled states arbitrarily well.

Pseudo structures lack global unitary symmetry, unlike standard structures.

Abstract

An experimental verification of the maximally entangled state ensures that the constructed state is close to the maximally entangled state, but it does not guarantee that the state is exactly the same as the maximally entangled state. Further, the entanglement structure is not uniquely determined in general probabilistic theories even if we impose that the local subsystems are fully equal to quantum systems. Therefore, the existence of the maximally entangled state depends on whether the standard entanglement structure is valid. To examine this issue, we introduce pseudo standard entanglement structure as a structure of quantum composite system under natural assumptions based on the existence of projective measurements and the existence of approximations of all maximally entangled standard states. Surprisingly, there exist infinitely many pseudo standard entanglement structures different from the standard entanglement structure. In our setting, any maximally entangled state can be arbitrarily approximated by an entangled state that belongs to our obtained pseudo standard entanglement structure. That is, experimental verification does not exclude the possibility of our obtained pseudo standard entanglement structure that is different from the standard entanglement structure. On the other hand, such pseudo structures never possess global unitary symmetry, i.e., global unitary symmetry is essential condition for the standard entanglement structure.