Identifying families of multipartite states with non-trivial local entanglement transformations

TL;DR

This paper investigates the structure of multipartite entangled states under local operations and classical communication, identifying classes that are fully convertible and those that exhibit weak isolation, with a focus on antisymmetric states.

Contribution

It demonstrates that the SLOCC class of the 3-qutrit antisymmetric state is free of isolation and explores the LOCC convertibility properties of various entangled state classes.

Findings

The 3-qutrit antisymmetric state class is isolation-free and fully convertible with one-round LOCC.

Most other classes, including n-qunit antisymmetric states for n≥4, exhibit weak isolation.

The structure and entanglement properties of the 3-qutrit antisymmetric class are analyzed in detail.

Abstract

The study of state transformations by spatially separated parties with local operations assisted by classical communication (LOCC) plays a crucial role in entanglement theory and its applications in quantum information processing. Transformations of this type among pure bipartite states were characterized long ago and have a revealing theoretical structure. However, it turns out that generic fully entangled pure multipartite states cannot be obtained from nor transformed to any inequivalent fully entangled state under LOCC. States with this property are referred to as isolated. Nevertheless, the above result does not forbid the existence of particular SLOCC classes that are free of isolation, and therefore, display a rich structure regarding LOCC convertibility. In fact, it is known that the celebrated $n$-qubit GHZ and W states give particular examples of such classes and in this work, we investigate this question in general. One of our main results is to show that the SLOCC class of the 3-qutrit totally antisymmetric state is isolation-free as well. Actually, all states in this class can be converted to inequivalent states by LOCC protocols with just one round of classical communication (as in the GHZ and W cases). Thus, we consider next whether there are other classes with this property and we find a large set of negative answers. Indeed, we prove weak isolation (i.e., states that cannot be obtained with finite-round LOCC nor transformed by one-round LOCC) for very general classes, including all SLOCC families with compact stabilizers and many with non-compact stabilizers, such as the classes corresponding to the $n$-qunit totally antisymmetric states for $n\geq4$. Finally, given the pleasant feature found in the family corresponding to the 3-qutrit totally antisymmetric state, we explore in more detail the structure induced by LOCC and the entanglement properties within this class.