Bargmann invariants and local unitary equivalence

In this paper, we study the local unitary equivalence of quantum states on $\mathbb{C}^n\otimes\mathbb{C}^n$, which is an important notion in quantum information theory.

For the case $n=2$, the local unitary orbits of two-qubit states are completely determined by their local unitary Bargmann invariants.

We show that the local unitary Bargmann invariants do not form a complete set of invariants of local unitary orbits for $n\geqslant 3$, which negatively answers a problem proposed by L.

Zhang and B.

Xie.