Optimal estimation of an unknown maximally entangled state with local operations and classical communication
ShengLi Zhang, Xu‐Bo Zou, Ke Li, Chenhui Jin, Guang‐Can Guo · Physical Review A · 2007
We consider the optimal measurement procedures for estimating an unknown maximally entangled state with local operations and classical communications (LOCC). By the ``optimal,'' we mean that there is no other LOCC measurements that can provide a higher estimation fidelity. In fact, we first use the positive partial transpose constraint to obtain an upper bound of the fidelity; then, we show there exists a kind of LOCC measurement that can attain such a bound. The estimation fidelity of the optimal LOCC estimation procedures is $\frac{D+2}{(D+1){D}^{2}}$ with $D$ denoting the dimension of the relevant quantum system.