Two-way classical communication remarkably improves local distinguishability

Understand

We analyze the difference in the local distinguishability among the following three restrictions; (i) Local operations and only one-way classical communications (one-way LOCC) are permitted.

• (ii) Local operations and two-way classical communications (two-way LOCC) are permitted.
• (iii) All separable operations are permitted.
• We obtain two main results concerning the discrimination between a given bipartite pure state and the completely mixed state with the condition that the given state should be detected perfectly.