Center for Quantum Information and Quantum Control (CQIQC), Department of Physics, University of Toronto, Toronto, Ontario, M5S 3G4, Canada.
Phys Rev Lett. 2012 Jun 15;108(24):240504. doi: 10.1103/PhysRevLett.108.240504.
Quantum entanglement is fundamentally related to the operational setting of local quantum operations and classical communication (LOCC). A more general class of operations known as separable operations (SEP) is often employed to approximate LOCC, but the exact difference between LOCC and SEP is unknown. In this letter, we compare the two classes in performing particular tripartite to bipartite entanglement conversions and report a gap as large as 12.5% between SEP and LOCC, which is the first known appreciable gap between the classes. Our results rely on constructing a computable entanglement monotone with a clear operational meaning that, unlike all other such monotones previously studied, is not monotonic under SEP. Finally, we prove the curious fact that convergent sequences of LOCC protocols need not be LOCC feasible in the limit.
量子纠缠与局域量子操作和经典通信（LOCC）的操作设置有着根本的联系。一种通常被用来近似 LOCC 的更一般的操作类被称为可分离操作（SEP），但 LOCC 和 SEP 之间的确切区别尚不清楚。在这封信中，我们比较了这两种方法在执行特定的三分量到两分量纠缠转换方面的效果，并报告了 SEP 和 LOCC 之间高达 12.5%的差距，这是已知的两类之间的第一个明显差距。我们的结果依赖于构建一个具有明确操作意义的可计算纠缠单调函数，与之前所有研究过的单调函数不同，它在 SEP 下不是单调的。最后，我们证明了一个有趣的事实，即 LOCC 协议的收敛序列在极限情况下不一定是 LOCC 可行的。
