两个平行或反平行自旋的集体测量与局部测量
Collective versus local measurements on two parallel or antiparallel spins
摘要：
我们给出了一个完整的分析，两个自旋的协变测量。我们考虑两个平行和两个反平行自旋的情况下，我们认为这两个自旋的集体测量，测量只需要本地量子操作和经典通信（LOCC）。在所有的情况下，我们得到的最佳测量任意的结晶度。特别是，我们表明，如果目标是尽可能确定自旋指向的方向，最好是在反平行自旋上进行测量（如Gisin和Popescu所示），其次是在平行自旋上进行测量，最差的是限制在LOCC测量。如果目标是尽可能确定与自旋指向正交的方向，最好对平行自旋进行测量，而对反平行自旋的测量和LOCC测量都不太好，但等效。
英文摘要：
We give a complete analysis of covariant measurements on two spins. We consider the cases of two parallel and two antiparallel spins, and we consider both collective measurements on the two spins, and measurements which require only Local Quantum Operations and Classical Communication (LOCC). In all cases we obtain the optimal measurements for arbitrary fidelities. In particular we show that if the aim is determine as well as possible the direction in which the spins are pointing, it is best to carry out measurements on antiparallel spins (as already shown by Gisin and Popescu), second best to carry out measurements on parallel spins and worst to be restricted to LOCC measurements. If the the aim is to determine as well as possible a direction orthogonal to that in which the spins are pointing, it is best to carry out measurements on parallel spins, whereas measurements on antiparallel spins and LOCC measurements are both less good but equivalent.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
