Física Teòrica, Informació i Fenòmens Quàntics, Departament de Física, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain.
Phys Rev Lett. 2010 Aug 20;105(8):080504. doi: 10.1103/PhysRevLett.105.080504. Epub 2010 Aug 18.
We provide rigorous, efficiently computable and tight bounds on the average error probability of multiple-copy discrimination between qubit mixed states by local operations assisted with classical communication (LOCC). In contrast with the pure-state case, these experimentally feasible protocols perform strictly worse than the general collective ones. Our numerical results indicate that the gap between LOCC and collective error rates persists in the asymptotic limit. In order for LOCC and collective protocols to achieve the same accuracy, the former can require up to twice the number of copies of the latter. Our techniques can be used to bound the power of LOCC strategies in other similar settings, which is still one of the most elusive questions in quantum communication.
我们通过局域操作和经典通讯（LOCC）为量子比特混合态的多拷贝分辨提供了严格、高效计算和紧的平均错误概率界。与纯态情况不同，这些实验上可行的协议表现严格劣于一般的集体协议。我们的数值结果表明，LOCC 和集体误差率之间的差距在渐近极限中仍然存在。为了使 LOCC 和集体协议达到相同的精度，前者可能需要后者的两倍多的副本。我们的技术可以用于在其他类似的情况下限制 LOCC 策略的能力，这仍然是量子通信中最难以捉摸的问题之一。
