Centre for Quantum Technologies, National University of Singapore, Singapore.
Phys Rev Lett. 2012 Aug 17;109(7):070501. doi: 10.1103/PhysRevLett.109.070501. Epub 2012 Aug 16.
The ability to distribute quantum entanglement is a prerequisite for many fundamental tests of quantum theory and numerous quantum information protocols. Two distant parties can increase the amount of entanglement between them by means of quantum communication encoded in a carrier that is sent from one party to the other. Intriguingly, entanglement can be increased even when the exchanged carrier is not entangled with the parties. However, in light of the defining property of entanglement stating that it cannot increase under classical communication, the carrier must be quantum. Here we show that, in general, the increase of relative entropy of entanglement between two remote parties is bounded by the amount of nonclassical correlations of the carrier with the parties as quantified by the relative entropy of discord. We study implications of this bound, provide new examples of entanglement distribution via unentangled states, and put further limits on this phenomenon.
量子纠缠的分配能力是许多量子理论基本检验和众多量子信息协议的前提。两个遥远的当事方可以通过在载体中编码量子通信来增加它们之间的纠缠量，该载体从一方发送到另一方。有趣的是，即使交换的载体与当事方没有纠缠，纠缠也可以增加。然而，根据定义的纠缠性质，它不能在经典通信下增加，载体必须是量子的。在这里，我们表明，一般来说，两个远程当事方之间的相对纠缠熵的增加受载体与当事方之间的非经典相关性的量的限制，这种相关性由相对离差熵来量化。我们研究了这个界限的含义，提供了通过非纠缠态进行纠缠分配的新实例，并进一步限制了这种现象。
