Title: A Four-Round LOCC Protocol Outperforms All Two-Round Protocols in Reducing the Entanglement Cost for A Distributed Quantum Information Processing Show Chinese title

Title: 一个四轮LOCC协议在减少分布式量子信息处理的纠缠成本方面优于所有两轮协议

Abstract: We prove that there is a trade-off relation between the entanglement cost and the number of rounds of communication, for two distant parties to accomplish a bidirectional quantum information task by local operations and classical communication (LOCC). We consider an implementation of a class of two-qubit controlled-unitary gate by LOCC assisted by shared entanglement, in an information theoretical scenario of asymptotically many input pairs and vanishingly small error. We prove the trade-off relation by showing that one ebit of entanglement per pair is necessary to be consumed for implementing the unitary by any two-round protocol, whereas the entanglement cost by a four-round protocol is strictly smaller than one ebit per pair. Show Chinese abstract

Abstract: 我们证明了，在两个远程参与方通过局域操作和经典通信（LOCC）完成双向量子信息任务时，纠缠代价与通信轮次数之间存在权衡关系。 我们在渐近无穷多输入对且误差趋于零的信息理论场景下，考虑了一类两比特受控幺正门的LOCC实现，其中借助共享纠缠辅助实现。 我们通过证明以下内容来证明这种权衡关系：对于任意两轮协议，每对输入需要消耗一比特纠缠才能实现该幺正操作；而对于四轮协议，每对输入的纠缠代价严格小于一比特。