Azuma Koji, Tamaki Kiyoshi, Lo Hoi-Kwong
NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato Wakamiya, Atsugi, Kanagawa 243-0198, Japan.
Center for Quantum Information and Quantum Control, Department of Physics and Department of Electrical and Computer Engineering, University of Toronto, Toronto, Ontario, Canada M5S 3G4.
Nat Commun. 2015 Apr 15;6:6787. doi: 10.1038/ncomms7787.
Quantum communication holds promise for unconditionally secure transmission of secret messages and faithful transfer of unknown quantum states. Photons appear to be the medium of choice for quantum communication. Owing to photon losses, robust quantum communication over long lossy channels requires quantum repeaters. It is widely believed that a necessary and highly demanding requirement for quantum repeaters is the existence of matter quantum memories. Here we show that such a requirement is, in fact, unnecessary by introducing the concept of all-photonic quantum repeaters based on flying qubits. In particular, we present a protocol based on photonic cluster-state machine guns and a loss-tolerant measurement equipped with local high-speed active feedforwards. We show that, with such all-photonic quantum repeaters, the communication efficiency scales polynomially with the channel distance. Our result paves a new route towards quantum repeaters with efficient single-photon sources rather than matter quantum memories.
量子通信有望实现秘密信息的无条件安全传输以及未知量子态的可靠转移。光子似乎是量子通信的首选媒介。由于光子损耗，在长距离有损信道上实现稳健的量子通信需要量子中继器。人们普遍认为，量子中继器的一个必要且极具挑战性的要求是存在物质量子存储器。在此，我们通过引入基于飞行量子比特的全光量子中继器概念表明，这样的要求实际上并非必要。特别是，我们提出了一种基于光子簇态机枪和配备局部高速有源前馈的容错测量的协议。我们表明，借助此类全光量子中继器，通信效率随信道距离呈多项式增长。我们的结果为采用高效单光子源而非物质量子存储器的量子中继器开辟了一条新途径。
