Merging "nano", rare-earths, and nonlinear crystals: key technology for large-scale quantum networks

加拿大的经济、政治和社会福祉在很大程度上依赖于安全的电子通信，例如电子银行、电子健康、电子商务和电子政务。然而，目前的公钥密码系统依赖于关于计算复杂性的未经证实的假设，容易受到算法进步和更好的经典计算机技术的影响，并将随着量子计算机的出现而过时。因此，过去或现在编码和发送的信息的保密性，即使今天仍然得到保证，也很容易受到密码破译方面的未来改进的影响，这可能导致在记录的信息失去重要性之前对其进行充分保护的解码。量子密钥分发(QKD)使用在特定量子态中准备的单个光子作为信息载体，有望为这些问题提供最终解决方案：新技术无法破坏的安全性。然而，由于光子在传输过程中丢失，以及由于被称为不可克隆定理的量子力学的基本限制而无法使用放大器，量子密钥分发目前面临着大约200公里的距离限制。有趣的是，这一限制可以通过尚不存在的量子中继器来消除。 该发现基金启动了三个非常成功的领域-使用非线性晶体产生光子对，稀土离子掺杂晶体中的光学量子存储，以及纳米技术-的组合，其目标是为这样的量子中继器创造关键技术，并消除建造的障碍。更准确地说，我们将结合一种产生光谱多路复用纠缠光子对的新方法，一种尚未证明的对微弱信号中光子数量的无损测量，以及使用纳米结构稀土离子掺杂晶体从根本上改善光子的量子记忆。这将允许我们以一种预知的和光谱多路复用的方式创建单个光子，这些光子一个接一个地与晶体中的单个集体激发相纠缠。这一雄心勃勃但迄今尚未实现的目标与我们在整个北美大陆进行可证明的安全通信的长期目标完全一致。除了在各个职业层面培养高素质的人才并推动量子光学、量子通信和纳米技术领域的发展外，该研究项目还将确保加拿大在过去十年对量子密钥开发进行了大量投资后，在这一重要领域保持竞争力。

The economic, political, and social well-being of Canada depends crucially on secure electronic communications, e.g. for e-banking, e-health, e-commerce, and e-government. Yet, current public key crypto systems rely on unproven assumptions about computational complexity, are susceptible to algorithmic advances and better classical computer technology, and will become obsolete with the advent of the quantum computer. Hence, the secrecy of messages encoded and sent in the past or present, even if still ensured today, is vulnerable to future improvements in code breaking, which may lead to decoding of recorded messages with insufficient protection before they lose importance. Quantum key distribution (QKD), which employs individual photons prepared in specific quantum states as carriers of information, promises the ultimate solution to these problems: security that cannot be compromised by new technology. Yet, as photons get lost during transmission, and amplifiers cannot be used due to a fundamental restriction of quantum mechanics known as the no-cloning theorem, QKD currently faces a distance limit of around 200 km. Interestingly, this limit can be removed through not-yet-existing quantum repeaters. Initiating the combination of three immensely successful areas – photon pair generation using non-linear crystals, optical quantum memory in rare-earth-ion-doped crystals, and nano-technology –, the goal of this Discovery Grant is to create key technology for, and remove the impediment to building, such a quantum repeater. More precisely, we will combine a novel way of generating spectrally multiplexed entangled photon pairs, a not-yet-demonstrated non-destructive measurement of the number of photons in a weak signal, and fundamentally improved quantum memory for photons using nano-structured rare-earth-ion-doped crystals. This will allow us to create, in a heralded and spectrally multiplexed fashion, individual photons that are one by one entangled with single collective excitations in the crystal. This ambitious and so-far unaccomplished goal squarely aligns with our long-term aim of provable secure communication across the North American continent. In addition to creating highly qualified personnel at various career levels and advancing the fields of quantum optics, quantum communication and nano-technology, the research project will thus ensure that Canada, after a lot of investment into QKD during the past decade, remains competitive in this important area.