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

点击翻译按钮获取中文摘要

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.