资源环境科技发展态势分析平台

An efficient entanglement-based quantum key distribution is sent from the Micius satellite to two ground observatories 1,120 kilometres apart to establish secure quantum cryptography for the exchange ofquantum keys.

Quantum key distribution (QKD)(1-3)is a theoretically secure way of sharing secret keys between remote users. It has been demonstrated in a laboratory over a coiled optical fibre up to 404 kilometres long(4-7). In the field, point-to-point QKD has been achieved from a satellite to a ground station up to 1,200 kilometres away(8-10). However, real-world QKD-based cryptography targets physically separated users on the Earth, for which the maximum distance has been about 100 kilometres(11,12). The use of trusted relays can extend these distances from across a typical metropolitan area(13-16)to intercity(17)and even intercontinental distances(18). However, relays pose security risks, which can be avoided by using entanglement-based QKD, which has inherent source-independent security(19,20). Long-distance entanglement distribution can be realized using quantum repeaters(21), but the related technology is still immature for practical implementations(22). The obvious alternative for extending the range of quantum communication without compromising its security is satellite-based QKD, but so far satellite-based entanglement distribution has not been efficient(23)enough to support QKD. Here we demonstrate entanglement-based QKD between two ground stations separated by 1,120 kilometres at a finite secret-key rate of 0.12 bits per second, without the need for trusted relays. Entangled photon pairs were distributed via two bidirectional downlinks from the Micius satellite to two ground observatories in Delingha and Nanshan in China. The development of a high-efficiency telescope and follow-up optics crucially improved the link efficiency. The generated keys are secure for realistic devices, because our ground receivers were carefully designed to guarantee fair sampling and immunity to all known side channels(24,25). Our method not only increases the secure distance on the ground tenfold but also increases the practical security of QKD to an unprecedented level.

A set of five small molecules can induce the transformation of fibroblasts into rod photoreceptor-like cells, which can partially restore pupil reflex and visual function when transplanted into a rod degeneration mouse model.

Distributing entanglement over long distances using optical networks is an intriguing macroscopic quantum phenomenon with applications in quantum systems for advanced computing and secure communication(1,2). Building quantum networks requires scalable quantum light-matter interfaces(1) based on atoms(3), ions(4) or other optically addressable qubits. Solid-state emitters(5), such as quantum dots and defects in diamond or silicon carbide(6-10), have emerged as promising candidates for such interfaces. So far, it has not been possible to scale up these systems, motivating the development of alternative platforms. A central challenge is identifying emitters that exhibit coherent optical and spin transitions while coupled to photonic cavities that enhance the light-matter interaction and channel emission into optical fibres. Rare-earth ions in crystals are known to have highly coherent 4f-4f optical and spin transitions suited to quantum storage and transduction(11-15), but only recently have single rare-earth ions been isolated(16,17) and coupled to nanocavities(18,19). The crucial next steps towards using single rare-earth ions for quantum networks are realizing long spin coherence and single-shot readout in photonic resonators. Here we demonstrate spin initialization, coherent optical and spin manipulation, and high-fidelity single-shot optical readout of the hyperfine spin state of single Yb-171(3+) ions coupled to a nanophotonic cavity fabricated in an yttrium orthovanadate host crystal. These ions have optical and spin transitions that are first-order insensitive to magnetic field fluctuations, enabling optical linewidths of less than one megahertz and spin coherence times exceeding thirty milliseconds for cavity-coupled ions, even at temperatures greater than one kelvin. The cavity-enhanced optical emission rate facilitates efficient spin initialization and single-shot readout with conditional fidelity greater than 95 per cent. These results showcase a solid-state platform based on single coherent rare-earth ions for the future quantum internet.

Single ytterbium ion qubits in nanophotonic cavities have long coherence times and can be optically read out in a single shot, establishing them as excellent candidates for optical quantum networks.