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.

Quantum mechanics governs the microscopic world, where low mass and momentum reveal a natural wave-particle duality. Magnifying quantum behaviour to macroscopic scales is a major strength of the technique of cooling and trapping atomic gases, in which low momentum is engineered through extremely low temperatures. Advances in this field have achieved such precise control over atomic systems that gravity, often negligible when considering individual atoms, has emerged as a substantial obstacle. In particular, although weaker trapping fields would allow access to lower temperatures(1,2), gravity empties atom traps that are too weak. Additionally, inertial sensors based on cold atoms could reach better sensitivities if the free-fall time of the atoms after release from the trap could be made longer(3). Planetary orbit, specifically the condition of perpetual free-fall, offers to lift cold-atom studies beyond such terrestrial limitations. Here we report production of rubidium Bose-Einstein condensates (BECs) in an Earth-orbiting research laboratory, the Cold Atom Lab. We observe subnanokelvin BECs in weak trapping potentials with free-expansion times extending beyond one second, providing an initial demonstration of the advantages offered by a microgravity environment for cold-atom experiments and verifying the successful operation of this facility. With routine BEC production, continuing operations will support long-term investigations of trap topologies unique to microgravity(4,5), atom-laser sources(6), few-body physics(7,8)and pathfinding techniques for atom-wave interferometry(9-12).

Environmental change is rapidly accelerating, and many species will need to adapt to survive(1). Ensuring that protected areas cover populations across a broad range of environmental conditions could safeguard the processes that lead to such adaptations(1-3). However, international conservation policies have largely neglected these considerations when setting targets for the expansion of protected areas(4). Here we show that-of 19,937 vertebrate species globally(5-8)-the representation of environmental conditions across their habitats in protected areas (hereafter, niche representation) is inadequate for 4,836 (93.1%) amphibian, 8,653 (89.5%) bird and 4,608 (90.9%) terrestrial mammal species. Expanding existing protected areas to cover these gaps would encompass 33.8% of the total land surface-exceeding the current target of 17% that has been adopted by governments. Priority locations for expanding the system of protected areas to improve niche representation occur in global biodiversity hotspots(9), including Colombia, Papua New Guinea, South Africa and southwest China, as well as across most of the major land masses of the Earth. Conversely, we also show that planning for the expansion of protected areas without explicitly considering environmental conditions would marginally reduce the land area required to 30.7%, but that this would lead to inadequate niche representation for 7,798 (39.1%) species. As the governments of the world prepare to renegotiate global conservation targets, policymakers have the opportunity to help to maintain the adaptive potential of species by considering niche representation within protected areas(1,2).

Protected areas would need to expand to 33.8% of the total land surface to adequately represent environmental conditions across the habitats of amphibians, birds and terrestrial mammals, far exceeding the current 17% target.