Quantum key distribution (QKD) uses individual light quanta in quantum superposition states to guarantee unconditional communication security between distant parties. However, the distance over which QKD is achievable has been limited to a few hundred kilometres, owing to the channel loss that occurs when using optical fibres or terrestrial free space that exponentially reduces the photon transmission rate. Satellite-based QKD has the potential to help to establish a global-scale quantum network, owing to the negligible photon loss and decoherence experienced in empty space. Here we report the development and launch of a low-Earth-orbit satellite for implementing decoy-state QKD-a form of QKD that uses weak coherent pulses at high channel loss and is secure because photon-number-splitting eavesdropping can be detected. We achieve a kilohertz key rate from the satellite to the ground over a distance of up to 1,200 kilometres. This key rate is around 20 orders of magnitudes greater than that expected using an optical fibre of the same length. The establishment of a reliable and efficient space-to-ground link for quantum-state transmission paves the way to global-scale quantum networks.
While
catalysis is highly dependent on the electronic structure
of the catalyst, the understanding of catalytic performance affected
by electron spin regulation remains challenging and rare. Herein,
we have developed a facile strategy to the manipulation of the cobalt
spin state over covalent organic frameworks (COFs), COF-367-Co, by
simply changing the oxidation state of Co centered in the porphyrin.
Density functional theory (DFT) calculations together with experimental
results confirm that CoII and CoIII are embedded
in COF-367 with S = 1/2 and 0 spin ground states,
respectively. Remarkably, photocatalytic CO2 reduction
results indicate that COF-367-CoIII exhibits favorable
activity and significantly enhanced selectivity to HCOOH, accordingly
much reduced activity and selectivity to CO and CH4, in
sharp contrast to COF-367-CoII. The results highlight that
the spin-state transition of cobalt greatly regulates photocatalytic
performance. Theoretical calculations further disclose that the presence
of CoIII in COF-367-Co is preferable to the formation of
HCOOH but detrimental to its further conversion, which clearly accounts
for its distinctly different photocatalysis over COF-367-CoII. To the best of our knowledge, this is the first report on regulating
photocatalysis by spin state manipulation in COFs.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.