More than 15 months after? landing in Jezero Crater on Mars , NASA’s Perseverance rover has finally begun its hunt for ancient life in earnest. On 28 May, Perseverance ground a 5-centimetre-wide circular patch into a rock at the base of what was once a river delta in the crater. This delta formed billions of years ago, when a long-vanished river deposited layers of sediment into Jezero, and it is? the main reason that NASA sent the rover there . On Earth, river sediment is usually te...

1. Introduction . Since the beginning of the 21st century, clock synchronization schemes based on quantum entanglement and compressed states have been widely investigated because of their improvement in accuracy and potential applications in secure clock transfer. In terms of clock accuracy, the number-squeezed states $\left n\right \rangle$ in the $m$ -fold entangled state can enhance the accuracy limit by $\sqrt {mn}$ times [ 1 ]. For the security of clock transfer, the non-local...