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By using Rb vapor filters, free-space quantum key distribution with the B92 protocol was realized experimentally; the filters based on the Faraday anomalous dispersion effect were used to suppress strong background light. With these atomic filters as spectral filtering, average transmission rates of sifted keys and corrected keys have reached as high as 3.14 and 1.56kbits∕s, respectively, while the error rate was maintained at a reasonable low level of 5.10%. The experimental results show that our Rb vapor filters with transmission efficiency of around 60% operate well under the condition of the mean photon number n¯⩽0.1.

No abstract

Interference usually occurs between two non-orthogonally polarized light beams. Hence, metasurface enabled polarization multiplexing is generally conducted under two orthogonal polarization states to realize independent intensity and/or phase modulations. Herein, we show that polarization multiplexed metasurfaces can work under three non-orthogonal polarization states to realize tri-channel image displays with independent information encoding. Specifically, enabled by orientation degeneracy, each nanostructure of the metasurface operates with triple-manipulations of light, i.e., two channels for independent intensity manipulation under π/4 and 3π/8 linearly polarized (LP) light, respectively, and one channel for phase manipulation without polarization control. We experimentally demonstrate this concept by recording one continuous-brightness polychromatic image and one binary-brightness polychromatic image right at the metasurface plane, while a continuous-brightness polychromatic image is reconstructed in the far field, corresponding to three independent channels, respectively. More interestingly, in another design strategy with separated image encoding of two wavelengths, up to six independent image-display channels can be established and information delivery becomes safer by utilizing encryption algorithms. With the features of high information capacity and high security, the proposed meta-devices can empower advanced research and applications in multi-channel image displays, orbital angular momentum multiplexing communication, information encryption, anti-counterfeiting, multifunctional integrated nano-optoelectronics, etc.