Reconfigurable metasurfaces to realize BB84 protocol for wireless quantum communication.

Metasurfaces showcase unique abilities to arbitrarily manipulate the amplitude, phase, and polarization of electromagnetic (EM) waves, facilitating their application in wireless communication. In the propagation of EM waves, traditional methods cause severe security concerns in channel/deciphering under eavesdropping. Fortunately, quantum communication, based on quantum key distribution (QKD) of the BB84 protocol, endows the transmission with high security. However, the conventional QKD technology relies on complicated manipulation of a single photon and is prone to channel collapses once an eavesdropper intervenes. Furthermore, the merit of the BB84 protocol has not been realized in metasurfaces as a transmission channel. Here, we, for the first time as far as we know, used metasurfaces to implement wireless transmission of quantum information via the first QKD protocol, BB84. These metasurfaces provided four conjugated quantum states to concretely demonstrate the BB84 protocol through a conveyor-type switching method. High-fidelity holographic results were obtained at ∼10 GHz and beyond in both experiment and simulation. As compared with traditional QKD technology, our BB84 protocol based on metasurfaces is more stable and secure in information transmission. In addition, the metasurfaces have electromechanical switchable mode, empowering them to have multidisciplinary functions in wireless communication, e.g., program-controlled antennas, intelligent reflectors, and variable metalens.