Demonstration of single-shot microwave quantum key distribution

Quantum key distribution (QKD) promises to deliver unconditionally secure distribution of classical keys between remote parties. So far, its implementation in the microwave regime, a regime of high interest due to its frequency compatibility with superconducting quantum circuits, has been missing. Here, we present an experimental realization of a continuous-variable QKD protocol using propagating displaced squeezed microwave states and demonstrate an experimental unconditional security. We show that secret key rates can be noticeably increased by adding trusted noise to the preparation side. Our results indicate a feasibility of secure microwave quantum communication under cryogenic (up to 1200 meters) and open-air (up to 80 meters) conditions. Finally, we discuss storage of squeezed microwave states in spin ensembles, enabling the usage of microwave quantum memories in our communication protocol.