Free-Space Quantum Communication with a Portable Quantum Memory

Abstract

The realization of an elementary quantum network that is intrinsically secure and operates over long distances requires the interconnection of several quantum modules performing different tasks. In this work we report the interconnection of four different quantum modules: (i) a random polarization qubit generator, (ii) a free-space quantum communication channel, (iii) an ultra-low noise portable quantum memory and (iv) a qubit decoder, in a functional elementary quantum network possessing all capabilities needed for quantum information distribution protocols. We create weak coherent pulses at the single photon level encoding polarization states $|H\rangle, |V\rangle, |D\rangle, |A\rangle$ in a randomized sequence. The random qubits are sent over a free-space link and coupled into a dual rail room temperature quantum memory and after storage and retrieval are analyzed in a four detector polarization analysis akin to the requirements of the BB84 protocol. We also show ultra-low noise and fully-portable operation, paving the way towards memory assisted all-environment free space quantum cryptographic networks.