Quantum key distribution (QKD) can be used to produce a cryptographic key whose security is unconditionally guaranteed by quantum mechanics. The range of fiber-based QKD links is limited, by loss, to a few hundred kilometers, and cannot be used between mobile platforms. Free space QKD can, in principle, overcome these limitations. In practice, very narrow beam divergences must be used, requiring highly accurate pointing of the transmitting terminal to the receiver. This makes deployment very difficult. Here we describe an entirely new type of free space QKD link, using modulating retro-reflectors (MRR). The MRR-QKD link eases the pointing requirements A laboratory-based BB84 QKD link using multiple quantum well MRRs is demonstrated, and link budgets for possible applications are discussed.
William S. Rabinovich, Rita Mahon, Mike S. Ferraro, Peter G. Goetz, Mark Bashkansky, Rachel E. Freeman, James L. Murphy, and John Reintjes, "A BB84 free space quantum key distribution link implemented with modulating retro-reflectors," Proc. SPIE 10524, Free-Space Laser Communication and Atmospheric Propagation XXX, 105240N (Presented at SPIE LASE: January 30, 2018; Published: 15 February 2018); https://doi.org/10.1117/12.2297637.
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