Enhancing secure key rates of satellite QKD using a quantum dot\n single-photon source

Global quantum secure communication can be achieved using quantum key\ndistribution (QKD) with orbiting satellites. Established techniques use\nattenuated lasers as weak coherent pulse (WCP) sources, with so-called\ndecoy-state protocols, to generate the required single-photon-level pulses.\nWhile such approaches are elegant, they come at the expense of attainable final\nkey due to inherent multi-photon emission, thereby constraining secure key\ngeneration over the high-loss, noisy channels expected for satellite\ntransmissions. In this work we improve on this limitation by using true\nsingle-photon pulses generated from a semiconductor quantum dot (QD) embedded\nin a nanowire, possessing low multi-photon emission ($<10^{-6}$) and an\nextraction system efficiency of -15 dB (or 3.1%). Despite the limited\nefficiency, the key generated by the QD source is greater than that generated\nby a WCP source under identical repetition rate and link conditions\nrepresentative of a satellite pass. We predict that with realistic improvements\nof the QD extraction efficiency to -4.0 dB (or 40%), the quantum-dot QKD\nprotocol outperforms WCP-decoy-state QKD by almost an order of magnitude.\nConsequently, a QD source could allow generation of a secure key in conditions\nwhere a WCP source would simply fail, such as in the case of high channel\nlosses. Our demonstration is the first specific use case that shows a clear\nbenefit for QD-based single-photon sources in secure quantum communication, and\nhas the potential to enhance the viability and efficiency of satellite-based\nQKD networks.\n