Quantum key distribution with entangled photons generated on demand by a quantum dot

Abstract

Quantum key distribution—exchanging a random secret key relying on a quantum mechanical resource—is the core feature of secure quantum networks. Entanglement-based protocols offer additional layers of security and scale favorably with quantum repeaters, but the stringent requirements set on the photon source have made their use situational so far. Semiconductor-based quantum emitters are a promising solution in this scenario, ensuring on-demand generation of near-unity-fidelity entangled photons with record-low multiphoton emission, the latter feature countering some of the best eavesdropping attacks. Here, we use a coherently driven quantum dot to experimentally demonstrate a modified Ekert quantum key distribution protocol with two quantum channel approaches: both a 250-m-long single-mode fiber and in free space, connecting two buildings within the campus of Sapienza University in Rome. Our field study highlights that quantum-dot entangled photon sources are ready to go beyond laboratory experiments, thus opening the way to real-life quantum communication.

Entanglement-based quantum key distribution with a blinking-free quantum dot operated at a temperature up to 20 K

“…18 This allowed the demonstration of entanglement-based QKD with a QBER as low as 1.9%. 16,19 Independent of the QD materials used, the best performances in terms of entanglement fidelity and biexciton state-preparation efficiency have been obtained by operating the QD sources at temperatures below 10 K and using the resonant two-photonexcitation (TPE) condition. 20,21 One of the drawbacks of the very low working temperatures is that they are difficult to achieve in satellites, where strong payload restrictions have to be met.…”

Quantum Communication Using Semiconductor Quantum Dots

“…The last type of QD‐device that shall be mentioned here was used for a recent implementation of entanglement‐based QKD experiments [ 202,203 ] and utilized optically pumped symmetric GaAs QDs grown by the droplet‐etching method (Figure 4d). Featuring short radiative lifetimes and small FSSs, these QDs enable large entanglement fidelities, [ 107 ] while reaching out‐coupling efficiencies of about 8% if combined with a solid immersion lens.…”

“…Recently, two other successful implementations of entanglement based‐QKD were reported. [ 202,203 ] Both experiments used the same type of optically excited QD‐source, comprising a GaAs QD fabricated by the droplet‐etching technique (cf. Figure 4d) embedded between a bottom DBR and a solid immersion lens on top.…”

“…Basso Basset et al. [ 202 ] realized a fiber link (250 m) as well as a free‐space link (270 m) with comparable transmission lengths, allowing for a direct comparison of both channel types operated with the same QD‐source (Figure 12b). The authors observed better performance in terms of larger Bell parameters and fewer fluctuations for the entanglement distribution via the fiber‐based link, as seen in Figure 12e.…”

“…Basso Basset et al. used an asymmetric Ekert protocol [ 202 ] to perform QKD between two buildings b) and the photons were transmitted both through an optical fiber (top panel in e) and a free‐space (bottom panel in e) and the degree of entanglement (second column in e) and the key rate (third column in e) were compared. (a,c,d) Reproduced under the terms of the Creative Commons CC‐BY license.…”