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arXiv · 2606.04947

Phase-correlation-free quantum key distribution source operating at gigahertz rates

Shashank Kumar·Alessandro Marcomini·Loïc Millet·Towsif Taher·Aurélien Cavalié·Raphael Houlmann·David Cabrerizo·Gianluca Boso·Marcos Curty·Rob Thew·Boris Korzh
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Abstract

Phase randomization is essential for the security of practical decoy-state quantum key distribution (QKD) systems. Commonly, implementations rely on laser sources which are either actively phase-randomized, or gain-switched. However, at high repetition rates these show correlations, which can ultimately compromise security and performance. We present a 1.25 GHz phase-randomized QKD source based on a super-luminescent light emitting diode (SLED) operating in the C-band as a compact and cost-effective alternative. The source generates $\sim100$ ps optical pulses with $400$ ps pulse-to-pulse separation, compatible with high-speed time-bin encoding. Interferometric measurements demonstrate $>99\%$ visibility between adjacent time bins, confirming strong first-order coherence within the same quantum signals, while the spontaneous-emission-driven nature of the SLED ensures intrinsic global phase randomization between adjacent signals. This work establishes a scalable SLED-based platform for high-speed prepare-and-measure QKD systems.

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Shashank Kumar, Alessandro Marcomini, Loïc Millet, Towsif Taher, Aurélien Cavalié, Raphael Houlmann, David Cabrerizo, Gianluca Boso, Marcos Curty, Rob Thew, Boris Korzh. 2026-06-03. Phase-correlation-free quantum key distribution source operating at gigahertz rates. https://doi.org/10.1063/5.0347954

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