Blue-light attack on IQ modulator skews key-rate estimates in CV-QKD experiment
Researchers at National University of Defense Technology and Shanghai Jiao Tong University, with the Shanghai Research Centre for Quantum Sciences and Hefei National Laboratory, experimentally tested a reversible photorefractive attack on a local-local-oscillator continuous-variable QKD system. Moderate blue-light illumination reduced the modulation variance of a lithium-niobate IQ modulator to a stable value of about 6.2 shot-noise units without sharply raising estimated excess noise. The article says this led receivers to overestimate channel transmittance and underestimate excess noise, producing a false positive key rate equivalent to 1 bit per symbol when no secure key should exist. The effect reverses gradually when illumination stops, and the article says the manipulation became harder to detect after recovery. The work is an arXiv preprint and has not yet been peer reviewed.