In QKD (Quantum Key Distribution) systems, signal integrity is paramount: the system typically transmits single photons or extremely weak pulses. Unlike classical systems, standard amplification or regeneration cannot be used since they disrupt the quantum state. Thus, channel impairments—loss, noise, and dispersion—must be managed carefully. Dispersion broadens photon wave packets, lowering temporal correlations and increasing error rates (QBER).
Recent research shows that by compensating dispersion nonlocally (i.e. manipulating only one entangled photon’s path), one can restore timing correlations, thereby boosting secure key rates. In one experiment, a 6.46 km link saw key rate jump from 6.1 bits/s to 228.3 bits/s through nonlocal compensation techniques. arxiv.org
Further, in dispersive-optics QKD (DO-QKD), theoretical work predicts that beyond certain distances, dispersion compensation becomes essential to avoid coincidence peak broadening and degraded secret key rate. In fiber links shorter than ~9 km (in G.652 fiber), the benefit of a DCM may not outweigh its insertion loss, but for longer spans, compensation tends to yield superior net key rates.
