Using spatial modes for quantum key distribution (QKD) has become highly
topical due to their infinite dimensionality, promising high information
capacity per photon. However, spatial distortions reduce the feasible secret
key rates and compromise the security of a quantum channel. In an extreme form
such a distortion might be a physical obstacle, impeding line-of-sight for
free-space channels. Here, by controlling the radial degree of freedom of a
photon's spatial mode, we are able to demonstrate hybrid high-dimensional QKD
through obstacles with self-reconstructing single photons. We construct
high-dimensional mutually unbiased bases using spin-orbit hybrid states that
are radially modulated with a non-diffracting Bessel-Gaussian (BG) profile, and
show secure transmission through partially obstructed quantum links. Using a
prepare-measure protocol we report higher quantum state self-reconstruction and
information retention for the non-diffracting BG modes as compared to
Laguerre-Gaussian modes, obtaining a quantum bit error rate (QBER) that is up
to 3 times lower. This work highlights the importance of controlling the radial
mode of single photons in quantum information processing and communication as
well as the advantages of QKD with hybrid states.Comment: Published version, 15 pages, 6 figures, 2 table
