Fully autocompensating high-dimensional quantum cryptography by quantum degenerate four-wave mixing
Jesús Liñares, Xesús Prieto-Blanco, Daniel Balado, Gabriel M. Carral · Physical Review A · 2021
We present a communication system based on quantum degenerate four-wave mixing for achieving fully autocompensating high-dimensional quantum cryptography. We prove that random phase shifts and couplings (cross-talking) among $2N$ optical modes (spatial and polarization modes), represented by arbitrary $\mathrm{SU}(2N)$ transformations and due to mechanical and thermal perturbations, imperfections, and so on, are autocompensated after a single round trip between Alice and Bob. Bob uses a source of single photons or, alternatively, attenuated coherent states and thus autocompensated 1-qudit states are received by Bob for using them with high-dimensional quantum key distribution (QKD) protocols that provide larger secret key rates for large $N$. A security study is also presented for this autocompensating quantum cryptography system, where it is found that the secure key rate increases with respect to nonautocompensated links for decoy-state QKD in the case of collective attacks. This plug-and-play system can be used in both optical fiber and free-space communication systems.