Characterization and mitigation of information loss in a six-state quantum-key-distribution protocol with spatial modes of light through turbulence

摘要

Quantum communication with structured photons is topical, owing to the multidimensional state space of spatial modes. However, spatial modes are fragile and their quality degrades when perturbed in traditional communication media such as free-space and optical fibers. Here, we illustrate the effects of atmospheric turbulence on a six-state quantum-key-distribution protocol with orbital angular momentum (OAM) modes. We experimentally characterize the fidelity decay as a function of turbulence strength, showing a concomitant decrease with increasing perturbation, and consider the influence of both mode order and mode size, showing that OAM modes with higher helicity are more resilient to turbulence for this protocol.We outline two approaches to mitigate the photon information loss. In the first, we show that by postselecting on a high-dimensional subspace at the detection side, we can recover information contained in the scattered modes. In the second, we measure the channel operator by means of classically entangled light and mitigate errors on the quantum state through entanglement concentration by means of one-party Procrustean filtering. The tools we provide here will be beneficial for realizing more robust quantum communication with OAM modes of light.