Performance Analysis of Free-space Quantum Key Distribution Using Multiple Spatial Modes

Abstract

In the diffraction-limited near-field propagation regime, free-space optical quantum key distribution (QKD) systems can employ multiple spatial modes to improve their key rate. Here, we analyze QKD using the non-orthogonal flat-top focused beams. Although they suffer from a rate penalty, their ease of implementation make them an attractive alternative to the well-studied orthonormal Laguerre-Gauss (LG) modes. Indeed, in the presence of turbulence, the non-orthogonal modes may achieve higher QKD rate than the LG modes.

Detecting Orbital Angular Momentum of Light in Satellite-to-Ground Quantum Communications

“…It has been discussed (in e.g., [30]) that the channel's power-transfer behavior has far-field and near-field regimes that are characterized by the Fresnel number product 𝐷 f = 𝐴 T 𝐴 R /(𝜆𝐿) 2 with 𝐴 T (𝐴 R ) being the transmitter (receiver) aperture area. Specifically, the near-field regime is defined by 𝐷 f 1 and the far-field regime is defined by 𝐷 f 1.…”