Experimental Evaluation of the Impact of Turbulence on a Time-Bin and Phase QKD System

Abstract

The time-bin and phase bases for quantum key distribution (QKD) schemes have been explored as an alternative to polarization bases to overcome the challenge of optical fiber birefringence. However, in free-space, turbulence introduces perturbations in the optical phase and path-length that might influence the performance of these QKD systems. We conducted an experiment employing a pair of commercial QKD modules utilizing the time-bin and phase bases to implement the BB84 protocol. Our results indicate that the impact of turbulence on these QKD systems may extend beyond intensity fluctuations, degrading the quantum bit error rate (QBER) as the turbulence strength increases. We report the results of our experiment, where, under strong turbulence, a difference of 1.3595 times the standard deviation was obtained between the measured and estimated QBER due to statistical effects, indicating the presence of additional error sources. Subsequently, an estimated increase in the probability of hitting the wrong detector of $0.20\pm 0.04$ % per decade of the refractive index structure parameter was estimated, with a p-value of $8.27\cdot 10^{-20}$ for the hypothesis test with the null-hypothesis being that the probability of hitting the wrong detector does not depend on the turbulence severity.