Impact of Turbulence in Long Range Quantum and Classical Communications

Abstract

The study of the free-space distribution of quantum correlations is necessary for any future application of quantum and classical communication aiming to connect two remote locations. Here we study the propagation of a coherent laser beam over 143 km (between Tenerife and La Palma Islands of the Canary archipelagos). By attenuating the beam we also studied the propagation at the single photon level. We investigated the statistic of arrival of the incoming photons and the scintillation of the beam. From the analysis of the data, we propose the exploitation of turbulence to improve the signal to noise ratio of the signal.

Adaptive real time selection for quantum key distribution in lossy and turbulent free-space channels

“…As demonstrated in Ref. [24], the statistics of the transmission of a long free-space channel follows a log-normal distribution. The measured probe voltage at the receiver, being the transmitted intensity con stant, follows the same distribution, given by p(V\mv ,cr2) = -y=^-yexp{ -[(In 2X + 4CT2)]2/(2er2)}.…”

“…2. According to the theory [24,28], the probabilities follow a log-normal distribution, as demonstrated by the continuous (red) curve representing the log-normal fit.…”

“…The temporal profile of the transmissivity in a long and strongly turbulent channel has characteristic peaks lasting few milliseconds, and following a lognormal distribution [24]. On these grounds, we will introduce and demonstrate an adaptive real time selection (ARTS) scheme, inspired by the experimen tal observations reported in Ref.…”

Turbulent single-photon propagation in the Canary optical link

“…4 a million laser pulses in the quantum communication implementation [1,5]. Therefore, the effect of turbulence is here found to provide a noticeable fraction of the link time with a significant lower-than-average optical losses.…”

Random bits, true and unbiased, from atmospheric turbulence

“…To implement our method in a proof of concept demonstrator, we have chosen a very long free space channel used in the last years for experiments in Quantum Communications at the Canary Islands18192021. Here, after a propagation of 143 km at an altitude of the terminals of about 2400 m, the turbulence in the path is converted into a dynamical speckle at the receiver.…”