Impact of Turbulence in Long Range Quantum and Classical Communications

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.

Figure 1

Schematic of the optical setup. DM: dichroic mirror.

Figure 2

SPAD temporal distribution of count occurrences and corresponding lognormal and Mandel curves. We can compare the data with the corresponding Poissonian distribution with the same mean value ($234.1\pm 0.1$) that would be obtained without turbulence.

Figure 3

Photodiode temporal distribution intensity occurrences and corresponding lognormal curve.

Figure 4

SPAD power spectrum and cumulative power spectrum. Frequency bound (red vertical line): The frequencies below 51 Hz contribute to 95% of the scintillation index.

Figure 5

Duration (in milliseconds) of events with overthreshold counting. In the different plots we considered a threshold of 1, 2, 4, and 6 dB above the average.

Figure 6

SNR and the percentage of the overall counts that will be detected in the function of the threshold selection.