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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Adaptive Optics Enabled Entanglement Distribution Over Atmospheric Turbulence Channels

Vijay Nafria, Ivan B. Djordjević

Published Jun 26, 2023• 2 citations
Publisher

Abstract

Entanglement is key quantum information processing feature enabling quantum communication, networking, and sensing [1]. Unfortunately, long-distance quantum communication is affected by the photon loss, given that quantum signals cannot be amplified. As an alternative, free-space optical (FSO) links can be used instead for entanglement distribution. However, the FSO links are severely affected by atmospheric turbulence effects, in addition to scattering effects. In this paper, we demonstrate that adaptive optics [2] is a useful tool to improve fidelity of entanglement when entangled states are distributed over turbulent FSO links. We present results from our FSO communication experiment where we generated entangled photons pairs, launched them into free-space, and later collected them for coincidence count measurement. We demonstrate that adaptive optics can be used to make improvements in coincidence counts.

DOI
10.1109/cleo/europe-eqec57999.2023.10232247

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Entanglement is key quantum information processing feature enabling quantum communication, networking, and sensing [1]. Unfortunately, long-distance quantum communication is affected by the photon loss, given that quantum signals cannot be amplified. As an alternative, free-space optical (FSO) links can be used instead for entanglement distribution. However, the FSO links are severely affected by atmospheric turbulence effects, in addition to scattering effects. In this paper, we demonstrate that adaptive optics [2] is a useful tool to improve fidelity of entanglement when entangled states are distributed over turbulent FSO links. We present results from our FSO communication experiment where we generated entangled photons pairs, launched them into free-space, and later collected them for coincidence count measurement. We demonstrate that adaptive optics can be used to make improvements in coincidence counts.
In this paper, we present our experiment results demonstrating multi-wavelength entanglement distribution over the turbulent outdoor free-space optical (FSO) link we established at the University of Arizona. We generated with the help of PPLN waveguide, C-band laser diode, and an EDFA entangled photon pairs, transmitted them over the turbulent FSO link, separated different wavelength channels with coarse WDM demultiplexers, and measured the coincidence counts of four wavelength channels with the help of correlated photon detection system. To improve the system tolerance to turbulence effects we use adaptive optics (AO) and demonstrate that the AO can be used to increase the coincidence counts.
Quantum Key Distribution (QKD) promises a provably secure method to transmit information from one party to another. Free-space QKD allows for this information to be sent over great distances and in places where fibre-based communications cannot be implemented, such as ground-satellite. The primary limiting factor for free-space links is the effect of atmospheric turbulence, which can result in significant error rates and increased losses in QKD channels. Here, we employ the use of a high-speed Adaptive Optics (AO) system to make real-time corrections to the wavefront distortions on spatial modes that are used for high-dimensional QKD in our turbulent channel. First, we demonstrate the effectiveness of the AO system in improving the coupling efficiency of a Gaussian mode that has propagated through turbulence. Through process tomography, we show that our system is capable of significantly reducing the crosstalk of spatial modes in the channel. Finally, we show that employing AO reduces the quantum dit error rate for a high-dimensional orbital angular momentum-based QKD protocol, allowing for secure communication in a channel where it would otherwise be impossible. These results are promising for establishing long-distance free-space QKD systems. High-dimensional quantum key distribution will allow for higher information density and greater error tolerance in future quantum networks. This work experimentally demonstrates how implementing an adaptive optics system in a spatial-mode free-space optical link can allow for quantum communications where it would otherwise be impossible.