Quantum Internet in the Sky: Vision, Challenges, Solutions, and Future Directions

TL;DR

This work envisions a Quantum Internet in the Sky by leveraging non-terrestrial platforms—LEO satellites, HAPS, and LAPS—to create a multi-layer free-space optical quantum network. It analyzes platform-specific challenges such as atmospheric turbulence, pointing stability, Doppler shifts, finite-key effects, background noise, and alignment issues, and proposes concrete design strategies including miniaturized, SWaP-optimized terminals, coarse/fine pointing, adaptive optics, polarization-frame tracking, and ground-station diversity. Through representative scenarios (LEO-to-ground, LEO-to-HAPS, and HAPS-to-LAPS) and numerical case studies, the paper demonstrates the feasibility and limitations of sky-based quantum links under realistic operational constraints. It furthermore maps a path forward with future directions in high-dimensional and multipartite quantum communications and the integration of quantum networks with sensing, computing, and intelligence (IQCSCI), aiming to deliver a fully operational Quantum Internet in the Sky with broad implications for secure communications, distributed quantum computing, and quantum-enabled sensing.

Abstract

This article envisions the concept of a ``Quantum Internet in the Sky", aiming to establish ubiquitous quantum communication links among distant nodes via free-space optical channels. Our key focus is on deploying quantum communication terminals on non-terrestrial platforms, specifically unmanned aerial vehicles and satellites, at various altitudes. By highlighting the unique characteristics of these platforms compared to terrestrial counterparts, we address inherent challenges and discuss potential solutions through meticulous system designs and analyses of typical non-terrestrial quantum communication scenarios. Finally, we illuminate the path forward by proposing essential future directions that underscore the integration of high-dimensional multipartite quantum communications with sensing, computing, and intelligence for multiple users en route to realizing a fully operational Quantum Internet.

Figures (4)

• Figure 1: Overview concept of the "Quantum Internet in the Sky".
• Figure 2: Secret-key length of a decoy-state efficient BB84 QKD protocol with finite-key effects for a LEO satellite-to-HAPS downlink at 810 nm.
• Figure 3: Fidelity of a HAPS-to-LAPS downlink entanglement transmission as a function of spectral irradiance at 810 nm under various PE levels.
• Figure 4: Greenwood frequency and Fried coherence length versus zenith angle for a LEO satellite-to-ground downlink at 1550 nm and 810 nm.