Quantum relay boosts free-space optical communication with energy harvesting
Time-Switching Energy-Harvesting Quantum Relay-Assisted FSO Communication with Displaced Squeezed Signaling
Information Theory
Summary
Communicating with lasers through the air can be tricky because the atmosphere distorts the signal. This paper studies a system that uses a quantum relay powered by harvesting light to help send messages more reliably over free space optics. The relay uses a special kind of quantum signal called displaced squeezed signaling to improve performance. The authors analyze how atmospheric turbulence affects this setup and show when using squeezed signals helps reduce errors. They also find the best way to balance energy harvesting and data throughput for this system.
What this means in practice
- •For optical communication engineers: Design relay systems that harvest energy from light and use quantum signaling to improve free-space optical links under turbulent conditions.
- •For quantum hardware developers: Develop quantum relays that optimize photon use and signal squeezing to increase communication reliability in network nodes powered by optical energy harvesting.
Authors
Nizar Khalfet, Francisco A. Monteiro, Ioannis Krikidis
Abstract
This paper investigates a quantum relay-assisted free-space optical (FSO) communication system in which a decode-and-forward relay is powered by time-switching optical energy harvesting and forwards the decoded information using displaced squeezed signaling (DSS). To obtain a physically con sistent description of turbulence-induced loss for non-classical signaling, each hop is modeled as a pure-loss bosonic chan nel whose random transmissivity follows a truncated Gamma Gamma law, i.e., the Gamma-Gamma irradiance conditioned on the physically admissible range of a transmittance. Under this channel, coherent states remain pure, whereas squeezed states are mapped to mixed Gaussian states. Under Helstrom-optimal detection, the average error of the coherent hop is derived in exact Laplace-series form. For the DSS hop, we derive the output states, a closed-form Gaussian fidelity with rigorous two sided bounds on the Helstrom error, and prove the existence of a loss-aware optimal photon partition. Furthermore, we prove that optimized squeezing preserves both the turbulence-induced diversity order and the leading asymptotic constant of coherent relaying, so that its benefit is a finite-photon-budget effect, and that an interior throughput-optimal harvesting fraction exists. A covariance-preserving benchmark with an exact series representation yields an analytical upper bound on the achievable throughput whose absolute gap vanishes as the relay photon budget grows. Numerical results based on the exact mixed-state Helstrom error quantify the benefit of squeezing and the regime in which it is useful.