Entanglement Distribution Via Satellite Achieves Continental-Scale (km) Communication with High Fidelity

Distributing entanglement over long distances represents a fundamental challenge in building a future quantum internet, and researchers are actively exploring satellite-based solutions to overcome the limitations of fibre optic cables. Nicholas Zaunders and Timothy Ralph, from the Centre for Quantum Computation and Communication Technology at the University of Queensland, investigate the feasibility of two distinct network architectures for distributing entanglement, a network connecting multiple satellites and another linking ground stations via a satellite, and evaluate competing protocols for achieving this. Their work establishes clear performance benchmarks for different entanglement distribution schemes, considering both discrete and continuous variable quantum resources and the potential benefits of advanced techniques like noiseless linear amplification. By modelling realistic free-space optical channels, including atmospheric turbulence, the team determines that a distributed amplification strategy proves optimal for satellite networks, while direct distribution of discrete variable resources is best suited for ground-to-satellite communication, offering valuable insights for the development of practical quantum networks.

Satellite Quantum Communication, Entanglement and Key Distribution

This research comprehensively investigates satellite-based quantum communication, focusing on distributing entanglement and establishing secure keys over long distances. Scientists compare continuous and discrete variable approaches to encoding quantum information, addressing practical challenges like atmospheric turbulence and signal loss. The study demonstrates the feasibility of quantum key distribution using continuous variables, even with atmospheric disturbances and signal attenuation. The research relies on mathematical modeling and computer simulations to analyze quantum communication schemes, using realistic atmospheric models to simulate signal distortion and loss, and quantum information theory to quantify performance.

The team explores techniques like noiseless linear amplification and quantum scissors to boost weak signals and improve performance, while considering limitations imposed by finite quantum signals. Results demonstrate that noiseless linear amplification significantly enhances continuous variable quantum key distribution, enabling longer transmission distances and higher key rates. Entanglement distillation techniques prove crucial for overcoming noise and loss, allowing for the distribution of high-quality entangled states over vast distances. The study highlights the importance of considering finite-size effects in practical quantum key distribution systems. By comparing continuous and discrete variable approaches, the research identifies the strengths and weaknesses of each, revealing that continuous variable quantum key distribution is more robust to certain types of noise.

Entanglement Distribution via Free-Space Optical Links

This research pioneers innovative methods for distributing entanglement, a crucial resource for future quantum networks, by exploring both satellite-based and ground-to-satellite communication strategies. Scientists developed a framework to assess the performance of different entanglement distribution protocols, focusing on discrete-variable and continuous-variable quantum resources. The study examines two configurations: a relay system and a distribution system where the intermediary generates the entangled resource. To model realistic communication channels, the team engineered a detailed analysis of free-space optical links, accounting for signal loss and atmospheric turbulence.

Experiments employed a pure-loss channel model and asymmetric stochastic channels to represent fluctuating ground-to-satellite conditions, characterizing these channels in terms of transmissivity. The team investigated the benefits of distributed noiseless linear amplification, a technique that enhances entanglement without adding noise, and compared its performance to standard amplification strategies. They introduced a novel approach to modeling noiseless linear amplification using first-order quantum scissors. By applying this technique to both relay and distribution configurations, scientists accurately predicted the performance of entanglement distribution schemes under various conditions, establishing a clear pathway for optimizing entanglement distribution in future quantum networks.

Triple-Satellite Entanglement Distribution Achieves High Fidelity

This work details a breakthrough in distributing entanglement, a key requirement for future quantum networks, by exploring methods for linking spatially separated points with high fidelity and rate. Researchers investigated two network configurations, a triple-satellite network and a ground-to-satellite-to-ground network, and two entanglement distribution schemes: relaying an existing entangled resource and generating it at a central node. The study establishes bounds on the rate of distillable entanglement achievable by each protocol, considering discrete-variable and continuous-variable resources, with or without probabilistic noiseless linear amplification. Experiments reveal that for a triple-satellite network, employing a distributed probabilistic noiseless linear amplification scheme yields optimal performance for both continuous-variable and discrete-variable resources.

Conversely, for a ground-to-satellite-to-ground network, distributing a discrete-variable resource via the central satellite proves most effective. Detailed analysis of atmospheric channels demonstrates the superior scaling of the relay configuration. Further investigations into realistic atmospheric channels confirm that the superior scaling of the relay configuration can overcome increased loss associated with uplink channels. Results demonstrate that employing noiseless linear amplification in both discrete-variable and continuous-variable systems significantly enhances entanglement distribution rates, paving the way for long-distance quantum communication.

Optimal Entanglement Distribution in Satellite Networks

This research demonstrates a detailed analysis of entanglement distribution protocols for future quantum networks, specifically examining configurations involving satellites in low-Earth orbit. Scientists investigated two network topologies and two entanglement distribution schemes: relaying an existing entangled resource and generating it at a central node. The study determined that for a triple-satellite network, employing a distributed probabilistic noiseless linear amplification scheme yields optimal performance for both discrete- and continuous-variable resources. Conversely, for ground-to-satellite-to-ground networks, distributing a discrete-variable resource via the central satellite proves most effective.

The findings provide a theoretical foundation for designing practical quantum communication networks capable of long-distance entanglement distribution without relying on traditional fibre-optic infrastructure. By modelling atmospheric channels and considering the impact of turbulence and optical properties, the research offers insights into the feasibility of satellite-based quantum networks over continental scales, establishing clear strategies for maximizing entanglement distribution rates and fidelities in these challenging environments. Future research directions include exploring the impact of more complex atmospheric conditions, investigating hybrid protocols combining different amplification schemes, and developing robust error correction techniques to mitigate the effects of noise and loss.