Satellite-Based Entanglement Distribution Over 1200 kilometers

Abstract: Long-distance entanglement distribution is essential both for foundational tests of quantum physics and scalable quantum networks. Owing to channel loss, however, the previously achieved distance was limited to ~100 km. Here, we demonstrate satellite-based distribution of entangled photon pairs to two locations separated by 1203 km on the Earth, through satellite-to-ground two-downlink with a sum of length varies from 1600 km to 2400 km. We observe a survival of two-photon entanglement and a violation of Bell inequality by 2.37+/-0.09 under strict Einstein locality conditions. The obtained effective link efficiency at 1200 km in this work is over 12 orders of magnitude higher than the direct bidirectional transmission of the two photons through the best commercial telecommunication fibers with a loss of 0.16 dB/km.

• The paper demonstrates satellite-based entanglement distribution over 1203 km, verifying quantum non-locality by violating Bell inequality.
• The effective link efficiency achieved at 1200 km is more than 12 orders of magnitude higher compared to transmission using the best commercial fiber optic cables.
• This work lays the groundwork for global quantum networks and provides a new platform for testing fundamental quantum mechanics over vast distances.

Satellite-Based Entanglement Distribution Over 1200 Kilometers

The paper "Satellite-Based Entanglement Distribution Over 1200 kilometers" presents a substantial advancement in the field of quantum communication by demonstrating a long-distance entanglement distribution via satellite. The research addresses the fundamental and practical challenges associated with the distribution of entangled particles, which is essential for both the study of quantum mechanics under extreme conditions and the potential deployment of scalable quantum networks.

Summary of Findings

The study successfully demonstrates the satellite-based distribution of entangled photon pairs between two ground locations on Earth, separated by 1203 kilometers. This feat was achieved by employing satellite-to-ground two-downlink channels with a total length that varied between 1600 km and 2400 km. The following key results were obtained:

• Violation of Bell Inequality: The observed survival of two-photon entanglement and the violation of Bell inequality by 2.37±0.09 under strict Einstein locality conditions underscore the non-local nature of quantum entanglement.
• Higher Link Efficiency: The effective link efficiency at 1200 km was more than 12 orders of magnitude higher than what could be achieved through direct bidirectional transmission using the best commercial telecommunication fibers, even with an optimal loss rate of 0.16 dB/km.

Experimental Approach

The experiment utilized a satellite-based platform named Micius to overcome the significant challenges posed by photon loss during transmission over long distances. Key elements of the research include:

1. Spaceborne Entangled Photon Source: The researchers developed ultrabright, robust entangled photon sources to ensure reliable entanglement under the variable conditions experienced during satellite transmission.
2. Acquiring, Pointing, and Tracking (APT) Technology: High-precision APT technology was employed to optimize the efficiency of the satellite-to-ground link. This was crucial for maintaining the integrity of the entangled states over the considerable distances involved.
3. Temporal and Polarization Synchronization: An elaborate synchronization mechanism was implemented using a pulsed laser sent from the satellite, and a motorized waveplate combination was used for on-the-fly polarization compensation.

Theoretical and Practical Implications

These findings have profound implications for the future of quantum communication and fundamental quantum optics:

• Quantum Networks: The successful distribution of entangled particles over such a distance lays the groundwork for the future development of global-scale quantum networks. These networks can significantly enhance the capabilities of existing quantum communication protocols such as quantum teleportation and quantum key distribution.
• Testing Quantum Mechanics: The ability to conduct precise tests of quantum mechanical principles, like the violation of Bell inequality, at such large distances provides a novel platform for probing the foundational aspects of quantum theory under uncharted conditions.

Future Developments and Challenges

The current research marks a significant milestone, yet several challenges remain in the deployment of practical quantum communication systems:

• Integration of Quantum Repeaters: Despite significant progress in the development of quantum repeater technology, integrating all necessary functionalities (e.g., long storage times and efficient retrieval) remains a complex endeavor.
• Technological Advancements: Further advancements in satellite technology, including better photon detection and reduced channel loss, will be necessary to expand the reach and reliability of such systems.

In conclusion, this work demonstrates the feasibility of satellite-based entanglement distribution, opening new avenues for both practical applications in quantum communication and further explorations of quantum mechanics. The method detailed in this research is poised to play a pivotal role in the realization of a global quantum communication infrastructure.