Satellite-relayed intercontinental quantum network (1801.04418v1)

Abstract: We perform decoy-state quantum key distribution between a low-Earth-orbit satellite and multiple ground stations located in Xinglong, Nanshan, and Graz, which establish satellite-to-ground secure keys with ~kHz rate per passage of the satellite Micius over a ground station. The satellite thus establishes a secure key between itself and, say, Xinglong, and another key between itself and, say, Graz. Then, upon request from the ground command, Micius acts as a trusted relay. It performs bitwise exclusive OR operations between the two keys and relays the result to one of the ground stations. That way, a secret key is created between China and Europe at locations separated by 7600 km on Earth. These keys are then used for intercontinental quantum-secured communication. This was on the one hand the transmission of images in a one-time pad configuration from China to Austria as well as from Austria to China. Also, a videoconference was performed between the Austrian Academy of Sciences and the Chinese Academy of Sciences, which also included a 280 km optical ground connection between Xinglong and Beijing. Our work points towards an efficient solution for an ultralong-distance global quantum network, laying the groundwork for a future quantum internet.

• The paper demonstrates intercontinental quantum key distribution via the Micius satellite, securely bridging a 7600 km gap between China and Europe.
• It employs a decoy-state BB84 protocol with weak coherent laser pulses to achieve key rates up to 9 kb/s with quantum bit error rates as low as 1.0%.
• The network successfully supports real-time secure communications, such as image transfers and video conferencing, paving the way for a global quantum internet.

Satellite-Relayed Intercontinental Quantum Network

The paper presents the demonstration of intercontinental quantum key distribution (QKD) achieved via a low-Earth-orbit satellite known as Micius. The research showcases a novel approach to secure quantum communication across vast distances, specifically enabling secure communication between China and Europe—a separation of approximately 7600 km. This work addresses the crucial challenge of extending QKD over ultra-long distances to pave the way towards establishing a global quantum network.

Key Methodologies

The researchers utilized the satellite Micius, equipped for QKD using a space-qualified transmitter, to distribute secure quantum keys to ground stations in Xinglong, China; Nanshan, China; and Graz, Austria. The satellite employs a decoy-state BB84 protocol, leveraging weak coherent laser pulses with a wavelength of ~850 nm. Micius acts as a trusted relay between the ground stations, facilitating secure key exchanges by performing bitwise XOR operations on shared keys. The optical ground link incorporates robust techniques, such as narrow beam divergence and high-accuracy tracking, to minimize channel loss due to atmospheric effects.

Results and Performance Metrics

The experiments yielded significant results with QKD operations in a downlink scenario. Secure keys were generated with rates of approximately 3 kb/s at a 1000 km distance and 9 kb/s at a 600 km distance. The observed quantum bit error rates (QBER) ranged between 1.0% and 2.4%, indicating efficient error mitigation mechanisms against background noise and polarization errors. The experimental setup routinely achieved sifted key rates and established final keys in the range of several hundred kilobits.

Demonstrations and Practical Applications

The practical application of this quantum communication network was demonstrated through secure intercontinental communication endeavors. Pictures were successfully transferred between Beijing and Vienna using one-time-pad encryption, underscoring the irreversible nature of the secure key exchange. Additionally, a video conference between academic institutions in China and Austria utilized a 280 km optical fiber link to connect the Xinglong ground station with a metropolitan network in Beijing, highlighting the integration flexibility of the satellite-relayed quantum network with existing infrastructures.

Implications and Future Directions

The work discussed in this paper sets the foundational stage for a future quantum internet by demonstrating satellite-based QKD as an efficient solution for long-distance secure communication. While the current setup relies on a trusted relay model, upcoming iterations could explore entanglement-based approaches for enhanced security. Furthermore, expanding coverage and operational times through higher-orbit satellites, multitasking between satellite and ground station networks, and potential extensions to broader geographical areas will likely be the focus of future explorations. Such advancements may well-amplify the applicability and robustness of quantum communication systems on a global scale.