As devices based on quantum mechanics begin to disrupt the technology landscape, space communications are also transitioning to leverage the security and superior performance of quantum communications.
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Daily communications depend heavily on satellites and space in our increasingly digitized and networked civilization. Within these networks, the internet connects computers all around the world. However, modern communication techniques are susceptible to hacking by supercomputers. Networks created by quantum communication promise a more secure alternative, significantly bolstering security beyond current methods.
Quantum Communication
Quantum devices like quantum computers and sensors can be interconnected over great distances through a quantum network. Currently, information is distributed across digital networks using bits, which can be either 0 or 1.
Quantum bits, or qubits, however, operate differently—they can represent both 0 and 1 simultaneously. This is possible because of phenomena like quantum entanglement and superposition, which are not permitted by "classical physics."
This capability stems from quantum phenomena such as entanglement and superposition, which defy the rules of classical physics. The adoption or enhancement of functionalities in communications, positioning, and timing can significantly benefit from these quantum effects.
This feature of quantum mechanics will enable unprecedented levels of processing power, privacy, and security, among other innovative advancements that are unattainable with current approaches. For instance, operations that would take years to complete on the current fastest computer could be completed in minutes using quantum computers.
Creating a quantum network necessitates connecting numerous points around the globe. The transport of quantum information between distant terminals is the basis of quantum communications. The same characteristics that make quantum communication secure also make network implementation challenging.
Measuring a quantum state destroys the state but preserves the information. Thus, data copies are not retainable. This contrasts with conventional networks, where parts of a data packet can be read and rerouted to a different location within the network.
Many governments have already started to invest in the development of quantum communication technologies to overcome the limitations of existing technologies.
On the ground, secure communication is achievable with the current generation of quantum secure systems. Expanding these systems into airborne and space domains is critical for connecting extensive networks of far-off nodes. While some fundamental quantum-safe solutions have been conceptualized and partially created, further research and development are required for more sophisticated and widely used applications.
By ensuring the safety of information transfer over the long term and guarding against possible assaults, including those anticipated from quantum computers, quantum communications are positioned to set secure communication standards.
Quantum Key Distribution
Quantum Key Distribution (QKD) is a secure communication method that uses quantum physics to construct a cryptographic protocol. The foundation QKD relies on issuing secret keys to secure the information from outside theft attempts.1 QKD has two primary types of protocols: entanglement-based (ENT-QKD) and prepare and measure (PM-QKD).
QKD systems based on PM-QKD, of which BB84 is the most popular, have achieved commercial maturity for ground fiber connections. The BB84 protocol, formulated by Charles Bennett and Gilles Brassard in 1984, exchanges qubits through a quantum channel to produce a shared critical impenetrable to outsiders. PM-QKD has been demonstrated on fiber networks, achieving key exchange rates exceeding one million secure bits per second.
QKD is also being developed for space channels. These linkages, featuring "trusted" nodes that allow for temporary key storage, aim to facilitate key exchange networks on a global scale.
ENT-QKD represents another promising approach, leveraging a photon-pair source situated midway between two terminals for key generation. The foundation of these protocols is quantum entanglement. Being able to communicate any quantum state makes it a more versatile communication method. It can provide security applications outside quantum cryptography and will be the basis for a future quantum internet.
However, entanglement-based protocols, including long fiber connections or high-altitude space-based optical systems, are significantly harder to implement in high-loss scenarios. Therefore, such entanglement-based protocols are still under exploration for future robust implementation.
Quantum repeaters play a crucial role in this ecosystem, positioned at each node within a quantum network. They function akin to memory drives, temporarily storing information before securely relaying it further, thus facilitating secure communications.
Future Outlooks
Numerous research efforts at both academic and industrial levels are dedicated to optimizing QKD. Recent advancements have shown the feasibility of satellite-based entanglement distribution over 1200 kilometers2 and the design of a satellite-based quantum light source for extended physical theory tests in space.3
The development of optical quantum space-to-ground links and a constellation of QKD satellites will facilitate the exchange and distribution of safe encryption keys to billions of devices worldwide. With quantum keys now being created from high-quality random sources and dispersed over cloud networks, increased resilience to potential hacking attacks can be resized.
In addition to fundamental research, space quantum technologies are anticipated to open the door to other pertinent quantum communications applications outside quantum cryptography, including temporal distribution, metrology, and distributed quantum computation.
To accelerate the progress of space quantum communication, interdisciplinary research and development are essential, alongside concrete operational improvements. These include the creation of inter-satellite links, low-loss space-to-ground communications employing adaptive optical systems, high-rate QKD payloads, and sophisticated pointing systems.
Various new applications involving time, position, and navigation will require further exploration for QKD protocols using various photonic degrees of freedom. This will necessitate advanced security analyses and the establishment of frameworks to facilitate new, practical, and cost-effective services while ensuring the highest level of security.
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References and Further Reading
- Quantum Technologies in Space. (2019). Quantum Technologies in Space- Policy White Paper. [Online]. Quantum Technologies in Space. Available at: https://qtspace.eu/wp-content/uploads/2023/08/QT-In-Space-White-Paper-Final_0.pdf
- Yin, J., et al. (2017). Satellite-based entanglement distribution over 1200 kilometers. Science. DOI:10.1126/science.aan3211
- Ahmadi, N., et al. (2024). QUICK3 - Design of a Satellite-Based Quantum Light Source for Quantum Communication and Extended Physical Theory Tests in Space. Adv Quantum Technol. doi.org/10.1002/qute.202300343
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