ADELPHI, Md. -- Army scientists have proposed a promising architecture for creating quantum secure networks using realistic quantum memories that will provide future Soldiers tactical advantages on the battlefield.

Quantum secure networks use entanglement between the network nodes for secure communications.

The security of the data-in-transit is guaranteed by the laws of quantum mechanics and is secure against eavesdropping even when the adversary has quantum computational resources.

Moreover, such networks can be used for quantum-limited, rather than classically-limited, sensing and navigation, researchers said.

Dr. Vladimir S. Malinovsky, physicist, and Dr. Siddhartha Santra, a postdoctoral fellow at the U.S. Army Combat Capabilities Development Command's Army Research Laboratory, along with collaborators at Yale University, are the first to propose a quantum repeater architecture using realistic quantum memories that maximizes the entanglement generation rate between distant nodes of a quantum network.

The proposal mitigates the loss of entanglement quality affecting the operation of currently available quantum memories that may be used in near-term quantum networks.

This work is detailed in the publication titled "Quantum repeater architecture with hierarchically optimized memory buffer times" in the March issue of the journal Quantum Science and Technology (See Related Links below).

Further, the CCDC ARL researchers, along with collaborators at the University of Maryland, College Park, have proposed a scheme based on trapped-ions that can potentially implement such optimized repeater protocols.

These findings are described in the group's publication, "Quantum repeaters based on two species trapped ions," in the July issue of New Journal of Physics.

"Quantum networks, once realized, hold great promise for the future Soldier," Malinovsky said. "The entanglement in quantum states shared between multiple parties is a valuable resource that can be used for unhackable secret sharing, authentication and identification. This provides the highest level of communication security. The key to realizing these potential applications is maximizing the entanglement generation rate in these networks overcoming the limitations of near-term quantum devices such as imperfect quantum memories."

Their proposal utilizes the physical idea of optimizing the quantum memory-buffer time in a nested manner for all levels of a quantum repeater network so that the rate of entanglement generation can be increased for arbitrary distances between the nodes, Santra added.

According to Malinovsky, given that quantum memories in a variety of quantum hardware platforms are coming online, protocols for utilizing these memories optimally for entanglement generation are timely.

"In the near-term the quality of these quantum memories will not be perfect," Malinovsky said. "Devising methods to maximize entanglement generation so that some of the promised applications become feasible despite limited memory quality and quantity is a crucial stepping stone towards large-scale quantum networks."

According to Santra, the protocols they have proposed are significant because they can be readily used to address the crucial problem of loss of entanglement quality in quantum memories used in networks without requiring much experimental overhead.

"The entanglement distribution rate is the limiting factor to achieve enhanced performance and increased capability in quantum network applications like communication, sensing and computing," Santra said. "Our results allow us to extract rates that are many orders of magnitude higher that achievable previously."

This research supports the Command, Control, Communications, Intelligence Cross-Functional Team, as it involves creating new avenues for communication and computing.

"The research topic and approach were developed through our group's intensive interactions with our collaborators," Malinovsky said. "The solution required joint expertise from multiple disciplines. Importantly, our approach facilitates the use of near-term quantum hardware for high-rate entanglement generation."

Malinovsky said the research has been well received in the quantum information research community as well as of great potential for the Army of the future.
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The CCDC Army Research Laboratory (ARL) is an element of the U.S. Army Combat Capabilities Development Command. As the Army's corporate research laboratory, ARL discovers, innovates and transitions science and technology to ensure dominant strategic land power. Through collaboration across the command's core technical competencies, CCDC leads in the discovery, development and delivery of the technology-based capabilities required to make Soldiers more lethal to win our Nation's wars and come home safely. CCDC is a major subordinate command of the U.S. Army Futures Command.