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Brian Kirby (right) and Michael Brodsky of the U.S. Army Research Laboratory experiments on how physical properties of fibers affect the distributed entanglement necessary for quantum networking. The ARL project, led by Daniel Jones, who is not pictured, is part of the Defense Laboratory Quantum Science and Engineering Program. Army photo by Jhi Scott

Brian Kirby (right) and Michael Brodsky of the U.S. Army Research Laboratory experiments on how physical properties of fibers affect the distributed entanglement necessary for quantum networking. The ARL project, led by Daniel Jones, who is not pictured, is part of the Defense Laboratory Quantum Science and Engineering Program. (Courtesy of the U.S. Army/Jhi Scott)

Department of Defense Laboratories are on a quest to assemble the first fiber optics test bed and small-scale network aimed at quantum network experiments.

Quantum networks promise unsurpassable capabilities in network and communication security, such as new secret-sharing and encryption protocols, authentication and digital signatures solutions, as well as efficient and secure distributed computations.

The U.S. Army Research Laboratory reached a milestone through its development of theoretical and experimental understanding of the effects a certain common physical property of telecom fibers and components, called polarization dependent loss on the quality and transmission rate of entangled photons.

The novelty of this study is the situation in which polarization of photons is subject to random transformation and reorientation due to changing ambient conditions, a scenario pertinent to a realistic fiber optics environment. This required a new mathematical approach.

“We consider how polarization dependent loss affects the quality and transmission rate of entangled photon pairs, when two photons of each pair traverse two different fibers leading from a central node to opposite edges of a network,” said Michael Brodsky, quantum physicist at ARL.

The scientists devised a concise analytical model describing the effect, verifying it in the lab-based entanglement distribution testbed and invented a compensation method in which polarization dependent loss in one fiber could counteract the destructive effect of the other fiber’s polarization dependent loss.

Brodsky said quantum networks would allow for the transmission of quantum information between physically separated quantum processors. Quantum networking deals with creation and manipulation, routing and distributing of quantum logical states between distant network nodes. These quantum states could consist of two or more quantum bits, or qubits, that are connected to each other in a very peculiar way. This special connection, which in physics parlor is called quantum entanglement, serves as the basis for quantum communications.

Army scientists would like to one day provide the use of quantum networks to achieve ultra-secure communications that are tamper-evident and can provide more efficient processing of information for data-to-decisive actions, said Dr. Thomas Russell, Deputy Assistant Secretary of the Army for Research and Technology in a statement in March before the Subcommittee on Emerging Threats and Capabilities, Committee on Armed Services, U.S. House of Representatives.

One of the preliminary tasks of designing fiber test beds for quantum network experiments calls for fundamental understanding of how physical properties of fibers and other components affect distributed entanglement quality and transmission rates.

Army scientists will continue work as part of the DOD QSEP Program to expand the body of knowledge required to realize quantum networking.

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