By U.S. Army CCDC Army Research Laboratory Public AffairsJanuary 27, 2020
ADELPHI, Md. -- Army scientists and University of Maryland partners recently published a study showing how they combined two different quantum technologies to produce a timing synchronization tool for future quantum networks.
One day soon, researchers hope to use quantum computer networks to handle and process information in a vastly different way than current, or classical computers. Quantum computers will perform more complicated computations, according to leading scientists.
For future Soldiers, a quantum computer network would potentially create ultra-secure communications and bring about advanced artificial intelligence agents.
As with classical computer networks, Army researchers said a viable quantum network will likely require more than one kind of component. A hybrid system may be the key to quantum networking.
A team from the U.S. Army Combat Capabilities Development Command's Army Research Laboratory partnered with University of Maryland researchers to demonstrate the first instance of photons emitted by a trapped ion interacting with neutral atoms.
Army physicist Dr. Qudsia Sara Quraishi from the lab's Sensors and Electron Devices Directorate, along with University of Maryland postdoctoral researcher Dr. James Siverns and graduate student John Hannegan, demonstrated that trapped ion-produced photons and neutral atoms are compatible as quantum systems through the use of slow light.
Light travels at about 186,000 miles per second; however, researchers have been able to slow light to one mile per hour using an exotic material known as Bose-Einstein Condensate. In 2001, physicists actually managed to stop light in a vapor of rubidium gas. Scientists said this is important for quantum networks.
"Slow light was first demonstrated 20 years ago at Harvard, but significant development was needed to integrate it with photons from trapped ions and this is the first result that combines photons from a trapped ion with neutral atoms," Quraishi said. "Each of these systems on their own have generated significant results in quantum information, so that ability to demonstrate a useful networking tool by combining them together is exciting."
Quantum networks transmit information in what's known as quantum bits, also called qubits, between physically separated quantum processors, according to Scientific American.
Photons serve as ideal carriers of information in a quantum network due to their high speed and, at certain wavelengths, low absorption losses when traveling long distances via optical fiber or in free space.
On the other hand, neutral atoms can make up versatile quantum systems that can hold onto quantum information for a relatively long period but are stationary and, therefore, poor at transmitting data over distances.
By connecting two quantum systems, Army and University of Maryland researchers ultimately opened the door to brand-new tools in the field of quantum communication, useful for timing synchronization between quantum systems.
This effort involved interactive work on quantum frequency conversion, which is part of an Army Small Business Innovation Research managed by Quraishi.
Slowing photons requires carefully setting their frequency to be half-way between two transitions in the neutral atomic system; however, photons produced by trapped ions are at a completely different frequency than the neutral atom system.
Quraishi's group overcame this challenge by using a customized quantum frequency converter, which built upon the group's previous work to change the frequency of the ion-produced photons to match that of the neutral atomic system.
The researchers trapped a single barium ion in a customized vacuum system designed for optimal collection of single photons generated by the ion. They converted the frequency of the photon and sent it to an atomic delay line consisting of a glass cell containing a vapor of neutral atoms, i.e., rubidium vapor.
Quraishi's team subsequently employed this slow light in the rubidium vapor to delay the trapped ion by up to 13.5 nanoseconds via a user-controlled tunable delay. This delay is a significant fraction of the photon's length and sufficient to synchronize two quantum sources.
Researchers can modify the length of the delay without disrupting the quantum properties in the systems, which is important, Quraishi said.
"By tuning the temperature of the cell, we were able to control the number of atoms in the vapor, where increasing the atom number slows the photons down," Quraishi said. "The slowing happens because the interaction of the photons with the atoms changes their group velocity."
Realistically, scalable quantum systems need to manage these components in order to remain practical, she said. Since each type of quantum system comes with its own strengths and weaknesses, combining different platforms will allow scientists to assemble distinct quantum networks that consist of only the best components of each system.
Advancements in quantum communication and computation serve a vital role in ensuring mission success for the future warfighter, she said. By creating quantum networking tools, research in this field keeps the Army ahead of, and participating in, the latest developments in quantum networking technologies.
"Securing communications is vital for Army operations and this work seeds efforts in quantum networking by demonstrating a needed element in networking, tunable communication delay for synchronization," Quraishi said. "Prior to this work, delays would largely rely on optical fiber, which is not suitable for all Army operations. Connecting different quantum technologies together will extend the range of application, offer enhanced performance, and bring disparate Army systems together."
In the spirit of the lab's Open Campus initiative, Quraishi intends to continue her collaboration with the University of Maryland to further explore techniques to integrate various aspects of quantum systems together.
"We hope to form a hybrid quantum network leveraging the differing strengths of each system involved," Quraishi said. "Such a hybrid network could be superior to one that employs only one type of quantum system."
The CCDC Army Research Laboratory 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.