By U.S. Army CCDC Army Research Laboratory Public AffairsJanuary 9, 2020
ADELPHI, Md. -- Army scientists have developed a radically new quantum device that can store many quantum excitation patterns at once, opening the door for the creation of a quantum network.
A quantum network is the Holy Grail for scientists because it likely can never be wiretapped and it would offer extraordinarily powerful computing and sensing capabilities.
Researchers from the Quantum Science Group at the U.S. Army Combat Capabilities Development Command's Army Research Laboratory constructed a test-bed quantum networking apparatus, consisting of millions of rubidium atoms trapped within laser beams and cooled to nearly absolute zero.
"Most leading quantum information platforms are working toward increased capacity bit-by-bit," said Dr. Kevin Cox. "This includes, for example, quantum computers based on trapped atomic ions that increase their computing power by trapping ions one-by-one. Our platform is distinct because we use a large ensemble of atoms, over a million, and instead store quantum excitations as patterns or images."
There is a worldwide race between research groups to develop quantum devices that can perform ultra-secure networking and computation. The lab's new results are a big step toward achieving these goals, researchers said.
To imagine this technology better, picture a canvas or sea in which quantum images or waves can be written, Cox said. Those images or wave patterns, called spin-waves, can then be stored as information. Spin-waves are like the paint for Cox's metaphorical canvas.
"Nobody in the world has yet been able to demonstrate a quantum repeater, a device that can teleport quantum information over a long distance network," said Dr. Paul Kunz, a physicist in the quantum science group. "Our new results show a significant step forward towards realizing such a device."
A quantum repeater connects quantum devices. It's the first step toward a fully-fledged quantum internet, researchers said.
"The apparatus's circuits are light and laser beams instead of wire," Kunz said.
The quantum science group has shown their system already has the potential to store hundreds if not thousands of quantum bits, making it a promising candidate for scaling up quantum information systems.
Laser beams reflect off of four mirrors, creating an optical cavity, like a one-directional racetrack for light. The racetrack passes directly through the glass chamber so that light interacts with the rubidium atoms on every pass.
"The optical cavity dictates that all of the quantum information is directed along one path and can easily be routed into an optical fiber or other communication channel," Cox said.
Together with the multiplexing capacity, the one-directional light racetrack design forms a pivotal and unique quantum system.
Other research groups have investigated high-capacity quantum interfaces; however, the quantum information was not controlled in a single, targeted direction. Instead, it was emitted in random directions, making it hard to use, or integrate into a quantum network.
Scientists said quantum entanglement is the crucial resource that will enable extraordinary quantum technologies in the future. Quantum entanglement is the phenomenon where measuring one quantum object has an instantaneous effect on another quantum object.
"It is a quantum connection between two objects, and has no equivalent in the normal world," Cox said.
The main focus for scientists from ARL's quantum science group research is how to create, control and use quantum entanglement.
"Capabilities that rely on quantum entanglement, such as quantum secure communication, entanglement-enhanced quantum sensors or quantum networks, cannot be mimicked by traditional technologies," Cox said.
Unhackable quantum networks could be a game-changer in cryptography.
The possible technological advancements through quantum entanglement seem enormous, Cox said. But it's important to keep in mind that this is a critical first step in launching quantum science into the next 10 to 20 years.
"Entanglement-based technologies offer huge potential combat advantages for our future Soldiers," he said. "Among those are remote access to ultra-powerful quantum computers, un-tappable secure networks and communication, and exquisite and assured sensors for timing and navigation as well as detection of adversaries."
The Army is working on new applications and technologies that take advantage of atomic quantum properties
"Vapors of atoms already form the most precise clocks, magnetic field sensors, electric field sensors, rotation, acceleration and gravitational sensors," Kunz said. "Yet, we know it is possible to improve these even further through leveraging entanglement."
The Army first conducted research on a multiplexed quantum interface in 2018. Army researchers contributed to "Spin-Wave Multiplexed Atom-Cavity Electrodynamics," published Dec. 24 in Physical Review Letters. Contributing authors include: Kevin C. Cox, David H. Meyer, Zachary A. Castillo, Fredrik K. Fatemi, and Paul D. Kunz.
The scientists from the quantum science group have their eyes fixed on the future of quantum technologies.
"The work reported in this paper is really exciting because this experimental apparatus is the only one of its kind in the world," Kunz said. "It brings two critical ingredients together into a single system: strong light-matter coupling and high-capacity multiplexing. Bringing these ingredients to bear on quantum entanglement creation and distribution opens so many possibilities for advancing quantum technologies."
CCDC Army Research Laboratory is an element of the U.S. Army Combat Capabilities Development Command. As the Army's corporate research laboratory, the lab 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.