Quantum Loop Provides Testbed for Unhackable Communications

Scientists from the U.S. Department of Energy’s (DOE) Argonne National Laboratory and the University of Chicago (UChicago) have launched a quantum loop, consisting of two connected, 26-mile fiber optic cables that run between Argonne and the Illinois tollway near Bolingbrook, Ill., and back. At 52 miles, it is one of the longest ground-based quantum communication channels in the country, the team said.

The loop will serve as a testbed for researching the use of quantum physics to send unhackable information across long distances and will help scientists identify and address the challenges of operating a quantum network. Researchers at Argonne and UChicago will also use the testbed to explore quantum entanglement.

Scientists Joe Heremans, Alan Dibos, and Gary Wolfowicz demonstrated the operation of the testbed by generating and transmitting optical pulses through one and then both fiber loops. They witnessed a delay of 200 microseconds for the transit time of the laser pulse along one fiber loop, which is consistent with the speed of light in the glass optical fiber.

They are using the loop for a series of experiments, including transmitting signals from photons emitted from ensembles of ions, which could be used as a quantum memory for the network. A functional quantum memory, which entails the storage and retrieval of quantum states, is a key advance needed for quantum communication and a quantum internet.

Argonne scientists, (l) to (r) Sean Sullivan, Gary Wolfowicz, Joseph Heremans, and Alan Dibos, worked on the quantum loop project and demonstrated the operation of the testbed by generating, transmitting, and detecting optical pulses through one and then both fiber loops. Courtesy of Argonne National Laboratory.

“We will need many of these quantum memories spaced out over about 100 kilometers to relay the quantum signal through a network,” Tian Zhong, Argonne scientist and University of Chicago assistant professor, said. “The quantum loop enables us to test and refine this quantum memory technology before deploying it in large scale.”

Principal investigator David Awschalom said that the loop could be scaled to test and demonstrate communication across even greater distances, to help lay the foundation for a quantum internet.

In addition to the quantum loop, Argonne plans to develop a two-way quantum link network with Fermi National Accelerator Laboratory. When the two projects are connected, the quantum link is expected to be among the longest links in the world for sending secure information using quantum principles.