The ORNL study used light particles, or photons, as qubits and transmitted the polarization-entangled qubits on photon pairs via quantum entanglement distribution. Entangled qubits are so intertwined that one can’t be described independently of the other. That entanglement allows the information encoded in qubits to be transmitted from one place to another via quantum teleportation without physical travel through space. Entanglement distribution and quantum teleportation form the bedrock of more advanced quantum networks.
Photons can be encoded as qubits via polarization, along with other properties of light, and can be transmitted over existing fiber-optic cable systems. But wind, moisture, changes in temperature and other stresses on the cable can disrupt the photons’ polarization and interfere with the signal. Chapman and the ORNL team wanted to find a way to stabilize the polarization and reduce interference while keeping the network running at maximum bandwidth.
“Most previous solutions didn’t necessarily work for all types of polarizations and required trade-offs like periodically resetting the network,” Chapman said. “People using the network need it up and running. Our approach controls for any type of polarization and doesn’t require the network to periodically shut down.”
Chapman and Alshowkan tested the compensation method by generating test signals from entangled photons using entanglement-assisted quantum process tomography, which estimates the properties of a quantum channel — such as the in-ground fiber with APC — to measure for changes. The transmissions remained relatively stable with minimal added noise when APC was enabled.
“An experienced musician with a good ear can tell the difference when two instruments are out of tune,” Chapman said. “In our APC, we’re using a laser to do the same thing with our reference signals.”
Chapman has applied for a patent on the method. Next steps include adjusting the approach to increase bandwidth and compensation range to enable high-performance operation under a wider variety of conditions.
“Working with organizations like ORNL provides valuable feedback for how we can continue to enhance EPB Quantum Network as a resource for researchers, startups and academic customers,” said David Wade, EPB’s CEO. “Since launching a commercially viable quantum network, we’ve begun working to prepare our community to benefit from the advancements in the quantum future and establish Chattanooga as a destination for developers and investment.”
UTC officials pledged to continue their support.
“We’re excited about being part of this successful teamwork,” said Reinhold Mann, vice chancellor for research at UTC. “This partnership advances quantum information science and technology and adds to our special experiential learning offering for our students."
Support for this research came from the ORNL Laboratory Directed Research and Development program, from the DOE Office of Science’s Advanced Scientific Computing Research program and from the UTC Quantum Initiative.
In celebration of the International Year of Quantum Science and Technology in 2025, ORNL continues to empower the pursuit of quantum innovation, advancing world-leading scientific discovery to enable a quantum revolution that promises to transform a vast range of technologies critical to American competitiveness. Learn more about Quantum Science at ORNL.