Project shows path to commercial quantum Internet

Researchers at the Oak Ridge National Laboratory (ORNL) in the US have shown the first transmission of an entangled quantum signal using multiple wavelength channels and automatic polarization stabilization over a commercial quantum network with no downtime.

This opens up a practical quantum Internet.

The team worked with telecoms operator EPB of Chattanooga and the University of Tennessee at Chattanooga to use automatic polarization compensation, or APC, to stabilize the polarization, or direction of the electric field oscillation in a light wave, of a signal sent over the EPB’s fibre-optic commercial quantum network. This uses equipment from Qubitekk, now part of IonQ, which is expanding into quantum Internet applications.

The APC uses reference signals generated by lasers to continuously check the transmitted polarization, detected with an ultrasensitive method known as heterodyne detection. This reduces data interference caused by outside forces like wind and temperature changes that can affect the fibre optic cables used to transmit quantum signals.

“One of our goals all along has been to develop quantum communications systems that operate seamlessly for users,” said Joseph Chapman, an ORNL quantum research scientist who led the study and is applying for a patent on the technology.

“This is the first demonstration of this method, which enabled relatively fast stabilization while preserving the quantum signals, all with 100% uptime – meaning the people at either end of this transmission won’t notice any interruption in the signal and don’t need to coordinate scheduled downtime,” he said.

The method enabled continuous transmission of the signals with no interruptions for more than 30 hours between the node on the University of Tennessee Chattanooga campus and two other EPB quantum network nodes, each about half a mile away. The UTC node held an entangled-photon source developed by Muneer Alshowkan, an ORNL quantum research scientist.

Photons can be encoded as qubits via polarization, along with other properties of light, and can be transmitted over existing fibre-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.

“Most previous solutions didn’t necessarily work for all types of polarizations and required trade-offs like periodically resetting the network,” said Chapman. “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.”

The compensation method was tested 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 fibre with APC – to measure for changes. The transmissions remained relatively stable with minimal added noise when APC was enabled.

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.”

EPB operates the world’s fastest community-wide internet service with speeds up to 25 Gbit/s and also uses Chattanooga’s fibre optic network as the communications backbone for a highly automated power distribution system.

The EPB Quantum Network currently has capacity for ten quantum interconnected user nodes across downtown Chattanooga using commercial network equipment designed and manufactured by Qubitekk, including its own APC. The assets of the company were acquired by IonQ two weeks ago.

“APCs are essential components for interconnecting quantum technologies that have the potential to optimize the management of our electrical grids, accelerate the development of new medicines and materials, and strengthen national security with unbreakable encryption,” said Duncan Earl, co-founder and CTO at Qubitekk.

“Collaborative runs like this on real-world networks are critical to developing the array of commercially viable quantum technologies necessary for the U.S. to compete in this rapidly emerging global industry.”