Researchers realize quantum communication milestone using light

Few terms are more common in the scientific arena these days than ‘quantum’.

Technologies based on the notoriously cumbersome laws of quantum mechanics promise to make computers much more powerful than today’s fastest supercomputers, unparalleled secure communications and unprecedented perceptiveness required for further scientific discovery.

But to bring these technologies to light, researchers need to develop efficient quantum communication networks that connect quantum devices while maintaining the delicate conditions of the particles used to transmit information.

A team of researchers from the Department of Energy’s Oak Ridge National Laboratory, along with colleagues at Purdue University, have taken an important step toward this goal by harnessing the frequency or color of light. Such capabilities can contribute to more practical and large-scale quantum networks that are exponentially more powerful and secure than the classic networks we currently have.

Specifically, the team utilizes the properties of light and the principles of quantum mechanics to transmit information, making the network itself a photonic quantum information processor. This approach is promising for several reasons.

To begin with, photons move at the speed of light so that the information can move as fast as possible from point A to point B. Photons usually do not alternate with each other or with the surrounding environment, ensuring that the information is not confused or damaged along the way. “Light is actually the only viable option for long-distance quantum communication,” said project leader Joseph Lukens, an ORNL researcher, Wigner Fellow and DOE Early Career Award winner, who helped shape the team’s results. Physical overview letters.

The team used light to produce frequency bakewigs, or single photons that reside simultaneously in two different frequencies, to demonstrate, for the first time, fully arbitrary communication operations in frequency coding. Although frequency coding and entanglement occur in many systems and are naturally compatible with optical fiber, it is traditionally difficult to use these phenomena to manipulate and process data. However, such operations are necessary for basic network functions in quantum communication and, by extension, the realization of a wide range of quantum technologies.

Using a technology developed at ORNL, known as a quantum frequency processor, the researchers demonstrated quantum gates that are widely applicable, or the logical operations required to execute quantum communication protocols. In these protocols, researchers must be able to manipulate photons in a user-defined way, often in response to measurements performed on particles elsewhere in the network. While the traditional operations used in classical computers and communication technologies, such as AND and OR, operate on digital zeros and one individually, quantum gates operate on simultaneous superpositions of zeros and one, protecting the quantum information as it passes through, a phenomenon required real quantum network.

By proving that their configuration could transform any qubit state into another qubit state, the team demonstrated practical information transfer. “If you can do arbitrary operations, you can do any of the fundamental quantum communication protocols such as frequency conversion routing,” Lukens said.

This is one of the many different systems, but one of the most promising considering the results. As an example, the team successfully demonstrated more than 98% fidelity – a quantitative measure of accuracy – using their custom setup.

Although the frequency network of quantum networks has historically been difficult to control, the team’s toolbox makes it much more controllable. Not only that, it’s a naturally manufactured system that can translate well to existing fiber optics. In fact, the system is designed by classical telecommunication components such as phase modulators. These factors make the technology cheaper and more attractive to industries that want to apply it. Furthermore, this domino effect promotes both classical and quantum communication simultaneously, thus advancing the team’s methods and possibly bringing large – scale quantum networks one step closer to reality.

Their next experiment is about implementing their system on a photonic integrated circuit. “There are a lot of unforeseen applications,” Lukens said. “Frequency coding is, of course, manufactured by many different systems, and it is very well suited for optical fiber, so the potential application space must be spacious.”